Subject: Re: [syzbot] BUG: stack guard page was hit in inet6_release

From: John Fastabend <[email-masked]>
Date: Thu, 08 Dec 2022 01:07:36 -0800

Eric Dumazet wrote:
> On Wed, Dec 7, 2022 at 7:38 AM John Fastabend <[email-masked]> wrote:
> >
> > syzbot wrote:
> > > Hello,
> > >
> > > syzbot found the following issue on:
> > >
> > > HEAD commit:    6a30d3e3491d selftests: net: Use "grep -E" instead of "egr..
> > > git tree:       net
> > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=1576b11d880000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=cc4b2e0a8e8a8366
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=04c21ed96d861dccc5cd
> > > compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14e1656b880000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1077da23880000
> > >
> > > Downloadable assets:
> > > disk image: https://storage.googleapis.com/syzbot-assets/bbee3d5fc908/disk-6a30d3e3.raw.xz
> > > vmlinux: https://storage.googleapis.com/syzbot-assets/bf9e258de70e/vmlinux-6a30d3e3.xz
> > > kernel image: https://storage.googleapis.com/syzbot-assets/afaa6696b9e0/bzImage-6a30d3e3.xz
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > Reported-by: [email-masked]
> > >
> > > BUG: TASK stack guard page was hit at ffffc90003cd7fa8 (stack is ffffc90003cd8000..ffffc90003ce0000)
> > > stack guard page: 0000 [#1] PREEMPT SMP KASAN
> > > CPU: 0 PID: 3636 Comm: syz-executor238 Not tainted 6.1.0-rc7-syzkaller-00135-g6a30d3e3491d #0
> > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
> > > RIP: 0010:mark_lock.part.0+0x26/0x1910 kernel/locking/lockdep.c:4593
> > > Code: 00 00 00 00 41 57 41 56 41 55 41 89 d5 48 ba 00 00 00 00 00 fc ff df 41 54 49 89 f4 55 53 48 81 ec 38 01 00 00 48 8d 5c 24 38 <48> 89 3c 24 48 c7 44 24 38 b3 8a b5 41 48 c1 eb 03 48 c7 44 24 40
> > > RSP: 0018:ffffc90003cd7fb8 EFLAGS: 00010096
> > > RAX: 0000000000000004 RBX: ffffc90003cd7ff0 RCX: ffffffff8162a7bf
> > > RDX: dffffc0000000000 RSI: ffff88801f65e238 RDI: ffff88801f65d7c0
> > > RBP: ffff88801f65e25a R08: 0000000000000000 R09: ffffffff910f4aff
> > > R10: fffffbfff221e95f R11: 0000000000000000 R12: ffff88801f65e238
> > > R13: 0000000000000002 R14: 0000000000000000 R15: 0000000000040000
> > > FS:  0000000000000000(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
> > > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > CR2: ffffc90003cd7fa8 CR3: 000000000c28e000 CR4: 00000000003506f0
> > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > Call Trace:
> > >  <TASK>
> > >  mark_lock kernel/locking/lockdep.c:4598 [inline]
> > >  mark_usage kernel/locking/lockdep.c:4543 [inline]
> > >  __lock_acquire+0x847/0x56d0 kernel/locking/lockdep.c:5009
> > >  lock_acquire kernel/locking/lockdep.c:5668 [inline]
> > >  lock_acquire+0x1e3/0x630 kernel/locking/lockdep.c:5633
> > >  lock_sock_nested+0x3a/0xf0 net/core/sock.c:3447
> > >  lock_sock include/net/sock.h:1721 [inline]
> > >  sock_map_close+0x75/0x7b0 net/core/sock_map.c:1610
> >
> > I'll take a look likely something recent.
> 
> Fact that sock_map_close  can call itself seems risky.
> We might issue a one time warning and keep the host alive.

Agree seems better to check the condition than loop on close.
I still need to figure out the bug that got into this state
though. Thanks.

> 
> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> index 81beb16ab1ebfcb166f51f89a029fe1c28a629a4..a79771a6627b9b2f38ae6ce153ceff9e8c0be8d4
> 100644
> --- a/net/core/sock_map.c
> +++ b/net/core/sock_map.c
> @@ -1612,17 +1612,25 @@ void sock_map_close(struct sock *sk, long timeout)
>         psock = sk_psock_get(sk);
>         if (unlikely(!psock)) {
>                 rcu_read_unlock();
> +               saved_close = sk->sk_prot->close;
>                 release_sock(sk);
> -               return sk->sk_prot->close(sk, timeout);
> +       } else {
> +               saved_close = psock->saved_close;
> +               sock_map_remove_links(sk, psock);
> +               rcu_read_unlock();
> +               sk_psock_stop(psock);
> +               release_sock(sk);
> +               cancel_work_sync(&psock->work);
> +               sk_psock_put(sk, psock);
> +       }
> +       /* Make sure we do not recurse to us.
> +        * This is a bug, we can leak the socket instead
> +        * of crashing on a stack overflow.
> +        */
> +       if (saved_close == sock_map_close) {
> +               WARN_ON_ONCE(1);
> +               return;
>         }
> -
> -       saved_close = psock->saved_close;
> -       sock_map_remove_links(sk, psock);
> -       rcu_read_unlock();
> -       sk_psock_stop(psock);
> -       release_sock(sk);
> -       cancel_work_sync(&psock->work);
> -       sk_psock_put(sk, psock);
>         saved_close(sk, timeout);
>  }
>  EXPORT_SYMBOL_GPL(sock_map_close);