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[050/104] xfs: Fix possible memory corruption in xfs_readlink

To: <linux-kernel@xxxxxxxxxxxxxxx>, <stable@xxxxxxxxxxxxxxx>, greg@xxxxxxxxx
Subject: [050/104] xfs: Fix possible memory corruption in xfs_readlink
From: Greg KH <gregkh@xxxxxxx>
Date: Wed, 07 Dec 2011 08:11:52 -0800
Cc: <torvalds@xxxxxxxxxxxxxxxxxxxx>, <akpm@xxxxxxxxxxxxxxxxxxxx>, <alan@xxxxxxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, bpm@xxxxxxx, Carlos Maiolino <cmaiolino@xxxxxxxxxx>, Alex Elder <aelder@xxxxxxx>
In-reply-to: <20111207161246.GA10995@xxxxxxxxx>
User-agent: quilt/0.50-23.1
3.1-stable 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>
Cc: Ben Myers <bpm@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
---
 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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