Re: [syzbot] [mm?] kernel BUG in move_pages

[Suren Baghdasaryan <surenb@google.com>]

On Thu, Jan 11, 2024 at 8:25 AM syzbot
<syzbot+705209281e36404998f6@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    e2425464bc87 Add linux-next specific files for 20240105
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14941cdee80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4056b9349f3da8c9
> dashboard link: https://syzkaller.appspot.com/bug?extid=705209281e36404998f6
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=125d0a09e80000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15bc7331e80000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/2f738185e2cf/disk-e2425464.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/b248fcf4ea46/vmlinux-e2425464.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/a9945c8223f4/bzImage-e2425464.xz
>
> The issue was bisected to:
>
> commit adef440691bab824e39c1b17382322d195e1fab0
> Author: Andrea Arcangeli <aarcange@redhat.com>
> Date:   Wed Dec 6 10:36:56 2023 +0000
>
>     userfaultfd: UFFDIO_MOVE uABI
>
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11cb6ea9e80000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=13cb6ea9e80000
> console output: https://syzkaller.appspot.com/x/log.txt?x=15cb6ea9e80000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com
> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
>
>  do_one_initcall+0x128/0x680 init/main.c:1237
>  do_initcall_level init/main.c:1299 [inline]
>  do_initcalls init/main.c:1315 [inline]
>  do_basic_setup init/main.c:1334 [inline]
>  kernel_init_freeable+0x692/0xc30 init/main.c:1552
>  kernel_init+0x1c/0x2a0 init/main.c:1442
>  ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
> ------------[ cut here ]------------
> kernel BUG at include/linux/page-flags.h:1035!
> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 5068 Comm: syz-executor191 Not tainted 6.7.0-rc8-next-20240105-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]

From a quick look, I think the new ioctl is being used against a
file-backed page and that's why PageAnonExclusive() throws this error.
I'll confirm if this is indeed the case and will add checks for that
case. Thanks!

> RIP: 0010:move_pages+0x1697/0x3d40 mm/userfaultfd.c:1402
> Code: 00 00 48 c1 e8 0c 48 21 d0 48 c1 e0 06 48 01 c3 e9 b6 f7 ff ff e8 79 c6 9c ff 48 c7 c6 e0 7e dc 8a 48 89 df e8 0a 20 dc ff 90 <0f> 0b e8 62 c6 9c ff 48 89 da b8 ff ff 37 00 48 c1 ea 03 48 c1 e0
> RSP: 0018:ffffc90003aefa98 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: ffffea0001e40000 RCX: ffffffff81687599
> RDX: ffff88802a155940 RSI: ffffffff81eb5d46 RDI: 0000000000000000
> RBP: ffff88802abab810 R08: 0000000000000000 R09: fffffbfff1e75fda
> R10: ffffffff8f3afed7 R11: 0000000000000001 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000020518000 R15: 0000000000000000
> FS:  00005555562cf380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000204f8000 CR3: 000000006a725000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  userfaultfd_move fs/userfaultfd.c:2047 [inline]
>  userfaultfd_ioctl+0x683/0x6420 fs/userfaultfd.c:2169
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:871 [inline]
>  __se_sys_ioctl fs/ioctl.c:857 [inline]
>  __x64_sys_ioctl+0x18f/0x210 fs/ioctl.c:857
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xd0/0x250 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x62/0x6a
> RIP: 0033:0x7f4bada9b3e9
> Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 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 b8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fff2c1d6998 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007fff2c1d6b68 RCX: 00007f4bada9b3e9
> RDX: 00000000200000c0 RSI: 00000000c028aa05 RDI: 0000000000000003
> RBP: 00007f4badb0e610 R08: 00007fff2c1d6b68 R09: 00007fff2c1d6b68
> R10: 00007fff2c1d6b68 R11: 0000000000000246 R12: 0000000000000001
> R13: 00007fff2c1d6b58 R14: 0000000000000001 R15: 0000000000000001
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]
> RIP: 0010:move_pages+0x1697/0x3d40 mm/userfaultfd.c:1402
> Code: 00 00 48 c1 e8 0c 48 21 d0 48 c1 e0 06 48 01 c3 e9 b6 f7 ff ff e8 79 c6 9c ff 48 c7 c6 e0 7e dc 8a 48 89 df e8 0a 20 dc ff 90 <0f> 0b e8 62 c6 9c ff 48 89 da b8 ff ff 37 00 48 c1 ea 03 48 c1 e0
> RSP: 0018:ffffc90003aefa98 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: ffffea0001e40000 RCX: ffffffff81687599
> RDX: ffff88802a155940 RSI: ffffffff81eb5d46 RDI: 0000000000000000
> RBP: ffff88802abab810 R08: 0000000000000000 R09: fffffbfff1e75fda
> R10: ffffffff8f3afed7 R11: 0000000000000001 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000020518000 R15: 0000000000000000
> FS:  00005555562cf380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000204f8000 CR3: 000000006a725000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>
>
> ---
> This report is generated by a bot. It may contain errors.
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