Messages in this thread | | | Subject | Re: [PATCH] btrfs: fix a NULL pointer dereference | From | Nikolay Borisov <> | Date | Thu, 14 Mar 2019 10:03:21 +0200 |
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On 14.03.19 г. 10:02 ч., 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.
Then I'd rather have ASSERT(cache)
> > 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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