[PATCH, RFC] directory offset overflows in 2.6.28

[Christoph Hellwig <hch@infradead.org>]

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 think we should at least hide it in a macro that is well-commented,
but I suspect we also need to make sure that we never ever get bigger
offsets in directories in some way.


Index: xfs/fs/xfs/xfs_dir2_block.c
===================================================================
--- xfs.orig/fs/xfs/xfs_dir2_block.c	2008-12-29 21:25:29.680613664 +0100
+++ xfs/fs/xfs/xfs_dir2_block.c	2008-12-29 21:29:57.341627581 +0100
@@ -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;
 }
Index: xfs/fs/xfs/xfs_dir2_leaf.c
===================================================================
--- xfs.orig/fs/xfs/xfs_dir2_leaf.c	2008-12-29 21:25:13.899613482 +0100
+++ xfs/fs/xfs/xfs_dir2_leaf.c	2008-12-29 21:29:36.125616996 +0100
@@ -1092,7 +1092,7 @@ xfs_dir2_leaf_getdents(
 		 * Won't fit.  Return to caller.
 		 */
 		if (filldir(dirent, dep->name, dep->namelen,
-			    xfs_dir2_byte_to_dataptr(mp, curoff),
+			    xfs_dir2_byte_to_dataptr(mp, curoff) & 0x7fffffff,
 			    ino, DT_UNKNOWN))
 			break;
 
@@ -1108,9 +1108,9 @@ xfs_dir2_leaf_getdents(
 	 * All done.  Set output offset value to current offset.
 	 */
 	if (curoff > xfs_dir2_dataptr_to_byte(mp, XFS_DIR2_MAX_DATAPTR))
-		*offset = XFS_DIR2_MAX_DATAPTR;
+		*offset = XFS_DIR2_MAX_DATAPTR & 0x7fffffff;
 	else
-		*offset = xfs_dir2_byte_to_dataptr(mp, curoff);
+		*offset = xfs_dir2_byte_to_dataptr(mp, curoff) & 0x7fffffff;
 	kmem_free(map);
 	if (bp)
 		xfs_da_brelse(NULL, bp);
Index: xfs/fs/xfs/xfs_dir2_sf.c
===================================================================
--- xfs.orig/fs/xfs/xfs_dir2_sf.c	2008-12-29 21:23:55.174613820 +0100
+++ xfs/fs/xfs/xfs_dir2_sf.c	2008-12-29 21:29:00.721617384 +0100
@@ -752,8 +752,8 @@ xfs_dir2_sf_getdents(
 #if XFS_BIG_INUMS
 		ino += mp->m_inoadd;
 #endif
-		if (filldir(dirent, ".", 1, dot_offset, ino, DT_DIR)) {
-			*offset = dot_offset;
+		if (filldir(dirent, ".", 1, dot_offset & 0x7fffffff, ino, DT_DIR)) {
+			*offset = dot_offset & 0x7fffffff;
 			return 0;
 		}
 	}
@@ -766,8 +766,8 @@ xfs_dir2_sf_getdents(
 #if XFS_BIG_INUMS
 		ino += mp->m_inoadd;
 #endif
-		if (filldir(dirent, "..", 2, dotdot_offset, ino, DT_DIR)) {
-			*offset = dotdot_offset;
+		if (filldir(dirent, "..", 2, dotdot_offset & 0x7fffffff, ino, DT_DIR)) {
+			*offset = dotdot_offset & 0x7fffffff;
 			return 0;
 		}
 	}
@@ -791,14 +791,15 @@ xfs_dir2_sf_getdents(
 #endif
 
 		if (filldir(dirent, sfep->name, sfep->namelen,
-					    off, ino, DT_UNKNOWN)) {
-			*offset = off;
+			    off & 0x7fffffff, ino, DT_UNKNOWN)) {
+			*offset = off & 0x7fffffff;
 			return 0;
 		}
 		sfep = xfs_dir2_sf_nextentry(sfp, sfep);
 	}
 
-	*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;
 	return 0;
 }
 

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