Commit fd189422 authored by Zhengchao Shao's avatar Zhengchao Shao Committed by Alexei Starovoitov
Browse files

bpf: Don't redirect packets with invalid pkt_len 

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: default avatar <syzbot+7a12909485b94426aceb@syzkaller.appspotmail.com>
Signed-off-by: default avatarZhengchao Shao <shaozhengchao@huawei.com>
Reviewed-by: default avatarStanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20220715115559.139691-1-shaozhengchao@huawei.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 92f61973

include/linux/skbuff.h

+8 −0
Original line number Diff line number Diff line
@@ -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

 */

net/bpf/test_run.c

+3 −0
Original line number Diff line number Diff line
@@ -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;

net/core/dev.c

+1 −0
Original line number Diff line number Diff line
@@ -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);