netdev - Re: [PATCH v1 net] net: Remove WARN_ON_ONCE(sk->sk_forward_alloc) from sk_stream_kill

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Date:   Tue, 7 Feb 2023 16:37:13 -0800
From:   Kuniyuki Iwashima <kuniyu@...zon.com>
To:     <edumazet@...gle.com>
CC:     <christophpaasch@...oud.com>, <davem@...emloft.net>,
        <kuba@...nel.org>, <kuni1840@...il.com>, <kuniyu@...zon.com>,
        <matthieu.baerts@...sares.net>, <netdev@...r.kernel.org>,
        <pabeni@...hat.com>, <syzkaller@...glegroups.com>
Subject: Re: [PATCH v1 net] net: Remove WARN_ON_ONCE(sk->sk_forward_alloc) from sk_stream_kill_queues().

From:   Eric Dumazet <edumazet@...gle.com>
Date:   Tue, 7 Feb 2023 20:25:19 +0100
> On Tue, Feb 7, 2023 at 7:37 PM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> >
> > In commit b5fc29233d28 ("inet6: Remove inet6_destroy_sock() in
> > sk->sk_prot->destroy()."), we delay freeing some IPv6 resources
> > from sk->destroy() to sk->sk_destruct().
> >
> > Christoph Paasch reported the commit started triggering
> > WARN_ON_ONCE(sk->sk_forward_alloc) in sk_stream_kill_queues()
> > (See [0 - 2]).
> >
> > For example, if inet6_sk(sk)->rxopt is not zero by setting
> > IPV6_RECVPKTINFO or its friends, tcp_v6_do_rcv() clones a skb
> > and calls skb_set_owner_r(), which charges it to sk.
> 
> skb_set_owner_r() in this place seems wrong.
> This could lead to a negative sk->sk_forward_alloc
> (because we have not sk_rmem_schedule() it ?)
> 
> Do you have a repro ?

I created a repro and confirmed sk->sk_forward_alloc was always positive.

---8<---
#include <stdio.h>

#include <sys/socket.h>
#include <netinet/in.h>

#define IPV6_FLOWINFO		11

int main(void)
{
	struct sockaddr_in6 addr = {
		.sin6_family = AF_INET6,
		.sin6_addr = in6addr_any,
		.sin6_port = htons(0),
	};
	int fd, ret = 0;
	socklen_t len;

	ret = socket(AF_INET6, SOCK_STREAM, IPPROTO_IP);
	perror("socket");
	if (ret < 0)
		return ret;

	fd = ret;
	ret = setsockopt(fd, SOL_IPV6, IPV6_FLOWINFO, &(int){1}, sizeof(int));
	perror("setsockopt");

	ret = bind(fd, (struct sockaddr *)&addr, sizeof(addr));
	perror("bind");
	if (ret)
		goto out;

	len = sizeof(addr);
	ret = getsockname(fd, (struct sockaddr *)&addr, &len);
	perror("getsockname");
	if (ret)
		goto out;

	ret = connect(fd, (struct sockaddr *)&addr, len);
	perror("connect");
	if (ret)
		goto out;

out:
	close(fd);

	return ret;
}
---8<---