From: Eric Sandeen sandeen@redhat.com
[ 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: 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 Signed-off-by: Sasha Levin sashal@kernel.org --- fs/ext4/namei.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c index 0218b1407abbb..36a81b57012a5 100644 --- a/fs/ext4/namei.c +++ b/fs/ext4/namei.c @@ -1852,7 +1852,7 @@ 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--) { @@ -1862,8 +1862,18 @@ 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",