[XFS] truncate readdir offsets to signed 32 bit values

John Stanley reported EOVERFLOW errors in readdir from his self-build
glibc.  I traced this down to glibc enabling d_off overflow checks
in one of the about five million different getdents implementations.

In 2.6.28 Dave Woodhouse moved our readdir double buffering required
for NFS4 readdirplus into nfsd and at that point we lost the capping
of the directory offsets to 32 bit signed values.  Johns glibc used
getdents64 to even implement readdir for normal 32 bit offset dirents,
and failed with EOVERFLOW only if this happens on the first dirent in
a getdents call.  I managed to come up with a testcase that uses
raw getdents and does the EOVERFLOW check manually.  We always hit
it with our last entry due to the special end of directory marker.

The patch below is a dumb version of just putting back the masking,
to make sure we have the same behavior as in 2.6.27 and earlier.

I will work on a better and cleaner fix for 2.6.30.

Reported-by: John Stanley <jpsinthemix@verizon.net>
Tested-by: John Stanley <jpsinthemix@verizon.net>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/fs/xfs/xfs_dir2_block.c b/fs/xfs/xfs_dir2_block.c
index e2fa0a1d8e96..e1f0a06aaf04 100644
--- a/fs/xfs/xfs_dir2_block.c
+++ b/fs/xfs/xfs_dir2_block.c
@@ -517,9 +517,9 @@ xfs_dir2_block_getdents(
                 /*
                  * If it didn't fit, set the final offset to here & return.
                  */
-                if (filldir(dirent, dep->name, dep->namelen, cook,
+                if (filldir(dirent, dep->name, dep->namelen, cook & 0x7fffffff,
                             ino, DT_UNKNOWN)) {
-                        *offset = cook;
+                        *offset = cook & 0x7fffffff;
                         xfs_da_brelse(NULL, bp);
                         return 0;
                 }
@@ -529,7 +529,8 @@ xfs_dir2_block_getdents(
          * Reached the end of the block.
          * Set the offset to a non-existent block 1 and return.
          */
-        *offset = xfs_dir2_db_off_to_dataptr(mp, mp->m_dirdatablk + 1, 0);
+        *offset = xfs_dir2_db_off_to_dataptr(mp, mp->m_dirdatablk + 1, 0) &
+                        0x7fffffff;
         xfs_da_brelse(NULL, bp);
         return 0;
 }