Re: [syzbot] WARNING in vma_merge

[Andrew Morton]

On Wed, 27 Apr 2022 06:15:20 -0700 syzbot <syzbot+7728e4ab5371cebc9c00@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

> syzbot has found a reproducer for the following issue on:

Thanks.

userfaultfd_release() appears to have offended vma_merge().

I'm not seeing any changes in that area from Peter, but Liam's
mapletree work changed things around a bit.  Gents, could you please
take a look?


> HEAD commit:    f02ac5c95dfd Add linux-next specific files for 20220427
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=105a33a2f00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=e9256c70f586da8a
> dashboard link: https://syzkaller.appspot.com/bug?extid=7728e4ab5371cebc9c00
> 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=15f76f82f00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12b42c3cf00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+7728e4ab5371cebc9c00@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 3593 at mm/mmap.c:1072 vma_merge+0x428/0x950 mm/mmap.c:1072

I assume this is

		VM_WARN_ON(area && end > area->vm_end);

But lines change around a lot.  It would be great if the script which
generates these reports could quote the code around the indicated file
and line.  Like:

	next = find_vma(mm, prev ? prev->vm_end : 0);
	area = next;
	if (area && area->vm_end == end)		/* cases 6, 7, 8 */
		next = find_vma(mm, next->vm_end);

	/* verify some invariant that must be enforced by the caller */
	VM_WARN_ON(prev && addr <= prev->vm_start);
-->	VM_WARN_ON(area && end > area->vm_end);
	VM_WARN_ON(addr >= end);

	/*
	 * Can it merge with the predecessor?
	 */
	if (prev && prev->vm_end == addr &&




> Modules linked in:
> CPU: 1 PID: 3593 Comm: syz-executor549 Not tainted 5.18.0-rc4-next-20220427-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:vma_merge+0x428/0x950 mm/mmap.c:1072
> Code: 00 e8 5c 1f c4 ff e8 57 1f c4 ff 45 31 f6 e8 4f 1f c4 ff 4c 89 f0 48 83 c4 28 5b 5d 41 5c 41 5d 41 5e 41 5f c3 e8 38 1f c4 ff <0f> 0b e9 6c fd ff ff e8 2c 1f c4 ff 48 8d bd 88 00 00 00 48 b8 00
> RSP: 0018:ffffc90002edfd10 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: 0000000008102073 RCX: 0000000000000000
> RDX: ffff88801d0a3a80 RSI: ffffffff81b62968 RDI: 0000000000000003
> RBP: ffff88807e550bd0 R08: 0000000021001000 R09: 0000000000000000
> R10: ffffffff81b626ce R11: 0000000000000000 R12: 0000555557211000
> R13: 00005555571ef000 R14: ffff88807e550d80 R15: ffff88807e550d80
> FS:  00005555571ef300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005564400b0df0 CR3: 0000000073d7f000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  mlock_fixup+0x349/0x7f0 mm/mlock.c:420
>  apply_mlockall_flags+0x2be/0x440 mm/mlock.c:691
>  __do_sys_mlockall+0x222/0x4b0 mm/mlock.c:719
>  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+0x44/0xae
> RIP: 0033:0x7f9cdd5a1f99
> 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:00007ffecfa63c98 EFLAGS: 00000246 ORIG_RAX: 0000000000000097
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f9cdd5a1f99
> RDX: 00007f9cdd5a1f99 RSI: 0000000000000000 RDI: 0000000000000003
> RBP: 00007f9cdd565f80 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f9cdd566010
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>  </TASK>