| From caea1e58db9848b12b0cf7a0d70250bff9b59bd6 Mon Sep 17 00:00:00 2001 |
| From: Eric Sandeen <sandeen@redhat.com> |
| Date: Wed, 17 Jun 2020 14:19:04 -0500 |
| Subject: [PATCH] ext4: fix potential negative array index in do_split() |
| |
| commit 5872331b3d91820e14716632ebb56b1399b34fe1 upstream. |
| |
| 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: Paul Gortmaker <paul.gortmaker@windriver.com> |
| |
| diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c |
| index 7f1cb46f4f0d..8e1d5912556a 100644 |
| --- a/fs/ext4/namei.c |
| +++ b/fs/ext4/namei.c |
| @@ -1853,7 +1853,7 @@ 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--) { |
| @@ -1863,8 +1863,18 @@ 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", |
| -- |
| 2.27.0 |
| |