I think this is the problem Peter Xu pointed out, and has been fixed in v2 of the patch (which has us return -EFAULT instead of -ENOENT). I think this based on: This page has a link to the line on which the bug happened: https://syzkaller.appspot.com/bug?extid=3f1e5c1dea3a2e66ea9a It links to this line: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/mm/userfaultfd.c?id=6d0c806803170f120f8cb97b321de7bd89d3a791#n642 So, it seems this is the BUG that was triggered: if (unlikely(err == -ENOENT)) { BUG_ON(!page); } On Mon, Jun 13, 2022 at 10:41 AM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Sun, 12 Jun 2022 23:47:26 -0700 syzbot <syzbot+3f1e5c1dea3a2e66ea9a@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: 6d0c80680317 Add linux-next specific files for 20220610 > > git tree: linux-next > > console output: https://syzkaller.appspot.com/x/log.txt?x=13a777f7f00000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=a30d6e3e814e5931 > > dashboard link: https://syzkaller.appspot.com/bug?extid=3f1e5c1dea3a2e66ea9a > > 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+3f1e5c1dea3a2e66ea9a@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > ------------[ cut here ]------------ > > kernel BUG at mm/userfaultfd.c:642! > > Thanks. I'm looking suspiciously at "mm: userfaultfd: fix > UFFDIO_CONTINUE on fallocated shmem pages"? > > > invalid opcode: 0000 [#1] PREEMPT SMP KASAN > > CPU: 0 PID: 14685 Comm: syz-executor.4 Not tainted 5.19.0-rc1-next-20220610-syzkaller #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > RIP: 0010:__mcopy_atomic mm/userfaultfd.c:642 [inline] > > RIP: 0010:mcopy_continue+0x80f/0x1360 mm/userfaultfd.c:699 > > Code: a8 ff 49 83 fd fe 0f 85 bd fd ff ff e8 ba ca a8 ff 0f 1f 44 00 00 e8 b0 ca a8 ff e8 ab ca a8 ff 48 8b 7c 24 20 e8 51 76 8b ff <0f> 0b e8 9a ca a8 ff 0f 0b e8 93 ca a8 ff 4d 89 ee 31 ff 41 81 e6 > > RSP: 0018:ffffc900058f7b70 EFLAGS: 00010282 > > RAX: 0000000000000000 RBX: ffff8880226dee58 RCX: 0000000000000000 > > RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffff88801a0b4228 > > RBP: 0000000020531000 R08: 0000000000000001 R09: ffff88801a0b422f > > R10: ffffed1003416845 R11: 0000000000000001 R12: 0000000000000000 > > R13: fffffffffffffffe R14: 00000000fffffffe R15: ffff88801a0b4140 > > FS: 00007f91409ee700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 0000001b2c522000 CR3: 000000001d578000 CR4: 00000000003526f0 > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > Call Trace: > > <TASK> > > userfaultfd_continue fs/userfaultfd.c:1893 [inline] > > userfaultfd_ioctl+0x1818/0x41f0 fs/userfaultfd.c:2017 > > 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+0x193/0x200 fs/ioctl.c:856 > > 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: 0033:0x7f913f889109 > > 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:00007f91409ee168 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 > > RAX: ffffffffffffffda RBX: 00007f913f99c030 RCX: 00007f913f889109 > > RDX: 0000000020000040 RSI: 00000000c020aa07 RDI: 0000000000000004 > > RBP: 00007f913f8e30ad R08: 0000000000000000 R09: 0000000000000000 > > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 > > R13: 00007ffcb29c401f R14: 00007f91409ee300 R15: 0000000000022000 > > </TASK> > > Modules linked in: > > ---[ end trace 0000000000000000 ]--- > > RIP: 0010:__mcopy_atomic mm/userfaultfd.c:642 [inline] > > RIP: 0010:mcopy_continue+0x80f/0x1360 mm/userfaultfd.c:699 > > Code: a8 ff 49 83 fd fe 0f 85 bd fd ff ff e8 ba ca a8 ff 0f 1f 44 00 00 e8 b0 ca a8 ff e8 ab ca a8 ff 48 8b 7c 24 20 e8 51 76 8b ff <0f> 0b e8 9a ca a8 ff 0f 0b e8 93 ca a8 ff 4d 89 ee 31 ff 41 81 e6 > > RSP: 0018:ffffc900058f7b70 EFLAGS: 00010282 > > RAX: 0000000000000000 RBX: ffff8880226dee58 RCX: 0000000000000000 > > RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffff88801a0b4228 > > RBP: 0000000020531000 R08: 0000000000000001 R09: ffff88801a0b422f > > R10: ffffed1003416845 R11: 0000000000000001 R12: 0000000000000000 > > R13: fffffffffffffffe R14: 00000000fffffffe R15: ffff88801a0b4140 > > FS: 00007f91409ee700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 00007f91409cd718 CR3: 000000001d578000 CR4: 00000000003526f0 > > 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@xxxxxxxxxxxxxxxx. > > > > syzbot will keep track of this issue. See: > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
