From: Eric Sandeen <sandeen@redhat.com>
To: "linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>
Subject: [PATCH 1/1] ext4: fix potential negative array index in do_split()
Date: Wed, 17 Jun 2020 14:19:04 -0500 [thread overview]
Message-ID: <f53e246b-647c-64bb-16ec-135383c70ad7@redhat.com> (raw)
In-Reply-To: <d08d63e9-8f74-b571-07c7-828b9629ce6a@redhat.com>
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>
---
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",
next prev parent reply other threads:[~2020-06-17 19:19 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-17 19:01 [PATCH 0/1] ext4: fix potential negative array index in do_split Eric Sandeen
2020-06-17 19:19 ` Eric Sandeen [this message]
2020-06-19 0:33 ` [PATCH 1/1] ext4: fix potential negative array index in do_split() Andreas Dilger
2020-06-19 6:41 ` Lukas Czerner
2020-06-19 7:08 ` Lukas Czerner
2020-06-19 11:16 ` Lukas Czerner
2020-06-19 13:44 ` Eric Sandeen
2020-06-19 13:53 ` Lukas Czerner
2020-06-19 13:42 ` Eric Sandeen
2020-06-19 13:49 ` Lukas Czerner
2020-06-19 13:39 ` Eric Sandeen
2020-07-08 16:09 ` Jan Kara
2020-07-30 1:48 ` tytso
2020-06-19 2:31 ` [PATCH 0/1] ext4: fix potential negative array index in do_split Andreas Dilger
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