From: Zhengchao Shao <shaozhengchao@xxxxxxxxxx> commit fd1894224407c484f652ad456e1ce423e89bb3eb upstream. 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> Link: https://lore.kernel.org/r/20220715115559.139691-1-shaozhengchao@xxxxxxxxxx Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- include/linux/skbuff.h | 8 ++++++++ net/bpf/test_run.c | 3 +++ net/core/dev.c | 1 + 3 files changed, 12 insertions(+) --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -2201,6 +2201,14 @@ static inline void skb_set_tail_pointer( #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 */ --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -200,6 +200,9 @@ static int convert___skb_to_skb(struct s { struct qdisc_skb_cb *cb = (struct qdisc_skb_cb *)skb->cb; + if (!skb->len) + return -EINVAL; + if (!__skb) return 0; --- a/net/core/dev.c +++ b/net/core/dev.c @@ -3712,6 +3712,7 @@ static int __dev_queue_xmit(struct sk_bu 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, skb->sk, SCM_TSTAMP_SCHED);
