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SubjectRe: [PATCH] btrfs: fix a NULL pointer dereference
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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.

Thanks,
Qu

>
>>
>> Signed-off-by: Kangjie Lu <kjlu@umn.edu>
>> ---
>> 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,
>>

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