On Fri, Jul 15, 2022 at 4:51 AM 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 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@xxxxxxxxxxxxxxxxxxxxxxxxx > Signed-off-by: Zhengchao Shao <shaozhengchao@xxxxxxxxxx> Reviewed-by: Stanislav Fomichev <sdf@xxxxxxxxxx> Looks like it addresses everything? > --- > v3: modify debug print > v2: need move checking to convert___skb_to_skb and add debug info > v1: should not check len in fast path > > include/linux/skbuff.h | 8 ++++++++ > net/bpf/test_run.c | 3 +++ > net/core/dev.c | 1 + > 3 files changed, 12 insertions(+) > > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h > index f6a27ab19202..82e8368ba6e6 100644 > --- a/include/linux/skbuff.h > +++ b/include/linux/skbuff.h > @@ -2459,6 +2459,14 @@ static inline void skb_set_tail_pointer(struct sk_buff *skb, const int offset) > > #endif /* NET_SKBUFF_DATA_USES_OFFSET */ > > +static inline void skb_assert_len(struct sk_buff *skb) > +{ > +#ifdef CONFIG_DEBUG_NET > + if (WARN_ONCE(!skb->len, "%s\n", __func__)) > + DO_ONCE_LITE(skb_dump, KERN_ERR, skb, false); > +#endif /* CONFIG_DEBUG_NET */ > +} > + > /* > * Add data to an sk_buff > */ > diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c > index 2ca96acbc50a..dc9dc0bedca0 100644 > --- a/net/bpf/test_run.c > +++ b/net/bpf/test_run.c > @@ -955,6 +955,9 @@ static int convert___skb_to_skb(struct sk_buff *skb, struct __sk_buff *__skb) > { > struct qdisc_skb_cb *cb = (struct qdisc_skb_cb *)skb->cb; > > + if (!skb->len) > + return -EINVAL; > + > if (!__skb) > return 0; > > diff --git a/net/core/dev.c b/net/core/dev.c > index d588fd0a54ce..716df64fcfa5 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -4168,6 +4168,7 @@ int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev) > bool again = false; > > skb_reset_mac_header(skb); > + skb_assert_len(skb); > > if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_SCHED_TSTAMP)) > __skb_tstamp_tx(skb, NULL, NULL, skb->sk, SCM_TSTAMP_SCHED); > -- > 2.17.1 >
