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| author | Eric Sandeen <sandeen@redhat.com> | 2020-06-17 14:19:04 -0500 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2020-08-06 00:11:16 -0400 |
| commit | 5872331b3d91820e14716632ebb56b1399b34fe1 (patch) | |
| tree | 4f35152ee730e3ad04766cedebad6b0a336a3bd1 | |
| parent | 24dc9864914eb5813173cfa53313fcd02e4aea7d (diff) | |
| download | lwn-5872331b3d91820e14716632ebb56b1399b34fe1.tar.gz lwn-5872331b3d91820e14716632ebb56b1399b34fe1.zip | |
ext4: fix potential negative array index in do_split()
If for any reason a directory passed to do_split() does not have enough
active entries to exceed half the size of the block, we can end up
iterating over all "count" entries without finding a split point.
In this case, count == move, and split will be zero, and we will
attempt a negative index into map[].
Guard against this by detecting this case, and falling back to
split-to-half-of-count instead; in this case we will still have
plenty of space (> half blocksize) in each split block.
Fixes: ef2b02d3e617 ("ext34: ensure do_split leaves enough free space in both blocks")
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/f53e246b-647c-64bb-16ec-135383c70ad7@redhat.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
| -rw-r--r-- | fs/ext4/namei.c | 16 |
1 files changed, 13 insertions, 3 deletions
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c index 56738b538ddf..ef606301a106 100644 --- a/fs/ext4/namei.c +++ b/fs/ext4/namei.c @@ -1858,7 +1858,7 @@ static struct ext4_dir_entry_2 *do_split(handle_t *handle, struct inode *dir, blocksize, hinfo, map); map -= count; dx_sort_map(map, count); - /* Split the existing block in the middle, size-wise */ + /* Ensure that neither split block is over half full */ size = 0; move = 0; for (i = count-1; i >= 0; i--) { @@ -1868,8 +1868,18 @@ static struct ext4_dir_entry_2 *do_split(handle_t *handle, struct inode *dir, size += map[i].size; move++; } - /* map index at which we will split */ - split = count - move; + /* + * map index at which we will split + * + * If the sum of active entries didn't exceed half the block size, just + * split it in half by count; each resulting block will have at least + * half the space free. + */ + if (i > 0) + split = count - move; + else + split = count/2; + hash2 = map[split].hash; continued = hash2 == map[split - 1].hash; dxtrace(printk(KERN_INFO "Split block %lu at %x, %i/%i\n", |