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Subject: Re: [syzbot] general protection fault in sock_from_file
To:     Pavel Begunkov <asml.silence@gmail.com>,
        Jens Axboe <axboe@kernel.dk>,
        syzbot <syzbot+f9704d1878e290eddf73@syzkaller.appspotmail.com>,
        andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org,
        daniel@iogearbox.net, davem@davemloft.net, dvyukov@google.com,
        io-uring@vger.kernel.org, john.fastabend@gmail.com, kafai@fb.com,
        kpsingh@kernel.org, kuba@kernel.org, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, songliubraving@fb.com,
        syzkaller-bugs@googlegroups.com, yhs@fb.com
References: <00000000000059117905cacce99e@google.com>
 <7949b7a0-fec1-34a7-aaf5-cbe07c6127ed@kernel.dk>
 <d881d3fa-4df5-1862-bc2b-9420649ba3c8@linux.alibaba.com>
 <407ce02f-7a0a-4eb2-b242-188fc605012c@gmail.com>
 <6df81737-38d8-4c91-358a-79bc5d5f9074@linux.alibaba.com>
 <fb5821b5-3bb2-4c1a-acdb-816e639cb210@gmail.com>
From:   Hao Xu <haoxu@linux.alibaba.com>
Message-ID: <6a0ac681-3741-373c-6001-20af97aa5ea8@linux.alibaba.com>
Date:   Tue, 31 Aug 2021 19:48:07 +0800
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在 2021/8/31 下午7:26, Pavel Begunkov 写道:
> On 8/31/21 12:05 PM, Hao Xu wrote:
>> 在 2021/8/31 下午5:42, Pavel Begunkov 写道:
>>> On 8/31/21 10:19 AM, Hao Xu wrote:
>>>> 在 2021/8/31 上午10:14, Jens Axboe 写道:
>>>>> On 8/30/21 2:45 PM, syzbot wrote:
>>>>>> syzbot has found a reproducer for the following issue on:
>>>>>>
>>>>>> HEAD commit:    93717cde744f Add linux-next specific files for 20210830
>>>>>> git tree:       linux-next
>>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=15200fad300000
>>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=c643ef5289990dd1
>>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=f9704d1878e290eddf73
>>>>>> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
>>>>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=111f5f9d300000
>>>>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1651a415300000
>>>>>>
>>>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>>>>> Reported-by: syzbot+f9704d1878e290eddf73@syzkaller.appspotmail.com
>>>>>>
>>>>>> general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN
>>>>>> KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
>>>>>> CPU: 0 PID: 6548 Comm: syz-executor433 Not tainted 5.14.0-next-20210830-syzkaller #0
>>>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>>>>>> RIP: 0010:sock_from_file+0x20/0x90 net/socket.c:505
>>>>>> Code: f5 ff ff ff c3 0f 1f 44 00 00 41 54 53 48 89 fb e8 85 e9 62 fa 48 8d 7b 28 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 4f 45 31 e4 48 81 7b 28 80 f1 8a 8a 74 0c e8 58 e9
>>>>>> RSP: 0018:ffffc90002caf8e8 EFLAGS: 00010206
>>>>>> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
>>>>>> RDX: 0000000000000005 RSI: ffffffff8713203b RDI: 0000000000000028
>>>>>> RBP: ffff888019fc0780 R08: ffffffff899aee40 R09: ffffffff81e21978
>>>>>> R10: 0000000000000027 R11: 0000000000000009 R12: dffffc0000000000
>>>>>> R13: 1ffff110033f80f9 R14: 0000000000000003 R15: ffff888019fc0780
>>>>>> FS:  00000000013b5300(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
>>>>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>>> CR2: 00000000004ae0f0 CR3: 000000001d355000 CR4: 00000000001506f0
>>>>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>>>>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>>>>> Call Trace:
>>>>>>     io_sendmsg+0x98/0x640 fs/io_uring.c:4681
>>>>>>     io_issue_sqe+0x14de/0x6ba0 fs/io_uring.c:6578
>>>>>>     __io_queue_sqe+0x90/0xb50 fs/io_uring.c:6864
>>>>>>     io_req_task_submit+0xbf/0x1b0 fs/io_uring.c:2218
>>>>>>     tctx_task_work+0x166/0x610 fs/io_uring.c:2143
>>>>>>     task_work_run+0xdd/0x1a0 kernel/task_work.c:164
>>>>>>     tracehook_notify_signal include/linux/tracehook.h:212 [inline]
>>>>>>     handle_signal_work kernel/entry/common.c:146 [inline]
>>>>>>     exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
>>>>>>     exit_to_user_mode_prepare+0x256/0x290 kernel/entry/common.c:209
>>>>>>     __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
>>>>>>     syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:302
>>>>>>     do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
>>>>>>     entry_SYSCALL_64_after_hwframe+0x44/0xae
>>>>>> RIP: 0033:0x43fd49
>>>>>
>>>>> Hao, this is due to:
>>>>>
>>>>> commit a8295b982c46d4a7c259a4cdd58a2681929068a9
>>>>> Author: Hao Xu <haoxu@linux.alibaba.com>
>>>>> Date:   Fri Aug 27 17:46:09 2021 +0800
>>>>>
>>>>>        io_uring: fix failed linkchain code logic
>>>>>
>>>>> which causes some weirdly super long chains from that single sqe.
>>>>> Can you take a look, please?
>>>> Sure, I'm working on this.
>>>
>>> Ah, saw it after sending a patch. It's nothing too curious, just
>>> a small error in logic. More interesting that we don't have a
>>> test case covering it, we should definitely add something.
>>>
>> Saw your patch after coding my fix..????
>> Since my email client doesn't receive your patch(only saw it in
>> webpage https://lore.kernel.org/), I put my comment here:
> 
> Hmm, does it happen often? I'll CC you
Uncommon, somestimes there is delay.
> 
> 
>>>   fs/io_uring.c | 2 ++
>>>   1 file changed, 2 insertions(+)
>>>
>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>> index 473a977c7979..a531c7324ea8 100644
>>> --- a/fs/io_uring.c
>>> +++ b/fs/io_uring.c
>>> @@ -6717,6 +6717,8 @@ static inline void io_queue_sqe(struct io_kiocb *req)
>>>       if (likely(!(req->flags & (REQ_F_FORCE_ASYNC | REQ_F_FAIL)))) {
>>>           __io_queue_sqe(req);
>>>       } else if (req->flags & REQ_F_FAIL) {
>>> +        /* fail all, we don't submit */
>>> +        req->flags &= ~REQ_F_HARDLINK;
>> maybe set REQ_F_LINK here?
> 
> if (unlikely((req->flags & REQ_F_FAIL) &&
> 	     !(req->flags & REQ_F_HARDLINK))) {
> 	posted |= (req->link != NULL);
> 	io_fail_links(req);
> }
> 
> The problem is hardlink, normal will be failed. But there is indeed
> a problem with both patches,
> 
> if (req->flags & (REQ_F_LINK | REQ_F_HARDLINK))
> 	// kill linked
Yeah, if we don't have REQ_F_LINK, io_req_complete_post() won't go to
the disarm branch
> 
> Will resend with some tests on top
> 
> 
>>>           io_req_complete_failed(req, req->result);
>>>       } else {
>>>           int ret = io_req_prep_async(req);
>