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Date:   Mon, 30 Aug 2021 20:14:29 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     syzbot <syzbot+f9704d1878e290eddf73@...kaller.appspotmail.com>,
        andrii@...nel.org, asml.silence@...il.com, ast@...nel.org,
        bpf@...r.kernel.org, daniel@...earbox.net, davem@...emloft.net,
        dvyukov@...gle.com, io-uring@...r.kernel.org,
        john.fastabend@...il.com, kafai@...com, kpsingh@...nel.org,
        kuba@...nel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, songliubraving@...com,
        syzkaller-bugs@...glegroups.com, yhs@...com,
        Hao Xu <haoxu@...ux.alibaba.com>
Subject: Re: [syzbot] general protection fault in sock_from_file

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@...kaller.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@...ux.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?

-- 
Jens Axboe

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