netdev - Re: [PATCH net] mptcp: fix NULL ptr dereference in inet_csk

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Date:   Fri, 10 Dec 2021 19:32:43 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     mptcp@...ts.linux.dev, Geliang Tang <geliangtang@...il.com>
Subject: Re: [PATCH net] mptcp: fix NULL ptr dereference in inet_csk_accept()

On Fri, 2021-12-10 at 17:51 +0100, Paolo Abeni wrote:
> Since commit 740d798e8767 ("mptcp: remove id 0 address"), the PM
> can remove the MPTCP first subflow in response to the netlink DEL_ADDR
> command. At subflow removal time, the TCP subflow socket is orphaned.
> 
> If the relevant MPTCP socket is in listening status and such
> operation races with an accept(), the kernel will access a NULL wait
> queue, as reported by syzbot:
> 
> general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
> CPU: 1 PID: 6550 Comm: syz-executor122 Not tainted 5.16.0-rc4-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:__lock_acquire+0xd7d/0x54a0 kernel/locking/lockdep.c:4897
> Code: 0f 0e 41 be 01 00 00 00 0f 86 c8 00 00 00 89 05 69 cc 0f 0e e9 bd 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 da 48 c1 ea 03 <80> 3c 02 00 0f 85 f3 2f 00 00 48 81 3b 20 75 17 8f 0f 84 52 f3 ff
> RSP: 0018:ffffc90001f2f818 EFLAGS: 00010016
> RAX: dffffc0000000000 RBX: 0000000000000018 RCX: 0000000000000000
> RDX: 0000000000000003 RSI: 0000000000000000 RDI: 0000000000000001
> RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000001
> R10: 0000000000000000 R11: 000000000000000a R12: 0000000000000000
> R13: ffff88801b98d700 R14: 0000000000000000 R15: 0000000000000001
> FS:  00007f177cd3d700(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f177cd1b268 CR3: 000000001dd55000 CR4: 0000000000350ee0
> Call Trace:
>  <TASK>
>  lock_acquire kernel/locking/lockdep.c:5637 [inline]
>  lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5602
>  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
>  _raw_spin_lock_irqsave+0x39/0x50 kernel/locking/spinlock.c:162
>  finish_wait+0xc0/0x270 kernel/sched/wait.c:400
>  inet_csk_wait_for_connect net/ipv4/inet_connection_sock.c:464 [inline]
>  inet_csk_accept+0x7de/0x9d0 net/ipv4/inet_connection_sock.c:497
>  mptcp_accept+0xe5/0x500 net/mptcp/protocol.c:2865
>  inet_accept+0xe4/0x7b0 net/ipv4/af_inet.c:739
>  mptcp_stream_accept+0x2e7/0x10e0 net/mptcp/protocol.c:3345
>  do_accept+0x382/0x510 net/socket.c:1773
>  __sys_accept4_file+0x7e/0xe0 net/socket.c:1816
>  __sys_accept4+0xb0/0x100 net/socket.c:1846
>  __do_sys_accept net/socket.c:1864 [inline]
>  __se_sys_accept net/socket.c:1861 [inline]
>  __x64_sys_accept+0x71/0xb0 net/socket.c:1861
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x7f177cd8b8e9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 b1 14 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f177cd3d308 EFLAGS: 00000246 ORIG_RAX: 000000000000002b
> RAX: ffffffffffffffda RBX: 00007f177ce13408 RCX: 00007f177cd8b8e9
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
> RBP: 00007f177ce13400 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f177ce1340c
> R13: 00007f177cde1004 R14: 6d705f706374706d R15: 0000000000022000
>  </TASK>
> 
> Fix the issue explicitly preventing the PM from closing subflows
> of MPTCP socket in listener status.
> 
> Reported-and-tested-by: syzbot+e4d843bb96a9431e6331@...kaller.appspotmail.com
> Fixes: 740d798e8767 ("mptcp: remove id 0 address")
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>

I'm dumb. We have likely a better fix for this one. I initially thought
it was not suitable for -net... as I was looking to the wrong patch :(

Self-nack, I'll test and send the other patch.

Sorry for the noise.

Paolo