Re: [PATCH] btrfs: qgroup: fix slab-out-of-bounds in btrfs_qgroup_inherit

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2024/6/24 12:37, Jeongjun Park 写道:
> If a value exists in inherit->num_ref_copies or inherit->num_excl_copies,
> an out-of-bounds vulnerability occurs.
>

Thanks for the fix.

Although I'm still not 100% sure what's going wrong.

The original report
(https://lore.kernel.org/lkml/000000000000bc19ba061a67ca77@google.com/T/)
is showing a backtrace when creating snapshot.

In that case they should all go through __btrfs_ioctl_snap_create(), and
since it has qgroup_inherit, it can only come from
btrfs_ioctl_snap_create_v2().

But in that function, we have just called btrfs_qgroup_check_inherit()
function and it already has the check on num_ref_copies/num_excl_copies.

So in that case it should not even happen.

I think the root cause is why the existing btrfs_qgroup_check_inherit()
doesn't catch the problem in the first place.

Thanks,
Qu

> Therefore, you need to add code to check the presence or absence of
> that value.
>
> Regards.
> Jeongjun Park.
>
> Reported-by: syzbot+a0d1f7e26910be4dc171@syzkaller.appspotmail.com
> Fixes: 3f5e2d3b3877 ("Btrfs: fix missing check in the btrfs_qgroup_inherit()")
> Signed-off-by: Jeongjun Park <aha310510@gmail.com>
> ---
>   fs/btrfs/qgroup.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/fs/btrfs/qgroup.c b /fs/btrfs/qgroup.c
> index fc2a7ea26354..23beac746637 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -3270,6 +3270,10 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
>   	}
>
>   	if (inherit) {
> +		if (inherit->num_ref_copies > 0 || inherit->num_excl_copies > 0) {
> +			ret = -EINVAL;
> +			goto out;
> +		}
>   		i_qgroups = (u64 *)(inherit + 1);
>   		nums = inherit->num_qgroups + 2 * inherit->num_ref_copies +
>   		       2 * inherit->num_excl_copies;
> --
>