netdev - Re: [PATCH net-next] mptcp: adjust to use netns refcount tracker

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Date:   Tue, 14 Dec 2021 09:57:34 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        syzbot <syzkaller@...glegroups.com>,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        Matthieu Baerts <matthieu.baerts@...sares.net>,
        Florian Westphal <fw@...len.de>
Subject: Re: [PATCH net-next] mptcp: adjust to use netns refcount tracker

On Mon, 2021-12-13 at 20:32 -0800, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> MPTCP can change sk_net_refcnt after sock_create_kern() call.
> 
> We need to change its corresponding get_net() to avoid
> a splat at release time, as in :
> 
> refcount_t: decrement hit 0; leaking memory.
> WARNING: CPU: 0 PID: 3599 at lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0 lib/refcount.c:31
> Modules linked in:
> CPU: 1 PID: 3599 Comm: syz-fuzzer Not tainted 5.16.0-rc4-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:refcount_warn_saturate+0xbf/0x1e0 lib/refcount.c:31
> Code: 1d b1 99 a1 09 31 ff 89 de e8 5d 3a 9c fd 84 db 75 e0 e8 74 36 9c fd 48 c7 c7 60 00 05 8a c6 05 91 99 a1 09 01 e8 cc 4b 27 05 <0f> 0b eb c4 e8 58 36 9c fd 0f b6 1d 80 99 a1 09 31 ff 89 de e8 28
> RSP: 0018:ffffc90001f5fab0 EFLAGS: 00010286
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: ffff888021873a00 RSI: ffffffff815f1e28 RDI: fffff520003ebf48
> RBP: 0000000000000004 R08: 0000000000000000 R09: 0000000000000000
> R10: ffffffff815ebbce R11: 0000000000000000 R12: 1ffff920003ebf5b
> R13: 00000000ffffffef R14: ffffffff8d2fcd94 R15: ffffc90001f5fd10
> FS:  000000c00008a090(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f0a5b59e300 CR3: 000000001cbe6000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  __refcount_dec include/linux/refcount.h:344 [inline]
>  refcount_dec include/linux/refcount.h:359 [inline]
>  ref_tracker_free+0x4fe/0x610 lib/ref_tracker.c:101
>  netns_tracker_free include/net/net_namespace.h:327 [inline]
>  put_net_track include/net/net_namespace.h:341 [inline]
>  __sk_destruct+0x4a6/0x920 net/core/sock.c:2042
>  sk_destruct+0xbd/0xe0 net/core/sock.c:2058
>  __sk_free+0xef/0x3d0 net/core/sock.c:2069
>  sk_free+0x78/0xa0 net/core/sock.c:2080
>  sock_put include/net/sock.h:1911 [inline]
>  __mptcp_close_ssk+0x435/0x590 net/mptcp/protocol.c:2276
>  __mptcp_destroy_sock+0x35f/0x830 net/mptcp/protocol.c:2702
>  mptcp_close+0x5f8/0x7f0 net/mptcp/protocol.c:2750
>  inet_release+0x12e/0x280 net/ipv4/af_inet.c:428
>  inet6_release+0x4c/0x70 net/ipv6/af_inet6.c:476
>  __sock_release+0xcd/0x280 net/socket.c:649
>  sock_close+0x18/0x20 net/socket.c:1314
>  __fput+0x286/0x9f0 fs/file_table.c:280
>  task_work_run+0xdd/0x1a0 kernel/task_work.c:164
>  tracehook_notify_resume include/linux/tracehook.h:189 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:175 [inline]
>  exit_to_user_mode_prepare+0x27e/0x290 kernel/entry/common.c:207
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
>  syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:300
>  do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> Fixes: ffa84b5ffb37 ("net: add netns refcount tracker to struct sock")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Cc: Mat Martineau <mathew.j.martineau@...ux.intel.com>
> Cc: Matthieu Baerts <matthieu.baerts@...sares.net>
> Cc: Florian Westphal <fw@...len.de>
> Cc: Paolo Abeni <pabeni@...hat.com>
> ---
>  net/mptcp/subflow.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
> index b8dd3441f7d00357dfac6121f6288b9300ea5201..24bc9d5e87be44542f5094cda39dcc59f8f9f10d 100644
> --- a/net/mptcp/subflow.c
> +++ b/net/mptcp/subflow.c
> @@ -1534,7 +1534,7 @@ int mptcp_subflow_create_socket(struct sock *sk, struct socket **new_sock)
>  	 * needs it.
>  	 */
>  	sf->sk->sk_net_refcnt = 1;
> -	get_net(net);
> +	get_net_track(net, &sf->sk->ns_tracker, GFP_KERNEL);
>  	sock_inuse_add(net, 1);
>  	err = tcp_set_ulp(sf->sk, "mptcp");
>  	release_sock(sf->sk);

LGTM, thanks Eric! 

(and more thanks for the whole tracking infra!)

Acked-by: Paolo Abeni <pabeni@...hat.com>