Subject: Re: net: BUG in unix_notinflight
To: Cong Wang <xiyou.wangcong@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>
References: <CACT4Y+b5_zcRVrq5yRmtkVUgnzOmq55upA_QCoLrkSDnT0cLHA@mail.gmail.com>
 <CACT4Y+bCvPdn3i-nuBCbPyHUuOjyh83KyLFzWR+8JDGqM0F2ww@mail.gmail.com>
 <CAM_iQpWePCJ3oyOf8xRdJ5CtPMR6UNvNKs7t=MabtL=obGoSxg@mail.gmail.com>
Cc: David Miller <davem@davemloft.net>,
        Hannes Frederic Sowa <hannes@stressinduktion.org>,
        Willy Tarreau <w@1wt.eu>, netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Eric Dumazet <edumazet@google.com>, Al Viro <viro@zeniv.linux.org.uk>,
        syzkaller <syzkaller@googlegroups.com>
From: Nikolay Borisov <n.borisov.lkml@gmail.com>
Message-ID: <74aac97b-f779-1554-a34b-bca173ab0c8d@gmail.com>
Date: Wed, 8 Mar 2017 00:23:56 +0200
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>>
>>
>> New report from linux-next/c0b7b2b33bd17f7155956d0338ce92615da686c9
>>
>> ------------[ cut here ]------------
>> kernel BUG at net/unix/garbage.c:149!
>> invalid opcode: 0000 [#1] SMP KASAN
>> Dumping ftrace buffer:
>>    (ftrace buffer empty)
>> Modules linked in:
>> CPU: 0 PID: 1806 Comm: syz-executor7 Not tainted 4.10.0-next-20170303+ #6
>> Hardware name: Google Google Compute Engine/Google Compute Engine,
>> BIOS Google 01/01/2011
>> task: ffff880121c64740 task.stack: ffff88012c9e8000
>> RIP: 0010:unix_notinflight+0x417/0x5d0 net/unix/garbage.c:149
>> RSP: 0018:ffff88012c9ef0f8 EFLAGS: 00010297
>> RAX: ffff880121c64740 RBX: 1ffff1002593de23 RCX: ffff8801c490c628
>> RDX: 0000000000000000 RSI: 1ffff1002593de27 RDI: ffffffff8557e504
>> RBP: ffff88012c9ef220 R08: 0000000000000001 R09: 0000000000000000
>> R10: dffffc0000000000 R11: ffffed002593de55 R12: ffff8801c490c0c0
>> R13: ffff88012c9ef1f8 R14: ffffffff85101620 R15: dffffc0000000000
>> FS:  00000000013d3940(0000) GS:ffff8801dbe00000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 0000000001fd8cd8 CR3: 00000001cce69000 CR4: 00000000001426f0
>> Call Trace:
>>  unix_detach_fds.isra.23+0xfa/0x170 net/unix/af_unix.c:1490
>>  unix_destruct_scm+0xf4/0x200 net/unix/af_unix.c:1499
> 
> The problem here is there is no lock protecting concurrent unix_detach_fds()
> even though unix_notinflight() is already serialized, if we call
> unix_notinflight()
> twice on the same file pointer, we trigger this bug...
> 
> I don't know what is the right lock here to serialize it.
> 


I reported something similar a while ago
https://lists.gt.net/linux/kernel/2534612

And Miklos Szeredi then produced the following patch :

https://patchwork.kernel.org/patch/9305121/

However, this was never applied. I wonder if the patch makes sense?