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

[Kuniyuki Iwashima <kuniyu@amazon.com>]

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
> >