![Linus Torvalds](/assets/img/avatar_default.png)
Yes, the add and remove cases do share the same basic loop and the locking, but the compiler can inline and then CSE some of the end result anyway. And splitting it up makes the code way easier to follow, and makes it clearer exactly what the semantics are. In particular, we must make sure that the FASYNC flag in file->f_flags exactly matches the state of "is this file on any fasync list", since not only is that flag visible to user space (F_GETFL), but we also use that flag to check whether we need to remove any fasync entries on file close. We got that wrong for the case of a mixed use of file locking (which tries to remove any fasync entries for file leases) and fasync. Splitting the function up also makes it possible to do some future optimizations without making the function even messier. In particular, since the FASYNC flag has to match the state of "is this on a list", we can do the following future optimizations: - on remove, we don't even need to get the locks and traverse the list if FASYNC isn't set, since we can know a priori that there is no point (this is effectively the same optimization that we already do in __fput() wrt removing fasync on file close) - on add, we can use the FASYNC flag to decide whether we are changing an existing entry or need to allocate a new one. but this is just the cleanup + fix for the FASYNC flag. Acked-by: Al Viro <viro@ZenIV.linux.org.uk> Tested-by: Tavis Ormandy <taviso@google.com> Cc: Jeff Dike <jdike@addtoit.com> Cc: Matt Mackall <mpm@selenic.com> Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
750 lines
16 KiB
C
750 lines
16 KiB
C
/*
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* linux/fs/fcntl.c
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*
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* Copyright (C) 1991, 1992 Linus Torvalds
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*/
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#include <linux/syscalls.h>
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#include <linux/init.h>
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#include <linux/mm.h>
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#include <linux/fs.h>
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#include <linux/file.h>
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#include <linux/fdtable.h>
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#include <linux/capability.h>
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#include <linux/dnotify.h>
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#include <linux/slab.h>
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#include <linux/module.h>
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#include <linux/security.h>
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#include <linux/ptrace.h>
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#include <linux/signal.h>
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#include <linux/rcupdate.h>
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#include <linux/pid_namespace.h>
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#include <asm/poll.h>
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#include <asm/siginfo.h>
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#include <asm/uaccess.h>
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void set_close_on_exec(unsigned int fd, int flag)
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{
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struct files_struct *files = current->files;
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struct fdtable *fdt;
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spin_lock(&files->file_lock);
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fdt = files_fdtable(files);
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if (flag)
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FD_SET(fd, fdt->close_on_exec);
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else
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FD_CLR(fd, fdt->close_on_exec);
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spin_unlock(&files->file_lock);
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}
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static int get_close_on_exec(unsigned int fd)
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{
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struct files_struct *files = current->files;
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struct fdtable *fdt;
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int res;
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rcu_read_lock();
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fdt = files_fdtable(files);
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res = FD_ISSET(fd, fdt->close_on_exec);
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rcu_read_unlock();
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return res;
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}
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SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)
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{
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int err = -EBADF;
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struct file * file, *tofree;
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struct files_struct * files = current->files;
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struct fdtable *fdt;
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if ((flags & ~O_CLOEXEC) != 0)
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return -EINVAL;
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if (unlikely(oldfd == newfd))
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return -EINVAL;
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spin_lock(&files->file_lock);
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err = expand_files(files, newfd);
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file = fcheck(oldfd);
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if (unlikely(!file))
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goto Ebadf;
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if (unlikely(err < 0)) {
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if (err == -EMFILE)
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goto Ebadf;
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goto out_unlock;
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}
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/*
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* We need to detect attempts to do dup2() over allocated but still
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* not finished descriptor. NB: OpenBSD avoids that at the price of
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* extra work in their equivalent of fget() - they insert struct
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* file immediately after grabbing descriptor, mark it larval if
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* more work (e.g. actual opening) is needed and make sure that
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* fget() treats larval files as absent. Potentially interesting,
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* but while extra work in fget() is trivial, locking implications
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* and amount of surgery on open()-related paths in VFS are not.
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* FreeBSD fails with -EBADF in the same situation, NetBSD "solution"
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* deadlocks in rather amusing ways, AFAICS. All of that is out of
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* scope of POSIX or SUS, since neither considers shared descriptor
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* tables and this condition does not arise without those.
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*/
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err = -EBUSY;
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fdt = files_fdtable(files);
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tofree = fdt->fd[newfd];
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if (!tofree && FD_ISSET(newfd, fdt->open_fds))
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goto out_unlock;
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get_file(file);
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rcu_assign_pointer(fdt->fd[newfd], file);
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FD_SET(newfd, fdt->open_fds);
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if (flags & O_CLOEXEC)
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FD_SET(newfd, fdt->close_on_exec);
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else
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FD_CLR(newfd, fdt->close_on_exec);
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spin_unlock(&files->file_lock);
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if (tofree)
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filp_close(tofree, files);
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return newfd;
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Ebadf:
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err = -EBADF;
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out_unlock:
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spin_unlock(&files->file_lock);
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return err;
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}
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SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd)
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{
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if (unlikely(newfd == oldfd)) { /* corner case */
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struct files_struct *files = current->files;
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int retval = oldfd;
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rcu_read_lock();
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if (!fcheck_files(files, oldfd))
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retval = -EBADF;
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rcu_read_unlock();
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return retval;
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}
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return sys_dup3(oldfd, newfd, 0);
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}
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SYSCALL_DEFINE1(dup, unsigned int, fildes)
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{
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int ret = -EBADF;
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struct file *file = fget(fildes);
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if (file) {
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ret = get_unused_fd();
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if (ret >= 0)
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fd_install(ret, file);
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else
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fput(file);
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}
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return ret;
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}
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#define SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT | O_NOATIME)
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static int setfl(int fd, struct file * filp, unsigned long arg)
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{
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struct inode * inode = filp->f_path.dentry->d_inode;
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int error = 0;
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/*
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* O_APPEND cannot be cleared if the file is marked as append-only
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* and the file is open for write.
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*/
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if (((arg ^ filp->f_flags) & O_APPEND) && IS_APPEND(inode))
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return -EPERM;
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/* O_NOATIME can only be set by the owner or superuser */
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if ((arg & O_NOATIME) && !(filp->f_flags & O_NOATIME))
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if (!is_owner_or_cap(inode))
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return -EPERM;
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/* required for strict SunOS emulation */
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if (O_NONBLOCK != O_NDELAY)
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if (arg & O_NDELAY)
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arg |= O_NONBLOCK;
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if (arg & O_DIRECT) {
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if (!filp->f_mapping || !filp->f_mapping->a_ops ||
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!filp->f_mapping->a_ops->direct_IO)
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return -EINVAL;
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}
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if (filp->f_op && filp->f_op->check_flags)
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error = filp->f_op->check_flags(arg);
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if (error)
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return error;
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/*
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* ->fasync() is responsible for setting the FASYNC bit.
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*/
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if (((arg ^ filp->f_flags) & FASYNC) && filp->f_op &&
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filp->f_op->fasync) {
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error = filp->f_op->fasync(fd, filp, (arg & FASYNC) != 0);
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if (error < 0)
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goto out;
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if (error > 0)
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error = 0;
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}
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spin_lock(&filp->f_lock);
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filp->f_flags = (arg & SETFL_MASK) | (filp->f_flags & ~SETFL_MASK);
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spin_unlock(&filp->f_lock);
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out:
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return error;
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}
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static void f_modown(struct file *filp, struct pid *pid, enum pid_type type,
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int force)
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{
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write_lock_irq(&filp->f_owner.lock);
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if (force || !filp->f_owner.pid) {
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put_pid(filp->f_owner.pid);
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filp->f_owner.pid = get_pid(pid);
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filp->f_owner.pid_type = type;
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if (pid) {
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const struct cred *cred = current_cred();
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filp->f_owner.uid = cred->uid;
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filp->f_owner.euid = cred->euid;
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}
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}
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write_unlock_irq(&filp->f_owner.lock);
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}
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int __f_setown(struct file *filp, struct pid *pid, enum pid_type type,
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int force)
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{
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int err;
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err = security_file_set_fowner(filp);
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if (err)
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return err;
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f_modown(filp, pid, type, force);
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return 0;
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}
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EXPORT_SYMBOL(__f_setown);
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int f_setown(struct file *filp, unsigned long arg, int force)
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{
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enum pid_type type;
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struct pid *pid;
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int who = arg;
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int result;
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type = PIDTYPE_PID;
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if (who < 0) {
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type = PIDTYPE_PGID;
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who = -who;
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}
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rcu_read_lock();
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pid = find_vpid(who);
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result = __f_setown(filp, pid, type, force);
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rcu_read_unlock();
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return result;
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}
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EXPORT_SYMBOL(f_setown);
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void f_delown(struct file *filp)
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{
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f_modown(filp, NULL, PIDTYPE_PID, 1);
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}
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pid_t f_getown(struct file *filp)
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{
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pid_t pid;
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read_lock(&filp->f_owner.lock);
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pid = pid_vnr(filp->f_owner.pid);
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if (filp->f_owner.pid_type == PIDTYPE_PGID)
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pid = -pid;
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read_unlock(&filp->f_owner.lock);
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return pid;
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}
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static int f_setown_ex(struct file *filp, unsigned long arg)
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{
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struct f_owner_ex * __user owner_p = (void * __user)arg;
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struct f_owner_ex owner;
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struct pid *pid;
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int type;
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int ret;
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ret = copy_from_user(&owner, owner_p, sizeof(owner));
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if (ret)
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return ret;
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switch (owner.type) {
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case F_OWNER_TID:
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type = PIDTYPE_MAX;
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break;
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case F_OWNER_PID:
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type = PIDTYPE_PID;
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break;
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case F_OWNER_PGRP:
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type = PIDTYPE_PGID;
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break;
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default:
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return -EINVAL;
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}
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rcu_read_lock();
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pid = find_vpid(owner.pid);
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if (owner.pid && !pid)
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ret = -ESRCH;
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else
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ret = __f_setown(filp, pid, type, 1);
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rcu_read_unlock();
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return ret;
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}
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static int f_getown_ex(struct file *filp, unsigned long arg)
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{
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struct f_owner_ex * __user owner_p = (void * __user)arg;
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struct f_owner_ex owner;
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int ret = 0;
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read_lock(&filp->f_owner.lock);
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owner.pid = pid_vnr(filp->f_owner.pid);
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switch (filp->f_owner.pid_type) {
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case PIDTYPE_MAX:
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owner.type = F_OWNER_TID;
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break;
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case PIDTYPE_PID:
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owner.type = F_OWNER_PID;
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break;
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case PIDTYPE_PGID:
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owner.type = F_OWNER_PGRP;
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break;
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default:
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WARN_ON(1);
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ret = -EINVAL;
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break;
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}
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read_unlock(&filp->f_owner.lock);
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if (!ret)
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ret = copy_to_user(owner_p, &owner, sizeof(owner));
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return ret;
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}
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static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
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struct file *filp)
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{
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long err = -EINVAL;
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switch (cmd) {
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case F_DUPFD:
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case F_DUPFD_CLOEXEC:
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if (arg >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
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break;
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err = alloc_fd(arg, cmd == F_DUPFD_CLOEXEC ? O_CLOEXEC : 0);
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if (err >= 0) {
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get_file(filp);
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fd_install(err, filp);
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}
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break;
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case F_GETFD:
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err = get_close_on_exec(fd) ? FD_CLOEXEC : 0;
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break;
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case F_SETFD:
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err = 0;
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set_close_on_exec(fd, arg & FD_CLOEXEC);
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break;
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case F_GETFL:
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err = filp->f_flags;
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break;
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case F_SETFL:
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err = setfl(fd, filp, arg);
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break;
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case F_GETLK:
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err = fcntl_getlk(filp, (struct flock __user *) arg);
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break;
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case F_SETLK:
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case F_SETLKW:
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err = fcntl_setlk(fd, filp, cmd, (struct flock __user *) arg);
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break;
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case F_GETOWN:
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/*
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* XXX If f_owner is a process group, the
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* negative return value will get converted
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* into an error. Oops. If we keep the
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* current syscall conventions, the only way
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* to fix this will be in libc.
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*/
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err = f_getown(filp);
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force_successful_syscall_return();
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break;
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case F_SETOWN:
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err = f_setown(filp, arg, 1);
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break;
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case F_GETOWN_EX:
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err = f_getown_ex(filp, arg);
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break;
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case F_SETOWN_EX:
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err = f_setown_ex(filp, arg);
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break;
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case F_GETSIG:
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err = filp->f_owner.signum;
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break;
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case F_SETSIG:
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/* arg == 0 restores default behaviour. */
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if (!valid_signal(arg)) {
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break;
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}
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err = 0;
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filp->f_owner.signum = arg;
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break;
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case F_GETLEASE:
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err = fcntl_getlease(filp);
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break;
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case F_SETLEASE:
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err = fcntl_setlease(fd, filp, arg);
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break;
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case F_NOTIFY:
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err = fcntl_dirnotify(fd, filp, arg);
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break;
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default:
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break;
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}
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return err;
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}
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SYSCALL_DEFINE3(fcntl, unsigned int, fd, unsigned int, cmd, unsigned long, arg)
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{
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struct file *filp;
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long err = -EBADF;
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filp = fget(fd);
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if (!filp)
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goto out;
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err = security_file_fcntl(filp, cmd, arg);
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if (err) {
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fput(filp);
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return err;
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}
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err = do_fcntl(fd, cmd, arg, filp);
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fput(filp);
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out:
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return err;
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}
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#if BITS_PER_LONG == 32
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SYSCALL_DEFINE3(fcntl64, unsigned int, fd, unsigned int, cmd,
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unsigned long, arg)
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{
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struct file * filp;
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long err;
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err = -EBADF;
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filp = fget(fd);
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if (!filp)
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goto out;
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err = security_file_fcntl(filp, cmd, arg);
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if (err) {
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fput(filp);
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return err;
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}
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err = -EBADF;
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switch (cmd) {
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case F_GETLK64:
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err = fcntl_getlk64(filp, (struct flock64 __user *) arg);
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break;
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case F_SETLK64:
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case F_SETLKW64:
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err = fcntl_setlk64(fd, filp, cmd,
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(struct flock64 __user *) arg);
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break;
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default:
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err = do_fcntl(fd, cmd, arg, filp);
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break;
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}
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fput(filp);
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out:
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return err;
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}
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#endif
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/* Table to convert sigio signal codes into poll band bitmaps */
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static const long band_table[NSIGPOLL] = {
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POLLIN | POLLRDNORM, /* POLL_IN */
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POLLOUT | POLLWRNORM | POLLWRBAND, /* POLL_OUT */
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POLLIN | POLLRDNORM | POLLMSG, /* POLL_MSG */
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POLLERR, /* POLL_ERR */
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POLLPRI | POLLRDBAND, /* POLL_PRI */
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POLLHUP | POLLERR /* POLL_HUP */
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};
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static inline int sigio_perm(struct task_struct *p,
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struct fown_struct *fown, int sig)
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{
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const struct cred *cred;
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int ret;
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rcu_read_lock();
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cred = __task_cred(p);
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ret = ((fown->euid == 0 ||
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fown->euid == cred->suid || fown->euid == cred->uid ||
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fown->uid == cred->suid || fown->uid == cred->uid) &&
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!security_file_send_sigiotask(p, fown, sig));
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rcu_read_unlock();
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return ret;
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}
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static void send_sigio_to_task(struct task_struct *p,
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struct fown_struct *fown,
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int fd, int reason, int group)
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{
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|
/*
|
|
* F_SETSIG can change ->signum lockless in parallel, make
|
|
* sure we read it once and use the same value throughout.
|
|
*/
|
|
int signum = ACCESS_ONCE(fown->signum);
|
|
|
|
if (!sigio_perm(p, fown, signum))
|
|
return;
|
|
|
|
switch (signum) {
|
|
siginfo_t si;
|
|
default:
|
|
/* Queue a rt signal with the appropriate fd as its
|
|
value. We use SI_SIGIO as the source, not
|
|
SI_KERNEL, since kernel signals always get
|
|
delivered even if we can't queue. Failure to
|
|
queue in this case _should_ be reported; we fall
|
|
back to SIGIO in that case. --sct */
|
|
si.si_signo = signum;
|
|
si.si_errno = 0;
|
|
si.si_code = reason;
|
|
/* Make sure we are called with one of the POLL_*
|
|
reasons, otherwise we could leak kernel stack into
|
|
userspace. */
|
|
BUG_ON((reason & __SI_MASK) != __SI_POLL);
|
|
if (reason - POLL_IN >= NSIGPOLL)
|
|
si.si_band = ~0L;
|
|
else
|
|
si.si_band = band_table[reason - POLL_IN];
|
|
si.si_fd = fd;
|
|
if (!do_send_sig_info(signum, &si, p, group))
|
|
break;
|
|
/* fall-through: fall back on the old plain SIGIO signal */
|
|
case 0:
|
|
do_send_sig_info(SIGIO, SEND_SIG_PRIV, p, group);
|
|
}
|
|
}
|
|
|
|
void send_sigio(struct fown_struct *fown, int fd, int band)
|
|
{
|
|
struct task_struct *p;
|
|
enum pid_type type;
|
|
struct pid *pid;
|
|
int group = 1;
|
|
|
|
read_lock(&fown->lock);
|
|
|
|
type = fown->pid_type;
|
|
if (type == PIDTYPE_MAX) {
|
|
group = 0;
|
|
type = PIDTYPE_PID;
|
|
}
|
|
|
|
pid = fown->pid;
|
|
if (!pid)
|
|
goto out_unlock_fown;
|
|
|
|
read_lock(&tasklist_lock);
|
|
do_each_pid_task(pid, type, p) {
|
|
send_sigio_to_task(p, fown, fd, band, group);
|
|
} while_each_pid_task(pid, type, p);
|
|
read_unlock(&tasklist_lock);
|
|
out_unlock_fown:
|
|
read_unlock(&fown->lock);
|
|
}
|
|
|
|
static void send_sigurg_to_task(struct task_struct *p,
|
|
struct fown_struct *fown, int group)
|
|
{
|
|
if (sigio_perm(p, fown, SIGURG))
|
|
do_send_sig_info(SIGURG, SEND_SIG_PRIV, p, group);
|
|
}
|
|
|
|
int send_sigurg(struct fown_struct *fown)
|
|
{
|
|
struct task_struct *p;
|
|
enum pid_type type;
|
|
struct pid *pid;
|
|
int group = 1;
|
|
int ret = 0;
|
|
|
|
read_lock(&fown->lock);
|
|
|
|
type = fown->pid_type;
|
|
if (type == PIDTYPE_MAX) {
|
|
group = 0;
|
|
type = PIDTYPE_PID;
|
|
}
|
|
|
|
pid = fown->pid;
|
|
if (!pid)
|
|
goto out_unlock_fown;
|
|
|
|
ret = 1;
|
|
|
|
read_lock(&tasklist_lock);
|
|
do_each_pid_task(pid, type, p) {
|
|
send_sigurg_to_task(p, fown, group);
|
|
} while_each_pid_task(pid, type, p);
|
|
read_unlock(&tasklist_lock);
|
|
out_unlock_fown:
|
|
read_unlock(&fown->lock);
|
|
return ret;
|
|
}
|
|
|
|
static DEFINE_RWLOCK(fasync_lock);
|
|
static struct kmem_cache *fasync_cache __read_mostly;
|
|
|
|
/*
|
|
* Remove a fasync entry. If successfully removed, return
|
|
* positive and clear the FASYNC flag. If no entry exists,
|
|
* do nothing and return 0.
|
|
*
|
|
* NOTE! It is very important that the FASYNC flag always
|
|
* match the state "is the filp on a fasync list".
|
|
*
|
|
* We always take the 'filp->f_lock', in since fasync_lock
|
|
* needs to be irq-safe.
|
|
*/
|
|
static int fasync_remove_entry(struct file *filp, struct fasync_struct **fapp)
|
|
{
|
|
struct fasync_struct *fa, **fp;
|
|
int result = 0;
|
|
|
|
spin_lock(&filp->f_lock);
|
|
write_lock_irq(&fasync_lock);
|
|
for (fp = fapp; (fa = *fp) != NULL; fp = &fa->fa_next) {
|
|
if (fa->fa_file != filp)
|
|
continue;
|
|
*fp = fa->fa_next;
|
|
kmem_cache_free(fasync_cache, fa);
|
|
filp->f_flags &= ~FASYNC;
|
|
result = 1;
|
|
break;
|
|
}
|
|
write_unlock_irq(&fasync_lock);
|
|
spin_unlock(&filp->f_lock);
|
|
return result;
|
|
}
|
|
|
|
/*
|
|
* Add a fasync entry. Return negative on error, positive if
|
|
* added, and zero if did nothing but change an existing one.
|
|
*
|
|
* NOTE! It is very important that the FASYNC flag always
|
|
* match the state "is the filp on a fasync list".
|
|
*/
|
|
static int fasync_add_entry(int fd, struct file *filp, struct fasync_struct **fapp)
|
|
{
|
|
struct fasync_struct *new, *fa, **fp;
|
|
int result = 0;
|
|
|
|
new = kmem_cache_alloc(fasync_cache, GFP_KERNEL);
|
|
if (!new)
|
|
return -ENOMEM;
|
|
|
|
spin_lock(&filp->f_lock);
|
|
write_lock_irq(&fasync_lock);
|
|
for (fp = fapp; (fa = *fp) != NULL; fp = &fa->fa_next) {
|
|
if (fa->fa_file != filp)
|
|
continue;
|
|
fa->fa_fd = fd;
|
|
kmem_cache_free(fasync_cache, new);
|
|
goto out;
|
|
}
|
|
|
|
new->magic = FASYNC_MAGIC;
|
|
new->fa_file = filp;
|
|
new->fa_fd = fd;
|
|
new->fa_next = *fapp;
|
|
*fapp = new;
|
|
result = 1;
|
|
filp->f_flags |= FASYNC;
|
|
|
|
out:
|
|
write_unlock_irq(&fasync_lock);
|
|
spin_unlock(&filp->f_lock);
|
|
return result;
|
|
}
|
|
|
|
/*
|
|
* fasync_helper() is used by almost all character device drivers
|
|
* to set up the fasync queue, and for regular files by the file
|
|
* lease code. It returns negative on error, 0 if it did no changes
|
|
* and positive if it added/deleted the entry.
|
|
*/
|
|
int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fapp)
|
|
{
|
|
if (!on)
|
|
return fasync_remove_entry(filp, fapp);
|
|
return fasync_add_entry(fd, filp, fapp);
|
|
}
|
|
|
|
EXPORT_SYMBOL(fasync_helper);
|
|
|
|
void __kill_fasync(struct fasync_struct *fa, int sig, int band)
|
|
{
|
|
while (fa) {
|
|
struct fown_struct * fown;
|
|
if (fa->magic != FASYNC_MAGIC) {
|
|
printk(KERN_ERR "kill_fasync: bad magic number in "
|
|
"fasync_struct!\n");
|
|
return;
|
|
}
|
|
fown = &fa->fa_file->f_owner;
|
|
/* Don't send SIGURG to processes which have not set a
|
|
queued signum: SIGURG has its own default signalling
|
|
mechanism. */
|
|
if (!(sig == SIGURG && fown->signum == 0))
|
|
send_sigio(fown, fa->fa_fd, band);
|
|
fa = fa->fa_next;
|
|
}
|
|
}
|
|
|
|
EXPORT_SYMBOL(__kill_fasync);
|
|
|
|
void kill_fasync(struct fasync_struct **fp, int sig, int band)
|
|
{
|
|
/* First a quick test without locking: usually
|
|
* the list is empty.
|
|
*/
|
|
if (*fp) {
|
|
read_lock(&fasync_lock);
|
|
/* reread *fp after obtaining the lock */
|
|
__kill_fasync(*fp, sig, band);
|
|
read_unlock(&fasync_lock);
|
|
}
|
|
}
|
|
EXPORT_SYMBOL(kill_fasync);
|
|
|
|
static int __init fasync_init(void)
|
|
{
|
|
fasync_cache = kmem_cache_create("fasync_cache",
|
|
sizeof(struct fasync_struct), 0, SLAB_PANIC, NULL);
|
|
return 0;
|
|
}
|
|
|
|
module_init(fasync_init)
|