Re: [syzbot] [bcachefs?] KASAN: slab-use-after-free Read in bch2_reconstruct_alloc

[Qu Wenruo]

在 2024/10/25 15:08, Lizhi Xu 写道:
> On Fri, 25 Oct 2024 14:49:48 +1030, Qu Wenruo wrote:
> > > use the input logical can't find the extent root, so add sanity check for
> > > extent root before search slot.
> > >
> > > #syz test
> > >
> > > diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
> > > index f8e1d5b2c512..87eaf5dd2d5d 100644
> > > --- a/fs/btrfs/backref.c
> > > +++ b/fs/btrfs/backref.c
> > > @@ -2213,6 +2213,9 @@ int extent_from_logical(struct btrfs_fs_info *fs_info, u64 logical,
> > >        key.objectid = logical;
> > >        key.offset = (u64)-1;
> > >
> > > +     if (!extent_root)
> > > +             return -ENOENT;
> >
> > Considering we have a lot of such btrfs_search_slot() without checking
> > if the csum/extent root is NULL, can we move the check into
> > btrfs_search_slot()?
> Yes, judging in btrfs_search_slot can fix the current issue while also
> avoiding similar problems.

Can't wait for your formal fix on this.

Thanks,
Qu

> #syz test
>
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index 0cc919d15b14..9c05cab473f5 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -2010,7 +2010,7 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>   		      const struct btrfs_key *key, struct btrfs_path *p,
>   		      int ins_len, int cow)
>   {
> -	struct btrfs_fs_info *fs_info = root->fs_info;
> +	struct btrfs_fs_info *fs_info;
>   	struct extent_buffer *b;
>   	int slot;
>   	int ret;
> @@ -2023,6 +2023,10 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>   	int min_write_lock_level;
>   	int prev_cmp;
>
> +	if (!root)
> +		return -EINVAL;
> +
> +	fs_info = root->fs_info;
>   	might_sleep();
>
>   	lowest_level = p->lowest_level;