[PATCH v1 net] net: Remove WARN_ON_ONCE(sk->sk_forward_alloc) from sk_stream_kill_queues().

[PATCH v1 net] net: Remove WARN_ON_ONCE(sk->sk_forward_alloc) from sk_stream_kill_queues().

[Kuniyuki Iwashima]

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.  The skb
has not been uncharged in inet_csk_destroy_sock(), thus, calling
sk_stream_kill_queues() there triggers the WARN_ON_ONCE().

The same check has been in inet_sock_destruct() from at least
v2.6.  Since only CAIF is not calling inet_sock_destruct() among
the users of sk_stream_kill_queues(), we remove the WARN_ON_ONCE()
from sk_stream_kill_queues() and add it to caif_sock_destructor().

[0]: https://lore.kernel.org/netdev/39725AB4-88F1-41B3-B07F-949C5CAEFF4F@icloud.com/
[1]: https://github.com/multipath-tcp/mptcp_net-next/issues/341
[2]:
WARNING: CPU: 0 PID: 3232 at net/core/stream.c:212 sk_stream_kill_queues+0x2f9/0x3e0
Modules linked in:
CPU: 0 PID: 3232 Comm: syz-executor.0 Not tainted 6.2.0-rc5ab24eb4698afbe147b424149c529e2a43ec24eb5 #2
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
RIP: 0010:sk_stream_kill_queues+0x2f9/0x3e0
Code: 03 0f b6 04 02 84 c0 74 08 3c 03 0f 8e ec 00 00 00 8b ab 08 01 00 00 e9 60 ff ff ff e8 d0 5f b6 fe 0f 0b eb 97 e8 c7 5f b6 fe <0f> 0b eb a0 e8 be 5f b6 fe 0f 0b e9 6a fe ff ff e8 02 07 e3 fe e9
RSP: 0018:ffff88810570fc68 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff888101f38f40 RSI: ffffffff8285e529 RDI: 0000000000000005
RBP: 0000000000000ce0 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000ce0 R11: 0000000000000001 R12: ffff8881009e9488
R13: ffffffff84af2cc0 R14: 0000000000000000 R15: ffff8881009e9458
FS:  00007f7fdfbd5800(0000) GS:ffff88811b600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b32923000 CR3: 00000001062fc006 CR4: 0000000000170ef0
Call Trace:
 <TASK>
 inet_csk_destroy_sock+0x1a1/0x320
 __tcp_close+0xab6/0xe90
 tcp_close+0x30/0xc0
 inet_release+0xe9/0x1f0
 inet6_release+0x4c/0x70
 __sock_release+0xd2/0x280
 sock_close+0x15/0x20
 __fput+0x252/0xa20
 task_work_run+0x169/0x250
 exit_to_user_mode_prepare+0x113/0x120
 syscall_exit_to_user_mode+0x1d/0x40
 do_syscall_64+0x48/0x90
 entry_SYSCALL_64_after_hwframe+0x72/0xdc
RIP: 0033:0x7f7fdf7ae28d
Code: c1 20 00 00 75 10 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 ee fb ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 37 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00000000007dfbb0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 00007f7fdf7ae28d
RDX: 0000000000000000 RSI: ffffffffffffffff RDI: 0000000000000003
RBP: 0000000000000000 R08: 000000007f338e0f R09: 0000000000000e0f
R10: 000000007f338e13 R11: 0000000000000293 R12: 00007f7fdefff000
R13: 00007f7fdefffcd8 R14: 00007f7fdefffce0 R15: 00007f7fdefffcd8
 </TASK>

Fixes: b5fc29233d28 ("inet6: Remove inet6_destroy_sock() in sk->sk_prot->destroy().")
Reported-by: syzbot <syzkaller@googlegroups.com>
Reported-by: Christoph Paasch <christophpaasch@icloud.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 net/caif/caif_socket.c | 1 +
 net/core/stream.c      | 1 -
 2 files changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/caif/caif_socket.c b/net/caif/caif_socket.c
index 748be7253248..78c9729a6057 100644
--- a/net/caif/caif_socket.c
+++ b/net/caif/caif_socket.c
@@ -1015,6 +1015,7 @@ static void caif_sock_destructor(struct sock *sk)
 		return;
 	}
 	sk_stream_kill_queues(&cf_sk->sk);
+	WARN_ON_ONCE(sk->sk_forward_alloc);
 	caif_free_client(&cf_sk->layer);
 }
 
diff --git a/net/core/stream.c b/net/core/stream.c
index cd06750dd329..434446ab14c5 100644
--- a/net/core/stream.c
+++ b/net/core/stream.c
@@ -209,7 +209,6 @@ void sk_stream_kill_queues(struct sock *sk)
 	sk_mem_reclaim_final(sk);
 
 	WARN_ON_ONCE(sk->sk_wmem_queued);
-	WARN_ON_ONCE(sk->sk_forward_alloc);
 
 	/* It is _impossible_ for the backlog to contain anything
 	 * when we get here.  All user references to this socket
-- 
2.30.2

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

[Eric Dumazet]

On Tue, Feb 7, 2023 at 7:37 PM Kuniyuki Iwashima <kuniyu@amazon.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 ?

 The skb
> has not been uncharged in inet_csk_destroy_sock(), thus, calling
> sk_stream_kill_queues() there triggers the WARN_ON_ONCE().
>
> The same check has been in inet_sock_destruct() from at least
> v2.6.  Since only CAIF is not calling inet_sock_destruct() among
> the users of sk_stream_kill_queues(), we remove the WARN_ON_ONCE()
> from sk_stream_kill_queues() and add it to caif_sock_destructor().
>
> [0]: https://lore.kernel.org/netdev/39725AB4-88F1-41B3-B07F-949C5CAEFF4F@icloud.com/
> [1]: https://github.com/multipath-tcp/mptcp_net-next/issues/341
> [2]:
> WARNING: CPU: 0 PID: 3232 at net/core/stream.c:212 sk_stream_kill_queues+0x2f9/0x3e0
> Modules linked in:
> CPU: 0 PID: 3232 Comm: syz-executor.0 Not tainted 6.2.0-rc5ab24eb4698afbe147b424149c529e2a43ec24eb5 #2
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
> RIP: 0010:sk_stream_kill_queues+0x2f9/0x3e0
> Code: 03 0f b6 04 02 84 c0 74 08 3c 03 0f 8e ec 00 00 00 8b ab 08 01 00 00 e9 60 ff ff ff e8 d0 5f b6 fe 0f 0b eb 97 e8 c7 5f b6 fe <0f> 0b eb a0 e8 be 5f b6 fe 0f 0b e9 6a fe ff ff e8 02 07 e3 fe e9
> RSP: 0018:ffff88810570fc68 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: ffff888101f38f40 RSI: ffffffff8285e529 RDI: 0000000000000005
> RBP: 0000000000000ce0 R08: 0000000000000005 R09: 0000000000000000
> R10: 0000000000000ce0 R11: 0000000000000001 R12: ffff8881009e9488
> R13: ffffffff84af2cc0 R14: 0000000000000000 R15: ffff8881009e9458
> FS:  00007f7fdfbd5800(0000) GS:ffff88811b600000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000001b32923000 CR3: 00000001062fc006 CR4: 0000000000170ef0
> Call Trace:
>  <TASK>
>  inet_csk_destroy_sock+0x1a1/0x320
>  __tcp_close+0xab6/0xe90
>  tcp_close+0x30/0xc0
>  inet_release+0xe9/0x1f0
>  inet6_release+0x4c/0x70
>  __sock_release+0xd2/0x280
>  sock_close+0x15/0x20
>  __fput+0x252/0xa20
>  task_work_run+0x169/0x250
>  exit_to_user_mode_prepare+0x113/0x120
>  syscall_exit_to_user_mode+0x1d/0x40
>  do_syscall_64+0x48/0x90
>  entry_SYSCALL_64_after_hwframe+0x72/0xdc
> RIP: 0033:0x7f7fdf7ae28d
> Code: c1 20 00 00 75 10 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 ee fb ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 37 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
> RSP: 002b:00000000007dfbb0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
> RAX: 0000000000000000 RBX: 0000000000000004 RCX: 00007f7fdf7ae28d
> RDX: 0000000000000000 RSI: ffffffffffffffff RDI: 0000000000000003
> RBP: 0000000000000000 R08: 000000007f338e0f R09: 0000000000000e0f
> R10: 000000007f338e13 R11: 0000000000000293 R12: 00007f7fdefff000
> R13: 00007f7fdefffcd8 R14: 00007f7fdefffce0 R15: 00007f7fdefffcd8
>  </TASK>
>
> Fixes: b5fc29233d28 ("inet6: Remove inet6_destroy_sock() in sk->sk_prot->destroy().")
> Reported-by: syzbot <syzkaller@googlegroups.com>
> Reported-by: Christoph Paasch <christophpaasch@icloud.com>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> ---
>  net/caif/caif_socket.c | 1 +
>  net/core/stream.c      | 1 -
>  2 files changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/caif/caif_socket.c b/net/caif/caif_socket.c
> index 748be7253248..78c9729a6057 100644
> --- a/net/caif/caif_socket.c
> +++ b/net/caif/caif_socket.c
> @@ -1015,6 +1015,7 @@ static void caif_sock_destructor(struct sock *sk)
>                 return;
>         }
>         sk_stream_kill_queues(&cf_sk->sk);
> +       WARN_ON_ONCE(sk->sk_forward_alloc);
>         caif_free_client(&cf_sk->layer);
>  }
>
> diff --git a/net/core/stream.c b/net/core/stream.c
> index cd06750dd329..434446ab14c5 100644
> --- a/net/core/stream.c
> +++ b/net/core/stream.c
> @@ -209,7 +209,6 @@ void sk_stream_kill_queues(struct sock *sk)
>         sk_mem_reclaim_final(sk);
>
>         WARN_ON_ONCE(sk->sk_wmem_queued);
> -       WARN_ON_ONCE(sk->sk_forward_alloc);
>
>         /* It is _impossible_ for the backlog to contain anything
>          * when we get here.  All user references to this socket
> --
> 2.30.2
>

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

[Kuniyuki Iwashima]

From:   Eric Dumazet <edumazet@google.com>
Date:   Tue, 7 Feb 2023 20:25:19 +0100
> On Tue, Feb 7, 2023 at 7:37 PM Kuniyuki Iwashima <kuniyu@amazon.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 ?

Christoph attached a repro on GitHub [0], but I couldn't reproduce it,
so I also thought the WARN_ON_ONCE() was triggered by a negative value.

[0]: https://github.com/multipath-tcp/mptcp_net-next/issues/341#issuecomment-1410818557


> 
>  The skb
> > has not been uncharged in inet_csk_destroy_sock(), thus, calling
> > sk_stream_kill_queues() there triggers the WARN_ON_ONCE().
> >
> > The same check has been in inet_sock_destruct() from at least
> > v2.6.  Since only CAIF is not calling inet_sock_destruct() among
> > the users of sk_stream_kill_queues(), we remove the WARN_ON_ONCE()
> > from sk_stream_kill_queues() and add it to caif_sock_destructor().
> >
> > [0]: https://lore.kernel.org/netdev/39725AB4-88F1-41B3-B07F-949C5CAEFF4F@icloud.com/
> > [1]: https://github.com/multipath-tcp/mptcp_net-next/issues/341
> > [2]:
> > WARNING: CPU: 0 PID: 3232 at net/core/stream.c:212 sk_stream_kill_queues+0x2f9/0x3e0
> > Modules linked in:
> > CPU: 0 PID: 3232 Comm: syz-executor.0 Not tainted 6.2.0-rc5ab24eb4698afbe147b424149c529e2a43ec24eb5 #2
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
> > RIP: 0010:sk_stream_kill_queues+0x2f9/0x3e0
> > Code: 03 0f b6 04 02 84 c0 74 08 3c 03 0f 8e ec 00 00 00 8b ab 08 01 00 00 e9 60 ff ff ff e8 d0 5f b6 fe 0f 0b eb 97 e8 c7 5f b6 fe <0f> 0b eb a0 e8 be 5f b6 fe 0f 0b e9 6a fe ff ff e8 02 07 e3 fe e9
> > RSP: 0018:ffff88810570fc68 EFLAGS: 00010293
> > RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> > RDX: ffff888101f38f40 RSI: ffffffff8285e529 RDI: 0000000000000005
> > RBP: 0000000000000ce0 R08: 0000000000000005 R09: 0000000000000000
> > R10: 0000000000000ce0 R11: 0000000000000001 R12: ffff8881009e9488
> > R13: ffffffff84af2cc0 R14: 0000000000000000 R15: ffff8881009e9458
> > FS:  00007f7fdfbd5800(0000) GS:ffff88811b600000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000001b32923000 CR3: 00000001062fc006 CR4: 0000000000170ef0
> > Call Trace:
> >  <TASK>
> >  inet_csk_destroy_sock+0x1a1/0x320
> >  __tcp_close+0xab6/0xe90
> >  tcp_close+0x30/0xc0
> >  inet_release+0xe9/0x1f0
> >  inet6_release+0x4c/0x70
> >  __sock_release+0xd2/0x280
> >  sock_close+0x15/0x20
> >  __fput+0x252/0xa20
> >  task_work_run+0x169/0x250
> >  exit_to_user_mode_prepare+0x113/0x120
> >  syscall_exit_to_user_mode+0x1d/0x40
> >  do_syscall_64+0x48/0x90
> >  entry_SYSCALL_64_after_hwframe+0x72/0xdc
> > RIP: 0033:0x7f7fdf7ae28d
> > Code: c1 20 00 00 75 10 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 ee fb ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 37 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
> > RSP: 002b:00000000007dfbb0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
> > RAX: 0000000000000000 RBX: 0000000000000004 RCX: 00007f7fdf7ae28d
> > RDX: 0000000000000000 RSI: ffffffffffffffff RDI: 0000000000000003
> > RBP: 0000000000000000 R08: 000000007f338e0f R09: 0000000000000e0f
> > R10: 000000007f338e13 R11: 0000000000000293 R12: 00007f7fdefff000
> > R13: 00007f7fdefffcd8 R14: 00007f7fdefffce0 R15: 00007f7fdefffcd8
> >  </TASK>
> >
> > Fixes: b5fc29233d28 ("inet6: Remove inet6_destroy_sock() in sk->sk_prot->destroy().")
> > Reported-by: syzbot <syzkaller@googlegroups.com>
> > Reported-by: Christoph Paasch <christophpaasch@icloud.com>
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> > ---
> >  net/caif/caif_socket.c | 1 +
> >  net/core/stream.c      | 1 -
> >  2 files changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/caif/caif_socket.c b/net/caif/caif_socket.c
> > index 748be7253248..78c9729a6057 100644
> > --- a/net/caif/caif_socket.c
> > +++ b/net/caif/caif_socket.c
> > @@ -1015,6 +1015,7 @@ static void caif_sock_destructor(struct sock *sk)
> >                 return;
> >         }
> >         sk_stream_kill_queues(&cf_sk->sk);
> > +       WARN_ON_ONCE(sk->sk_forward_alloc);
> >         caif_free_client(&cf_sk->layer);
> >  }
> >
> > diff --git a/net/core/stream.c b/net/core/stream.c
> > index cd06750dd329..434446ab14c5 100644
> > --- a/net/core/stream.c
> > +++ b/net/core/stream.c
> > @@ -209,7 +209,6 @@ void sk_stream_kill_queues(struct sock *sk)
> >         sk_mem_reclaim_final(sk);
> >
> >         WARN_ON_ONCE(sk->sk_wmem_queued);
> > -       WARN_ON_ONCE(sk->sk_forward_alloc);
> >
> >         /* It is _impossible_ for the backlog to contain anything
> >          * when we get here.  All user references to this socket
> > --
> > 2.30.2
> >

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

[Kuniyuki Iwashima]

From:   Eric Dumazet <edumazet@google.com>
Date:   Tue, 7 Feb 2023 20:25:19 +0100
> On Tue, Feb 7, 2023 at 7:37 PM Kuniyuki Iwashima <kuniyu@amazon.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<---

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

[Kuniyuki Iwashima]

From:   Kuniyuki Iwashima <kuniyu@amazon.com>
Date:   Tue, 7 Feb 2023 16:37:13 -0800
> From:   Eric Dumazet <edumazet@google.com>
> Date:   Tue, 7 Feb 2023 20:25:19 +0100
> > On Tue, Feb 7, 2023 at 7:37 PM Kuniyuki Iwashima <kuniyu@amazon.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<---

Sorry, I missed unistd.h here while copy-and-paste.

#include <unistd.h>
> #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<---

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

[Kuniyuki Iwashima]

From:   Kuniyuki Iwashima <kuniyu@amazon.com>
Date:   Tue, 7 Feb 2023 16:37:13 -0800
> From:   Eric Dumazet <edumazet@google.com>
> Date:   Tue, 7 Feb 2023 20:25:19 +0100
> > On Tue, Feb 7, 2023 at 7:37 PM Kuniyuki Iwashima <kuniyu@amazon.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.

This was just before sk_stream_kill_queues(), and actually
sk->sk_forward_alloc was able to be negative by the
skb_set_owner_r() as you thought.

I'll fix this, thank you!