xfs: Fix possible memory corruption in xfs_readlink

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>

1 files changed, 10 insertions, 4 deletions

diff --git a/fs/xfs/xfs_vnodeops.c b/fs/xfs/xfs_vnodeops.c
index 4ecf2a549060..ce9268a2f56b 100644
--- a/fs/xfs/xfs_vnodeops.c
+++ b/fs/xfs/xfs_vnodeops.c
@@ -112,7 +112,7 @@ xfs_readlink(
         char            *link)
 {
         xfs_mount_t     *mp = ip->i_mount;
-        int             pathlen;
+        xfs_fsize_t     pathlen;
         int             error = 0;
 
         trace_xfs_readlink(ip);
@@ -122,13 +122,19 @@ 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';