On Wed, Jul 13, 2022 at 11:05 PM Zhengchao Shao <shaozhengchao@xxxxxxxxxx> wrote: > > Syzbot found an issue [1]: fq_codel_drop() try to drop a flow whitout any > skbs, that is, the flow->head is null. > The root cause, as the [2] says, is because that bpf_prog_test_run_skb() > run a bpf prog which redirects empty skbs. > So we should determine whether the length of the packet modified by bpf > prog is valid before forwarding it directly. > > LINK: [1] https://syzkaller.appspot.com/bug?id=0b84da80c2917757915afa89f7738a9d16ec96c5 > LINK: [2] https://www.spinics.net/lists/netdev/msg777503.html > > Reported-by: syzbot+7a12909485b94426aceb@xxxxxxxxxxxxxxxxxxxxxxxxx > Signed-off-by: Zhengchao Shao <shaozhengchao@xxxxxxxxxx> Reviewed-by: Stanislav Fomichev <sdf@xxxxxxxxxx> Daniel, do you see any issues with this approach? I wonder if we might also want to add some WARN_ON to the __bpf_redirect_common routine gated by #ifdef CONFIG_DEBUG_NET ? In case syscaller manages to hit similar issues elsewhere.. > --- > v1: should not check len in fast path > > net/bpf/test_run.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c > index 2ca96acbc50a..750d7d173a20 100644 > --- a/net/bpf/test_run.c > +++ b/net/bpf/test_run.c > @@ -1152,6 +1152,12 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr, > ret = convert___skb_to_skb(skb, ctx); > if (ret) > goto out; > + > + if (skb->len == 0) { > + ret = -EINVAL; > + goto out; > + } > + > ret = bpf_test_run(prog, skb, repeat, &retval, &duration, false); > if (ret) > goto out; > -- > 2.17.1 >
