linux-kernel - [PATCH v3,bpf-next] bpf: Don't redirect packets with invalid pkt

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Date:   Fri, 15 Jul 2022 11:22:33 +0800
From:   Zhengchao Shao <shaozhengchao@...wei.com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <davem@...emloft.net>,
        <edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
        <hawk@...nel.org>
CC:     <ast@...nel.org>, <daniel@...earbox.net>, <andrii@...nel.org>,
        <martin.lau@...ux.dev>, <song@...nel.org>, <yhs@...com>,
        <john.fastabend@...il.com>, <kpsingh@...nel.org>, <sdf@...gle.com>,
        <bigeasy@...utronix.de>, <imagedong@...cent.com>,
        <petrm@...dia.com>, <arnd@...db.de>, <dsahern@...nel.org>,
        <talalahmad@...gle.com>, <keescook@...omium.org>,
        <haoluo@...gle.com>, <jolsa@...nel.org>, <weiyongjun1@...wei.com>,
        <yuehaibing@...wei.com>, <shaozhengchao@...wei.com>
Subject: [PATCH v3,bpf-next] 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: syzbot+7a12909485b94426aceb@...kaller.appspotmail.com
Signed-off-by: Zhengchao Shao <shaozhengchao@...wei.com>
---
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 | 11 +++++++++++
 net/bpf/test_run.c     |  3 +++
 net/core/dev.c         |  1 +
 3 files changed, 15 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index f6a27ab19202..8ea41ad0786b 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2459,6 +2459,17 @@ 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 (unlikely(!skb->len)) {
+		pr_err("%s\n", __func__);
+		skb_dump(KERN_ERR, skb, false);
+		WARN_ON_ONCE(1);
+	}
+#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