User can use AF_PACKET socket to send packets with the length of 0.
When min_header_len equals to 0, packet_snd will call __dev_queue_xmit
to send packets, and sock->type can be any type.

Reported-by: syzbot+5ea725c25d06fb9114c4@syzkaller.appspotmail.com
Fixes: fd1894224407 ("bpf: Don't redirect packets with invalid pkt_len")
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
---
 net/packet/af_packet.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index d08c4728523b..5cbe07116e04 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3037,8 +3037,8 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
 	if (err)
 		goto out_free;
 
-	if (sock->type == SOCK_RAW &&
-	    !dev_validate_header(dev, skb->data, len)) {
+	if ((sock->type == SOCK_RAW &&
+	     !dev_validate_header(dev, skb->data, len)) || !skb->len) {
 		err = -EINVAL;
 		goto out_free;
 	}
-- 
2.17.1

Hello:

This patch was applied to netdev/net-next.git (master)
by David S. Miller <davem@davemloft.net>:

On Wed, 27 Jul 2022 17:33:12 +0800 you wrote:
> User can use AF_PACKET socket to send packets with the length of 0.
> When min_header_len equals to 0, packet_snd will call __dev_queue_xmit
> to send packets, and sock->type can be any type.
> 
> Reported-by: syzbot+5ea725c25d06fb9114c4@syzkaller.appspotmail.com
> Fixes: fd1894224407 ("bpf: Don't redirect packets with invalid pkt_len")
> Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
> 
> [...]

Here is the summary with links:
  - [net-next] net/af_packet: check len when min_header_len equals to 0
    https://git.kernel.org/netdev/net-next/c/dc633700f00f

You are awesome, thank you!
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