Messages in this thread | | | Date | Tue, 12 Jul 2022 09:58:39 -0700 | Subject | Re: [PATCH bpf-next] bpf: Don't redirect packets with invalid pkt_len | From | sdf@google ... |
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On 07/12, Zhengchao Shao 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 or others like bpf_prog_test 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@syzkaller.appspotmail.com > Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com> > --- > net/core/filter.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-)
> diff --git a/net/core/filter.c b/net/core/filter.c > index 4ef77ec5255e..27801b314960 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -2122,6 +2122,11 @@ static int __bpf_redirect_no_mac(struct sk_buff > *skb, struct net_device *dev, > { > unsigned int mlen = skb_network_offset(skb);
> + if (unlikely(skb->len == 0)) { > + kfree_skb(skb); > + return -EINVAL; > + } > + > if (mlen) { > __skb_pull(skb, mlen);
> @@ -2143,7 +2148,9 @@ static int __bpf_redirect_common(struct sk_buff > *skb, struct net_device *dev, > u32 flags) > { > /* Verify that a link layer header is carried */ > - if (unlikely(skb->mac_header >= skb->network_header)) { > + if (unlikely(skb->mac_header >= skb->network_header) || > + (min_t(u32, skb_mac_header_len(skb), skb->len) < > + (u32)dev->min_header_len)) {
Why check skb->len != 0 above but skb->len < dev->min_header_len here? I guess it doesn't make sense in __bpf_redirect_no_mac because we know that mac is empty, but why do we care in __bpf_redirect_common? Why not put this check in the common __bpf_redirect?
Also, it's still not clear to me whether we should bake it into the core stack vs having some special checks from test_prog_run only. I'm assuming the issue is that we can construct illegal skbs with that test_prog_run interface, so maybe start by fixing that?
Did you have a chance to look at the reproducer more closely? What exactly is it doing?
> kfree_skb(skb); > return -ERANGE; > } > -- > 2.17.1
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