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    Subject[syzbot] general protection fault in snd_virmidi_output_trigger
    From
    Hello,

    syzbot found the following issue on:

    HEAD commit: 952923ddc011 Merge tag 'pull-18-rc1-work.namei' of git://g..
    git tree: upstream
    console output: https://syzkaller.appspot.com/x/log.txt?x=10b95d0bf00000
    kernel config: https://syzkaller.appspot.com/x/.config?x=3096247591885bfa
    dashboard link: https://syzkaller.appspot.com/bug?extid=8e407e6b1dba0a275884
    compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

    Unfortunately, I don't have any reproducer for this issue yet.

    IMPORTANT: if you fix the issue, please add the following tag to the commit:
    Reported-by: syzbot+8e407e6b1dba0a275884@syzkaller.appspotmail.com

    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: 18021 Comm: syz-executor.1 Not tainted 5.18.0-syzkaller-13842-g952923ddc011 #0
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
    RIP: 0010:snd_virmidi_output_trigger+0x82/0x130 sound/core/seq/seq_virmidi.c:169
    Code: 8b ad 30 01 00 00 31 ff 89 de e8 d9 8b 4f fa 85 db 48 b8 00 00 00 00 00 fc ff df 41 0f 95 c4 48 8d 7d 1c 48 89 fa 48 c1 ea 03 <0f> b6 04 02 48 89 fa 83 e2 07 38 d0 7f 04 84 c0 75 60 31 ff 44 88
    RSP: 0018:ffffc9000c6e7c48 EFLAGS: 00010207
    RAX: dffffc0000000000 RBX: 0000000000000001 RCX: ffffffff872af747
    RDX: 0000000000000003 RSI: 0000000000000000 RDI: 000000000000001c
    RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000
    R10: 0000000000000001 R11: 0000000000000001 R12: ffff888078d6c801
    R13: 000000007f012000 R14: ffff88814ab3c400 R15: 0000000000001000
    FS: 00007fc5b5868700(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 0000000020fec000 CR3: 0000000046903000 CR4: 00000000003506e0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
    <TASK>
    snd_rawmidi_output_trigger sound/core/rawmidi.c:186 [inline]
    snd_rawmidi_output_trigger sound/core/rawmidi.c:182 [inline]
    snd_rawmidi_kernel_write1+0x548/0x870 sound/core/rawmidi.c:1502
    snd_rawmidi_write+0x273/0xb90 sound/core/rawmidi.c:1555
    vfs_write+0x269/0xac0 fs/read_write.c:589
    ksys_write+0x1e8/0x250 fs/read_write.c:644
    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+0x46/0xb0
    RIP: 0033:0x7fc5b4689109
    Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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:00007fc5b5868168 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
    RAX: ffffffffffffffda RBX: 00007fc5b479bf60 RCX: 00007fc5b4689109
    RDX: 00000000fffffd2c RSI: 0000000020000000 RDI: 0000000000000004
    RBP: 00007fc5b46e308d R08: 0000000000000000 R09: 0000000000000000
    R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
    R13: 00007fc5b4ccfb1f R14: 00007fc5b5868300 R15: 0000000000022000
    </TASK>
    Modules linked in:
    ---[ end trace 0000000000000000 ]---
    RIP: 0010:snd_virmidi_output_trigger+0x82/0x130 sound/core/seq/seq_virmidi.c:169
    Code: 8b ad 30 01 00 00 31 ff 89 de e8 d9 8b 4f fa 85 db 48 b8 00 00 00 00 00 fc ff df 41 0f 95 c4 48 8d 7d 1c 48 89 fa 48 c1 ea 03 <0f> b6 04 02 48 89 fa 83 e2 07 38 d0 7f 04 84 c0 75 60 31 ff 44 88
    RSP: 0018:ffffc9000c6e7c48 EFLAGS: 00010207
    RAX: dffffc0000000000 RBX: 0000000000000001 RCX: ffffffff872af747
    RDX: 0000000000000003 RSI: 0000000000000000 RDI: 000000000000001c
    RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000
    R10: 0000000000000001 R11: 0000000000000001 R12: ffff888078d6c801
    R13: 000000007f012000 R14: ffff88814ab3c400 R15: 0000000000001000
    FS: 00007fc5b5868700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 0000001b2bc27000 CR3: 0000000046903000 CR4: 00000000003506f0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    ----------------
    Code disassembly (best guess):
    0: 8b ad 30 01 00 00 mov 0x130(%rbp),%ebp
    6: 31 ff xor %edi,%edi
    8: 89 de mov %ebx,%esi
    a: e8 d9 8b 4f fa callq 0xfa4f8be8
    f: 85 db test %ebx,%ebx
    11: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
    18: fc ff df
    1b: 41 0f 95 c4 setne %r12b
    1f: 48 8d 7d 1c lea 0x1c(%rbp),%rdi
    23: 48 89 fa mov %rdi,%rdx
    26: 48 c1 ea 03 shr $0x3,%rdx
    * 2a: 0f b6 04 02 movzbl (%rdx,%rax,1),%eax <-- trapping instruction
    2e: 48 89 fa mov %rdi,%rdx
    31: 83 e2 07 and $0x7,%edx
    34: 38 d0 cmp %dl,%al
    36: 7f 04 jg 0x3c
    38: 84 c0 test %al,%al
    3a: 75 60 jne 0x9c
    3c: 31 ff xor %edi,%edi
    3e: 44 rex.R
    3f: 88 .byte 0x88


    ---
    This report is generated by a bot. It may contain errors.
    See https://goo.gl/tpsmEJ for more information about syzbot.
    syzbot engineers can be reached at syzkaller@googlegroups.com.

    syzbot will keep track of this issue. See:
    https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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