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From:   Eric Dumazet <edumazet@google.com>
Date:   Wed, 7 Dec 2022 09:12:59 +0100
Message-ID: <CANn89iK2UN1FmdUcH12fv_xiZkv2G+Nskvmq7fG6aA_6VKRf6g@mail.gmail.com>
Subject: Re: [syzbot] BUG: stack guard page was hit in inet6_release
To:     John Fastabend <john.fastabend@gmail.com>
Cc:     syzbot <syzbot+04c21ed96d861dccc5cd@syzkaller.appspotmail.com>,
        bpf@vger.kernel.org, davem@davemloft.net, jakub@cloudflare.com,
        kuba@kernel.org, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, pabeni@redhat.com,
        syzkaller-bugs@googlegroups.com
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On Wed, Dec 7, 2022 at 7:38 AM John Fastabend <john.fastabend@gmail.com> 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: syzbot+04c21ed96d861dccc5cd@syzkaller.appspotmail.com
> >
> > 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.

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);