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vfs: introduce FMODE_UNSIGNED_OFFSET for allowing negative f_pos 

Now, rw_verify_area() checsk f_pos is negative or not.  And if negative,
returns -EINVAL.

But, some special files as /dev/(k)mem and /proc/<pid>/mem etc..  has
negative offsets.  And we can't do any access via read/write to the
file(device).

So introduce FMODE_UNSIGNED_OFFSET to allow negative file offsets.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
KAMEZAWA Hiroyuki 2010-10-01 14:20:22 -07:00 committed by Al Viro
parent ba10f48665
commit 4a3956c790
4 changed files with 33 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
drivers/char/mem.c
View File

@ -876,6 +876,10 @@ static int memory_open(struct inode *inode, struct file *filp)
if (dev->dev_info)
filp->f_mapping->backing_dev_info = dev->dev_info;
/* Is /dev/mem or /dev/kmem ? */
if (dev->dev_info == &directly_mappable_cdev_bdi)
filp->f_mode |= FMODE_UNSIGNED_OFFSET;
if (dev->fops->open)
return dev->fops->open(inode, filp);

2
fs/proc/base.c
View File

@ -771,6 +771,8 @@ static const struct file_operations proc_single_file_operations = {
static int mem_open(struct inode* inode, struct file* file)
{
file->private_data = (void*)((long)current->self_exec_id);
/* OK to pass negative loff_t, we can catch out-of-range */
file->f_mode |= FMODE_UNSIGNED_OFFSET;
return 0;
}

28
fs/read_write.c
View File

@ -31,6 +31,20 @@ const struct file_operations generic_ro_fops = {
EXPORT_SYMBOL(generic_ro_fops);
static int
__negative_fpos_check(struct file *file, loff_t pos, size_t count)
{
/*
* pos or pos+count is negative here, check overflow.
* too big "count" will be caught in rw_verify_area().
*/
if ((pos < 0) && (pos + count < pos))
return -EOVERFLOW;
if (file->f_mode & FMODE_UNSIGNED_OFFSET)
return 0;
return -EINVAL;
}
/**
* generic_file_llseek_unlocked - lockless generic llseek implementation
* @file: file structure to seek on
@ -62,7 +76,9 @@ generic_file_llseek_unlocked(struct file *file, loff_t offset, int origin)
break;
}
if (offset < 0 || offset > inode->i_sb->s_maxbytes)
if (offset < 0 && __negative_fpos_check(file, offset, 0))
return -EINVAL;
if (offset > inode->i_sb->s_maxbytes)
return -EINVAL;
/* Special lock needed here? */
@ -137,7 +153,7 @@ loff_t default_llseek(struct file *file, loff_t offset, int origin)
offset += file->f_pos;
}
retval = -EINVAL;
if (offset >= 0) {
if (offset >= 0 || !__negative_fpos_check(file, offset, 0)) {
if (offset != file->f_pos) {
file->f_pos = offset;
file->f_version = 0;
@ -221,6 +237,7 @@ bad:
}
#endif
/*
* rw_verify_area doesn't like huge counts. We limit
* them to something that fits in "int" so that others
@ -238,8 +255,11 @@ int rw_verify_area(int read_write, struct file *file, loff_t *ppos, size_t count
if (unlikely((ssize_t) count < 0))
return retval;
pos = *ppos;
if (unlikely((pos < 0) || (loff_t) (pos + count) < 0))
return retval;
if (unlikely((pos < 0) || (loff_t) (pos + count) < 0)) {
retval = __negative_fpos_check(file, pos, count);
if (retval)
return retval;
}
if (unlikely(inode->i_flock && mandatory_lock(inode))) {
retval = locks_mandatory_area(

3
include/linux/fs.h
View File

@ -92,6 +92,9 @@ struct inodes_stat_t {
/* Expect random access pattern */
#define FMODE_RANDOM ((__force fmode_t)0x1000)
/* File is huge (eg. /dev/kmem): treat loff_t as unsigned */
#define FMODE_UNSIGNED_OFFSET ((__force fmode_t)0x2000)
/* File was opened by fanotify and shouldn't generate fanotify events */
#define FMODE_NONOTIFY ((__force fmode_t)0x1000000)