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Re: [PATCH] btrfs: fix a NULL pointer dereference






On 2019/3/14 4:02 PM, Qu Wenruo wrote:


On 2019/3/14 下午3:54, Nikolay Borisov wrote:


On 14.03.19 г. 9:50 ч., Kangjie Lu wrote:
btrfs_lookup_block_group may fail and return NULL. The fix goes
to out when it fails to avoid NULL pointer dereference.

Actually no, in this case btrfs_lookup_block_group must never fail
because if we have an allocated eb then it must have been allocated from
a bg.

Yep, that's the normal case.

However I'm wondering if it's possible to get a bad eb which is cached.

Then we could hit such situation.

So I still believe being safe here still makes sense, especially who
knows future fuzzed image will be.

Plus one.
Personally, I'd rather like the version 1.

Thanks,
Su

Thanks,
Qu



Signed-off-by: Kangjie Lu <kjlu@xxxxxxx>
---
  fs/btrfs/extent-tree.c | 2 ++
  1 file changed, 2 insertions(+)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 994f0cc41799..b1e7985bcb9d 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -7303,6 +7303,8 @@ void btrfs_free_tree_block(struct btrfs_trans_handle *trans,
pin = 0;
  		cache = btrfs_lookup_block_group(fs_info, buf->start);
+		if (!cache)
+			goto out;
if (btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN)) {
  			pin_down_extent(fs_info, cache, buf->start,