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Btrfs: avoid buffer overrun in mount option handling

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There is an off-by-one error: allocating room for a maximal result
string but without room for a trailing NUL.  That, can lead to
returning a transformed string that is not NUL-terminated, and
then to a caller reading beyond end of the malloc'd buffer.

Rewrite to s/kzalloc/kmalloc/, remove unwarranted use of strncpy
(the result is guaranteed to fit), remove dead strlen at end, and
change a few variable names and comments.

Reviewed-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Jim Meyering <meyering@redhat.com>
This commit is contained in:
Jim Meyering 2012-04-25 21:24:17 +02:00 committed by Josef Bacik
parent a27202fbe9
commit f60d16a892
1 changed files with 26 additions and 41 deletions
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67
fs/btrfs/super.c
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@ -923,63 +923,48 @@ static inline int is_subvolume_inode(struct inode *inode)
*/
static char *setup_root_args(char *args)
{
unsigned copied = 0;
unsigned len = strlen(args) + 2;
char *pos;
char *ret;
unsigned len = strlen(args) + 2 + 1;
char *src, *dst, *buf;
/*
* We need the same args as before, but minus
* We need the same args as before, but with this substitution:
* s!subvol=[^,]+!subvolid=0!
*
* subvol=a
*
* and add
*
* subvolid=0
*
* which is a difference of 2 characters, so we allocate strlen(args) +
* 2 characters.
* Since the replacement string is up to 2 bytes longer than the
* original, allocate strlen(args) + 2 + 1 bytes.
*/
ret = kzalloc(len * sizeof(char), GFP_NOFS);
if (!ret)
return NULL;
pos = strstr(args, "subvol=");
src = strstr(args, "subvol=");
/* This shouldn't happen, but just in case.. */
if (!pos) {
kfree(ret);
if (!src)
return NULL;
buf = dst = kmalloc(len, GFP_NOFS);
if (!buf)
return NULL;
}
/*
* The subvol=<> arg is not at the front of the string, copy everybody
* up to that into ret.
* If the subvol= arg is not at the start of the string,
* copy whatever precedes it into buf.
*/
if (pos != args) {
*pos = '\0';
strcpy(ret, args);
copied += strlen(args);
pos++;
if (src != args) {
*src++ = '\0';
strcpy(buf, args);
dst += strlen(args);
}
strncpy(ret + copied, "subvolid=0", len - copied);
/* Length of subvolid=0 */
copied += 10;
strcpy(dst, "subvolid=0");
dst += strlen("subvolid=0");
/*
* If there is no , after the subvol= option then we know there's no
* other options and we can just return.
* If there is a "," after the original subvol=... string,
* copy that suffix into our buffer. Otherwise, we're done.
*/
pos = strchr(pos, ',');
if (!pos)
return ret;
src = strchr(src, ',');
if (src)
strcpy(dst, src);
/* Copy the rest of the arguments into our buffer */
strncpy(ret + copied, pos, len - copied);
copied += strlen(pos);
return ret;
return buf;
}
static struct dentry *mount_subvol(const char *subvol_name, int flags,