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Commit 539ae3e0 authored by Eric Sandeen's avatar Eric Sandeen Committed by Greg Kroah-Hartman
Browse files

ext4: fix potential negative array index in do_split() 



[ Upstream commit 5872331b3d91820e14716632ebb56b1399b34fe1 ]

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: ef2b02d3 ("ext34: ensure do_split leaves enough free space in both blocks")
Signed-off-by: default avatarEric Sandeen <sandeen@redhat.com>
Reviewed-by: default avatarAndreas Dilger <adilger@dilger.ca>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/f53e246b-647c-64bb-16ec-135383c70ad7@redhat.com


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent cc0c6b17

fs/ext4/namei.c

+13 −3
Original line number Diff line number Diff line
@@ -1759,7 +1759,7 @@ 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--) {
@@ -1769,8 +1769,18 @@ 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 */

	/*

	 * 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",