Re: [syzbot] [fs?] WARNING in handle_userfault

[Suren Baghdasaryan]

On Wed, Jul 5, 2023 at 6:16 AM syzbot
<syzbot+339b02f826caafd5f7a8@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> syzbot has found a reproducer for the following issue on:
>
> HEAD commit:    e1f6a8eaf1c2 Add linux-next specific files for 20230705
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=13ec5228a80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=347a3e7e531c1809
> dashboard link: https://syzkaller.appspot.com/bug?extid=339b02f826caafd5f7a8
> 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=1716aeaca80000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12e882e2a80000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/2d0435d8ff5d/disk-e1f6a8ea.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/d28b2df82094/vmlinux-e1f6a8ea.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/fb4e5bfa0a0f/bzImage-e1f6a8ea.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+339b02f826caafd5f7a8@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> kvm_intel: L1TF CPU bug present and SMT on, data leak possible. See CVE-2018-3646 and https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1tf.html for details.
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 5028 at include/linux/mmap_lock.h:71 mmap_assert_write_locked include/linux/mmap_lock.h:71 [inline]
> WARNING: CPU: 0 PID: 5028 at include/linux/mmap_lock.h:71 __is_vma_write_locked include/linux/mm.h:712 [inline]
> WARNING: CPU: 0 PID: 5028 at include/linux/mmap_lock.h:71 vma_assert_locked include/linux/mm.h:753 [inline]
> WARNING: CPU: 0 PID: 5028 at include/linux/mmap_lock.h:71 assert_fault_locked include/linux/mm.h:786 [inline]
> WARNING: CPU: 0 PID: 5028 at include/linux/mmap_lock.h:71 handle_userfault+0x149b/0x27a0 fs/userfaultfd.c:440
> Modules linked in:
> CPU: 0 PID: 5028 Comm: syz-executor359 Not tainted 6.4.0-next-20230705-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
> RIP: 0010:mmap_assert_write_locked include/linux/mmap_lock.h:71 [inline]
> RIP: 0010:__is_vma_write_locked include/linux/mm.h:712 [inline]
> RIP: 0010:vma_assert_locked include/linux/mm.h:753 [inline]
> RIP: 0010:assert_fault_locked include/linux/mm.h:786 [inline]
> RIP: 0010:handle_userfault+0x149b/0x27a0 fs/userfaultfd.c:440
> Code: ff 49 8d bc 24 a0 01 00 00 31 f6 e8 2f b9 23 08 31 ff 41 89 c5 89 c6 e8 c3 a2 87 ff 45 85 ed 0f 85 83 ed ff ff e8 95 a6 87 ff <0f> 0b e9 77 ed ff ff e8 89 a6 87 ff 49 8d bc 24 a0 01 00 00 be ff
> RSP: 0000:ffffc90003a4fb68 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: ffffc90003a4fd88 RCX: 0000000000000000
> RDX: ffff8880133bbb80 RSI: ffffffff81fd6ddb RDI: 0000000000000005
> RBP: 0000000000000200 R08: 0000000000000005 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000001 R12: ffff88807d8e4280
> R13: 0000000000000000 R14: ffff888021cb9110 R15: ffff888021cb9100
> FS:  000055555738f300(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020b7d800 CR3: 0000000029d0e000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  do_anonymous_page mm/memory.c:4151 [inline]
>  do_pte_missing mm/memory.c:3671 [inline]
>  handle_pte_fault mm/memory.c:4949 [inline]
>  __handle_mm_fault+0x35ff/0x3cc0 mm/memory.c:5089
>  handle_mm_fault+0x3c2/0xa20 mm/memory.c:5254
>  do_user_addr_fault+0x2ed/0x13a0 arch/x86/mm/fault.c:1365
>  handle_page_fault arch/x86/mm/fault.c:1509 [inline]
>  exc_page_fault+0x98/0x170 arch/x86/mm/fault.c:1565
>  asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:570
> RIP: 0033:0x7faa694e34d5
> Code: 52 89 c2 01 f6 29 f2 83 fa 05 0f 87 0a 02 00 00 48 63 14 97 48 01 fa ff e2 0f 1f 40 00 4c 89 d2 66 c1 e9 03 83 c0 01 0f b7 c9 <48> 89 14 cd 00 d8 b7 20 83 f8 20 75 b6 48 8b 84 24 f0 00 00 00 f3
> RSP: 002b:00007ffefcb0d8e0 EFLAGS: 00010202
> RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000860000109120 RSI: 0000000000000000 RDI: 00007faa69564020
> RBP: 0000000000000006 R08: 0000830000789120 R09: 00000000aaaaaaab
> R10: 0000870000109120 R11: 00008f0000309120 R12: 00008b0000889120
> R13: 0000000000000000 R14: 00008e0000309120 R15: 00007ffefcb0de40
>  </TASK>
>

Sorry, this is my code. Missed that __is_vma_write_locked() generates
assertion. Will post a fix shortly.

>
> ---
> 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.