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Subject[050/104] xfs: Fix possible memory corruption in xfs_readlink
3.1-stable review patch.  If anyone has any objections, please let me know.

------------------


From: Carlos Maiolino <cmaiolino@redhat.com>

commit b52a360b2aa1c59ba9970fb0f52bbb093fcc7a24 upstream.

Fixes a possible memory corruption when the link is larger than
MAXPATHLEN and XFS_DEBUG is not enabled. This also remove the
S_ISLNK assert, since the inode mode is checked previously in
xfs_readlink_by_handle() and via VFS.

Updated to address concerns raised by Ben Hutchings about the loose
attention paid to 32- vs 64-bit values, and the lack of handling a
potentially negative pathlen value:
- Changed type of "pathlen" to be xfs_fsize_t, to match that of
ip->i_d.di_size
- Added checking for a negative pathlen to the too-long pathlen
test, and generalized the message that gets reported in that case
to reflect the change
As a result, if a negative pathlen were encountered, this function
would return EFSCORRUPTED (and would fail an assertion for a debug
build)--just as would a too-long pathlen.

Signed-off-by: Alex Elder <aelder@sgi.com>
Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Ben Myers <bpm@sgi.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
fs/xfs/xfs_vnodeops.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)

--- a/fs/xfs/xfs_vnodeops.c
+++ b/fs/xfs/xfs_vnodeops.c
@@ -113,7 +113,7 @@ xfs_readlink(
char *link)
{
xfs_mount_t *mp = ip->i_mount;
- int pathlen;
+ xfs_fsize_t pathlen;
int error = 0;

trace_xfs_readlink(ip);
@@ -123,13 +123,19 @@ xfs_readlink(

xfs_ilock(ip, XFS_ILOCK_SHARED);

- ASSERT(S_ISLNK(ip->i_d.di_mode));
- ASSERT(ip->i_d.di_size <= MAXPATHLEN);
-
pathlen = ip->i_d.di_size;
if (!pathlen)
goto out;

+ if (pathlen < 0 || pathlen > MAXPATHLEN) {
+ xfs_alert(mp, "%s: inode (%llu) bad symlink length (%lld)",
+ __func__, (unsigned long long) ip->i_ino,
+ (long long) pathlen);
+ ASSERT(0);
+ return XFS_ERROR(EFSCORRUPTED);
+ }
+
+
if (ip->i_df.if_flags & XFS_IFINLINE) {
memcpy(link, ip->i_df.if_u1.if_data, pathlen);
link[pathlen] = '\0';



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