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authorEric Sandeen <sandeen@redhat.com>2017-04-13 15:15:47 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-06-07 12:07:51 +0200
commit93bd169845e5d5911e51509d7c7e4cba4a3a2d5a (patch)
tree6ef7cc52b7f7ae8108178d4c873ce83e2c7792bb
parent99226b890d63c5aaf8b5ccc95b17d1a8087f45c9 (diff)
downloadlinux-aarch64-93bd169845e5d5911e51509d7c7e4cba4a3a2d5a.tar.gz
xfs: handle array index overrun in xfs_dir2_leaf_readbuf()
commit 023cc840b40fad95c6fe26fff1d380a8c9d45939 upstream. Carlos had a case where "find" seemed to start spinning forever and never return. This was on a filesystem with non-default multi-fsb (8k) directory blocks, and a fragmented directory with extents like this: 0:[0,133646,2,0] 1:[2,195888,1,0] 2:[3,195890,1,0] 3:[4,195892,1,0] 4:[5,195894,1,0] 5:[6,195896,1,0] 6:[7,195898,1,0] 7:[8,195900,1,0] 8:[9,195902,1,0] 9:[10,195908,1,0] 10:[11,195910,1,0] 11:[12,195912,1,0] 12:[13,195914,1,0] ... i.e. the first extent is a contiguous 2-fsb dir block, but after that it is fragmented into 1 block extents. At the top of the readdir path, we allocate a mapping array which (for this filesystem geometry) can hold 10 extents; see the assignment to map_info->map_size. During readdir, we are therefore able to map extents 0 through 9 above into the array for readahead purposes. If we count by 2, we see that the last mapped index (9) is the first block of a 2-fsb directory block. At the end of xfs_dir2_leaf_readbuf() we have 2 loops to fill more readahead; the outer loop assumes one full dir block is processed each loop iteration, and an inner loop that ensures that this is so by advancing to the next extent until a full directory block is mapped. The problem is that this inner loop may step past the last extent in the mapping array as it tries to reach the end of the directory block. This will read garbage for the extent length, and as a result the loop control variable 'j' may become corrupted and never fail the loop conditional. The number of valid mappings we have in our array is stored in map->map_valid, so stop this inner loop based on that limit. There is an ASSERT at the top of the outer loop for this same condition, but we never made it out of the inner loop, so the ASSERT never fired. Huge appreciation for Carlos for debugging and isolating the problem. Debugged-and-analyzed-by: Carlos Maiolino <cmaiolino@redhat.com> Signed-off-by: Eric Sandeen <sandeen@redhat.com> Tested-by: Carlos Maiolino <cmaiolino@redhat.com> Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com> Reviewed-by: Bill O'Donnell <billodo@redhat.com> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--fs/xfs/xfs_dir2_readdir.c10
1 files changed, 8 insertions, 2 deletions
diff --git a/fs/xfs/xfs_dir2_readdir.c b/fs/xfs/xfs_dir2_readdir.c
index 6645a221bf8e..ba95846f8f8a 100644
--- a/fs/xfs/xfs_dir2_readdir.c
+++ b/fs/xfs/xfs_dir2_readdir.c
@@ -394,6 +394,7 @@ xfs_dir2_leaf_readbuf(
/*
* Do we need more readahead?
+ * Each loop tries to process 1 full dir blk; last may be partial.
*/
blk_start_plug(&plug);
for (mip->ra_index = mip->ra_offset = i = 0;
@@ -425,9 +426,14 @@ xfs_dir2_leaf_readbuf(
}
/*
- * Advance offset through the mapping table.
+ * Advance offset through the mapping table, processing a full
+ * dir block even if it is fragmented into several extents.
+ * But stop if we have consumed all valid mappings, even if
+ * it's not yet a full directory block.
*/
- for (j = 0; j < geo->fsbcount; j += length ) {
+ for (j = 0;
+ j < geo->fsbcount && mip->ra_index < mip->map_valid;
+ j += length ) {
/*
* The rest of this extent but not more than a dir
* block.