Date:   Fri, 14 Jul 2023 08:53:17 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     syzbot <syzbot+42309678e0bc7b32f8e9@...kaller.appspotmail.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        syzkaller-bugs@...glegroups.com,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Peter Xu <peterx@...hat.com>
Subject: Re: [syzbot] [mm?] kernel BUG in mfill_atomic_copy

On Thu, 13 Jul 2023 20:34:45 -0700 syzbot <syzbot+42309678e0bc7b32f8e9@...kaller.appspotmail.com> wrote:

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    fe57d0d86f03 Add linux-next specific files for 20230710
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14d46ed8a80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=eaa6217eed71d333
> dashboard link: https://syzkaller.appspot.com/bug?extid=42309678e0bc7b32f8e9
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14b63e18a80000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13784d64a80000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/9e7627fb1623/disk-fe57d0d8.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/848a690045db/vmlinux-fe57d0d8.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/36e5c3ae635e/bzImage-fe57d0d8.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+42309678e0bc7b32f8e9@...kaller.appspotmail.com
> 
> ------------[ cut here ]------------
> kernel BUG at mm/userfaultfd.c:573!

Thanks.  cc's added.

> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> CPU: 1 PID: 5031 Comm: syz-executor410 Not tainted 6.5.0-rc1-next-20230710-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/03/2023
> RIP: 0010:mfill_atomic mm/userfaultfd.c:573 [inline]
> RIP: 0010:mfill_atomic_copy+0x9ed/0x17e0 mm/userfaultfd.c:725
> Code: 8d 8c 24 a8 00 00 00 4c 89 e7 e8 be 54 d9 ff 4c 63 f0 e9 71 fc ff ff e8 51 eb a1 ff 0f 0b e8 4a eb a1 ff 0f 0b e8 43 eb a1 ff <0f> 0b e8 3c eb a1 ff 0f 0b 49 c7 c6 ef ff ff ff e9 54 fd ff ff e8
> RSP: 0018:ffffc9000395fb48 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: dffffc0000000000 RCX: 0000000000000000
> RDX: ffff88801f67bb80 RSI: ffffffff81e32bad RDI: 0000000000000006
> RBP: 0000000000000000 R08: 0000000000000006 R09: ffffffffffffffff
> R10: 0000000005ffffff R11: 0000000000000001 R12: 0000200000000000
> R13: 00005ffffffff001 R14: ffffffffffffffff R15: 0000000005ffffff
> FS:  00005555571e03c0(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020000060 CR3: 000000002ba7a000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  userfaultfd_copy fs/userfaultfd.c:1766 [inline]
>  userfaultfd_ioctl+0xe43/0x4c40 fs/userfaultfd.c:2098
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:870 [inline]
>  __se_sys_ioctl fs/ioctl.c:856 [inline]
>  __x64_sys_ioctl+0x19d/0x210 fs/ioctl.c:856
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f2e41c4b4b9
> Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 00 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 c0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fff13a95188 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007fff13a95198 RCX: 00007f2e41c4b4b9
> RDX: 0000000020000040 RSI: 00000000c028aa03 RDI: 0000000000000003
> RBP: 00007fff13a95190 R08: 00007fff13a95190 R09: 00007f2e41c0e380
> R10: 00007fff13a95190 R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:mfill_atomic mm/userfaultfd.c:573 [inline]
> RIP: 0010:mfill_atomic_copy+0x9ed/0x17e0 mm/userfaultfd.c:725
> Code: 8d 8c 24 a8 00 00 00 4c 89 e7 e8 be 54 d9 ff 4c 63 f0 e9 71 fc ff ff e8 51 eb a1 ff 0f 0b e8 4a eb a1 ff 0f 0b e8 43 eb a1 ff <0f> 0b e8 3c eb a1 ff 0f 0b 49 c7 c6 ef ff ff ff e9 54 fd ff ff e8
> RSP: 0018:ffffc9000395fb48 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: dffffc0000000000 RCX: 0000000000000000
> RDX: ffff88801f67bb80 RSI: ffffffff81e32bad RDI: 0000000000000006
> RBP: 0000000000000000 R08: 0000000000000006 R09: ffffffffffffffff
> R10: 0000000005ffffff R11: 0000000000000001 R12: 0000200000000000
> R13: 00005ffffffff001 R14: ffffffffffffffff R15: 0000000005ffffff
> FS:  00005555571e03c0(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020000060 CR3: 000000002ba7a000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 
> 
> ---
> 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@...glegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 
> If the bug is already fixed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
> 
> If you want to change bug's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
> 
> If the bug is a duplicate of another bug, reply with:
> #syz dup: exact-subject-of-another-report
> 
> If you want to undo deduplication, reply with:
> #syz undup

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