Commit 5872331b authored Jun 17, 2020 by Eric Sandeen Committed by Theodore Ts'o Aug 06, 2020

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: ef2b02d3 ("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>

parent 24dc9864

fs/ext4/namei.c

+13 −3

Original line number	Diff line number	Diff line
		@@ -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 */
		/*
		* 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",

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