xfs: Fix possible memory corruption in xfs_readlink

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>
[PG: no xfs_alert in 2.6.34; use xfs_fs_cmn_err(CE_ALERT, ...) instead]
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/fs/xfs/xfs_vnodeops.c b/fs/xfs/xfs_vnodeops.c
index 4498f07e5a18b3550b9509b0207d5fdbf2859bf8..c682c5d8594a54c35ea421e2e17ca46c77904f6e 100644 (file)
--- 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 +564,19 @@ 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';