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futex: Do not leak robust list to unprivileged process 

It was possible to extract the robust list head address from a setuid
process if it had used set_robust_list(), allowing an ASLR info leak. This
changes the permission checks to be the same as those used for similar
info that comes out of /proc.

Running a setuid program that uses robust futexes would have had:
  cred->euid != pcred->euid
  cred->euid == pcred->uid
so the old permissions check would allow it. I'm not aware of any setuid
programs that use robust futexes, so this is just a preventative measure.

(This patch is based on changes from grsecurity.)

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Darren Hart <dvhart@linux.intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Serge E. Hallyn <serge.hallyn@canonical.com>
Cc: kernel-hardening@lists.openwall.com
Cc: spender@grsecurity.net
Link: http://lkml.kernel.org/r/20120319231253.GA20893@www.outflux.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Kees Cook 2012-03-19 16:12:53 -07:00 committed by Thomas Gleixner
parent b5174fa3a7
commit bdbb776f88
2 changed files with 28 additions and 48 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
kernel/futex.c
View File

@ -59,6 +59,7 @@
#include <linux/magic.h>
#include <linux/pid.h>
#include <linux/nsproxy.h>
#include <linux/ptrace.h>
#include <asm/futex.h>
@ -2443,40 +2444,29 @@ SYSCALL_DEFINE3(get_robust_list, int, pid,
{
struct robust_list_head __user *head;
unsigned long ret;
const struct cred *cred = current_cred(), *pcred;
struct task_struct *p;
if (!futex_cmpxchg_enabled)
return -ENOSYS;
if (!pid)
head = current->robust_list;
else {
struct task_struct *p;
rcu_read_lock();
ret = -ESRCH;
rcu_read_lock();
ret = -ESRCH;
if (!pid)
p = current;
else {
p = find_task_by_vpid(pid);
if (!p)
goto err_unlock;
ret = -EPERM;
pcred = __task_cred(p);
/* If victim is in different user_ns, then uids are not
comparable, so we must have CAP_SYS_PTRACE */
if (cred->user->user_ns != pcred->user->user_ns) {
if (!ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))
goto err_unlock;
goto ok;
}
/* If victim is in same user_ns, then uids are comparable */
if (cred->euid != pcred->euid &&
cred->euid != pcred->uid &&
!ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))
goto err_unlock;
ok:
head = p->robust_list;
rcu_read_unlock();
}
ret = -EPERM;
if (!ptrace_may_access(p, PTRACE_MODE_READ))
goto err_unlock;
head = p->robust_list;
rcu_read_unlock();
if (put_user(sizeof(*head), len_ptr))
return -EFAULT;
return put_user(head, head_ptr);

38
kernel/futex_compat.c
View File

@ -10,6 +10,7 @@
#include <linux/compat.h>
#include <linux/nsproxy.h>
#include <linux/futex.h>
#include <linux/ptrace.h>
#include <asm/uaccess.h>
@ -136,40 +137,29 @@ compat_sys_get_robust_list(int pid, compat_uptr_t __user *head_ptr,
{
struct compat_robust_list_head __user *head;
unsigned long ret;
const struct cred *cred = current_cred(), *pcred;
struct task_struct *p;
if (!futex_cmpxchg_enabled)
return -ENOSYS;
if (!pid)
head = current->compat_robust_list;
else {
struct task_struct *p;
rcu_read_lock();
ret = -ESRCH;
rcu_read_lock();
ret = -ESRCH;
if (!pid)
p = current;
else {
p = find_task_by_vpid(pid);
if (!p)
goto err_unlock;
ret = -EPERM;
pcred = __task_cred(p);
/* If victim is in different user_ns, then uids are not
comparable, so we must have CAP_SYS_PTRACE */
if (cred->user->user_ns != pcred->user->user_ns) {
if (!ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))
goto err_unlock;
goto ok;
}
/* If victim is in same user_ns, then uids are comparable */
if (cred->euid != pcred->euid &&
cred->euid != pcred->uid &&
!ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))
goto err_unlock;
ok:
head = p->compat_robust_list;
rcu_read_unlock();
}
ret = -EPERM;
if (!ptrace_may_access(p, PTRACE_MODE_READ))
goto err_unlock;
head = p->compat_robust_list;
rcu_read_unlock();
if (put_user(sizeof(*head), len_ptr))
return -EFAULT;
return put_user(ptr_to_compat(head), head_ptr);