[ 046/180] xfs: Fix possible memory corruption in xfs_readlink

[Willy Tarreau]

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

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

From: Carlos Maiolino <cmaiolino@xxxxxxxxxx>

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@xxxxxxx>
Signed-off-by: Carlos Maiolino <cmaiolino@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
[dannf: backported to Debian's 2.6.32]
Signed-off-by: Willy Tarreau <w@xxxxxx>
---
 fs/xfs/xfs_vnodeops.c |   15 +++++++++++----
 1 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/xfs_vnodeops.c b/fs/xfs/xfs_vnodeops.c
index 8f32f50..1638884 100644
--- a/fs/xfs/xfs_vnodeops.c
+++ b/fs/xfs/xfs_vnodeops.c
@@ -554,7 +554,7 @@ xfs_readlink(
 	char		*link)
 {
 	xfs_mount_t	*mp = ip->i_mount;
-	int		pathlen;
+	xfs_fsize_t	pathlen;
 	int		error = 0;
 
 	xfs_itrace_entry(ip);
@@ -564,13 +564,20 @@ xfs_readlink(
 
 	xfs_ilock(ip, XFS_ILOCK_SHARED);
 
-	ASSERT((ip->i_d.di_mode & S_IFMT) == S_IFLNK);
-	ASSERT(ip->i_d.di_size <= MAXPATHLEN);
-
 	pathlen = ip->i_d.di_size;
 	if (!pathlen)
 		goto out;
 
+	if (pathlen < 0 || pathlen > MAXPATHLEN) {
+		xfs_fs_cmn_err(CE_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';
-- 
1.7.2.1.45.g54fbc



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