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ext4: fix potential negative array index in do_split()

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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: ef2b02d3e6 ("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>
This commit is contained in:
Eric Sandeen 2020-06-17 14:19:04 -05:00 • committed by Theodore Ts'o
parent 24dc986491
commit 5872331b3d
1 changed files with 13 additions and 3 deletions
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14
fs/ext4/namei.c
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@ -1858,7 +1858,7 @@ static struct ext4_dir_entry_2 *do_split(handle_t *handle, struct inode *dir,
blocksize, hinfo, map); blocksize, hinfo, map);
map -= count; map -= count;
dx_sort_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; size = 0;
move = 0; move = 0;
for (i = count-1; i >= 0; i--) { 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; size += map[i].size;
move++; move++;
} }
/* map index at which we will split */ /*
* 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; split = count - move;
else
split = count/2;
hash2 = map[split].hash; hash2 = map[split].hash;
continued = hash2 == map[split - 1].hash; continued = hash2 == map[split - 1].hash;
dxtrace(printk(KERN_INFO "Split block %lu at %x, %i/%i\n", dxtrace(printk(KERN_INFO "Split block %lu at %x, %i/%i\n",