Message-ID: <2db3c803-6a94-9345-261a-a2bb74370c02@redhat.com>
Date:   Tue, 30 Mar 2021 19:04:30 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     syzbot <syzbot+015dd7cdbbbc2c180c65@...kaller.appspotmail.com>,
        akpm@...ux-foundation.org, bp@...en8.de, daniel.vetter@...ll.ch,
        daniel.vetter@...el.com, hpa@...or.com, jmattson@...gle.com,
        jmorris@...ei.org, joro@...tes.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-mm@...ck.org, linux-security-module@...r.kernel.org,
        m.szyprowski@...sung.com, mchehab@...nel.org, mingo@...hat.com,
        seanjc@...gle.com, serge@...lyn.com,
        syzkaller-bugs@...glegroups.com, tfiga@...omium.org,
        tglx@...utronix.de, vkuznets@...hat.com, wanpengli@...cent.com,
        x86@...nel.org
Subject: Re: [syzbot] WARNING in unsafe_follow_pfn

On 30/03/21 17:26, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    93129492 Add linux-next specific files for 20210326
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=169ab21ad00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6f2f73285ea94c45
> dashboard link: https://syzkaller.appspot.com/bug?extid=015dd7cdbbbc2c180c65
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=119b8d06d00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=112e978ad00000
> 
> The issue was bisected to:
> 
> commit d40b9fdee6dc819d8fc35f70c345cbe0394cde4c
> Author: Daniel Vetter <daniel.vetter@...ll.ch>
> Date:   Tue Mar 16 15:33:01 2021 +0000
> 
>      mm: Add unsafe_follow_pfn
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=122d2016d00000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=112d2016d00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=162d2016d00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+015dd7cdbbbc2c180c65@...kaller.appspotmail.com
> Fixes: d40b9fdee6dc ("mm: Add unsafe_follow_pfn")

This is basically intentional because get_vaddr_frames is broken, isn't 
it?  I think it needs to be ignored in syzkaller.

Paolo

> ------------[ cut here ]------------
> unsafe follow_pfn usage
> WARNING: CPU: 1 PID: 8426 at mm/memory.c:4807 unsafe_follow_pfn+0x20f/0x260 mm/memory.c:4807
> Modules linked in:
> CPU: 0 PID: 8426 Comm: syz-executor677 Not tainted 5.12.0-rc4-next-20210326-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:unsafe_follow_pfn+0x20f/0x260 mm/memory.c:4807
> Code: 8b 7c 24 20 49 89 6d 00 e8 6e 84 64 07 e9 30 ff ff ff e8 f4 19 cb ff 48 c7 c7 40 1f 76 89 c6 05 56 eb 09 0c 01 e8 34 1a 21 07 <0f> 0b e9 71 fe ff ff 41 bc ea ff ff ff e9 06 ff ff ff e8 1a 65 0f
> RSP: 0018:ffffc9000161f660 EFLAGS: 00010282
> RAX: 0000000000000000 RBX: 1ffff920002c3ecc RCX: 0000000000000000
> RDX: ffff88801954d580 RSI: ffffffff815c3fd5 RDI: fffff520002c3ebe
> RBP: ffff888023d56948 R08: 0000000000000000 R09: 0000000000000000
> R10: ffffffff815bd77e R11: 0000000000000000 R12: 0000000021000000
> R13: ffff8880143a4010 R14: 0000000000000000 R15: 0000000000000110
> FS:  00000000005d1300(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f172c4cd6c0 CR3: 0000000011f70000 CR4: 00000000001506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   get_vaddr_frames+0x337/0x600 drivers/media/common/videobuf2/frame_vector.c:72
>   vb2_create_framevec+0x55/0xc0 drivers/media/common/videobuf2/videobuf2-memops.c:50
>   vb2_vmalloc_get_userptr+0xce/0x4c0 drivers/media/common/videobuf2/videobuf2-vmalloc.c:90
>   __prepare_userptr+0x342/0x15f0 drivers/media/common/videobuf2/videobuf2-core.c:1128
>   __buf_prepare+0x635/0x7d0 drivers/media/common/videobuf2/videobuf2-core.c:1367
>   vb2_core_qbuf+0xa9d/0x11c0 drivers/media/common/videobuf2/videobuf2-core.c:1658
>   vb2_qbuf+0x135/0x1a0 drivers/media/common/videobuf2/videobuf2-v4l2.c:820
>   vb2_ioctl_qbuf+0xfb/0x140 drivers/media/common/videobuf2/videobuf2-v4l2.c:1050
>   v4l_qbuf drivers/media/v4l2-core/v4l2-ioctl.c:2027 [inline]
>   v4l_qbuf+0x92/0xc0 drivers/media/v4l2-core/v4l2-ioctl.c:2021
>   __video_do_ioctl+0xb94/0xe20 drivers/media/v4l2-core/v4l2-ioctl.c:2951
>   video_usercopy+0x253/0x1300 drivers/media/v4l2-core/v4l2-ioctl.c:3297
>   v4l2_ioctl+0x1b3/0x250 drivers/media/v4l2-core/v4l2-dev.c:366
>   vfs_ioctl fs/ioctl.c:48 [inline]
>   __do_sys_ioctl fs/ioctl.c:753 [inline]
>   __se_sys_ioctl fs/ioctl.c:739 [inline]
>   __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
>   do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>   entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x443639
> 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:00007ffee3065668 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000443639
> RDX: 0000000020000140 RSI: 00000000c058560f RDI: 0000000000000004
> RBP: 00000000004031e0 R08: 00000000004004a0 R09: 00000000004004a0
> R10: 00236962762f7665 R11: 0000000000000246 R12: 0000000000403270
> R13: 0000000000000000 R14: 00000000004b1018 R15: 00000000004004a0
> 
> 
> ---
> 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.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches
> 

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