Messages in this thread | | | Subject | Re: [PATCH] btrfs: fix a NULL pointer dereference | From | Qu Wenruo <> | Date | Thu, 14 Mar 2019 16:02:02 +0800 |
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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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