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@xxxxxxxxxx>
---
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index a8aca4772aaa..8b60881f07ee 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -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 */
- 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",
