[syzbot] [kernel?] general protection fault in vhost_task_start

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6f08c1de13a9 Add linux-next specific files for 20230317
git tree: linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=13d954f6c80000
kernel config: https://syzkaller.appspot.com/x/.config?x=b8cdb12af294ab55
dashboard link: https://syzkaller.appspot.com/bug?extid=6b27b2d2aba1c80cc13b
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=137b6b11c80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16358a16c80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/300a30f8157b/disk-6f08c1de.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7cad5b8b07a2/vmlinux-6f08c1de.xz
kernel image: https://storage.googleapis.com/syzbot-assets/eded56f08b63/bzImage-6f08c1de.xz

The issue was bisected to:

commit 5ab18f4b061ef24a71eea9ffafebd1a82ae2f514
Author: Mike Christie <michael....@oracle.com>
Date: Fri Mar 10 22:03:32 2023 +0000

vhost: use vhost_tasks for worker threads

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=11d88e9ac80000
final oops: https://syzkaller.appspot.com/x/report.txt?x=13d88e9ac80000
console output: https://syzkaller.appspot.com/x/log.txt?x=15d88e9ac80000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6b27b2...@syzkaller.appspotmail.com
Fixes: 5ab18f4b061e ("vhost: use vhost_tasks for worker threads")

RBP: 00007ffe3d8e6050 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004
R13: 431bde82d7b634db R14: 0000000000000000 R15: 0000000000000000
</TASK>
general protection fault, probably for non-canonical address 0xdffffc000000000c: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000060-0x0000000000000067]
CPU: 0 PID: 5103 Comm: syz-executor280 Not tainted 6.3.0-rc2-next-20230317-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
RIP: 0010:vhost_task_start+0x22/0x40 kernel/vhost_task.c:115
Code: 00 00 00 00 00 0f 1f 00 f3 0f 1e fa 53 48 89 fb e8 c3 67 2c 00 48 8d 7b 70 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 0a 48 8b 7b 70 5b e9 fe bd 02 00 e8 79 ec 7e 00 eb
RSP: 0018:ffffc90003a9fc38 EFLAGS: 00010207
RAX: dffffc0000000000 RBX: fffffffffffffff4 RCX: 0000000000000000
RDX: 000000000000000c RSI: ffffffff81564c8d RDI: 0000000000000064
RBP: ffff88802b21dd40 R08: 0000000000000100 R09: ffffffff8c917cf3
R10: 00000000fffffff4 R11: 0000000000000000 R12: fffffffffffffff4
R13: ffff888075d000b0 R14: ffff888075d00000 R15: ffff888075d00008
FS: 0000555556247300(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffe3d8e5ff8 CR3: 00000000215d4000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
vhost_worker_create drivers/vhost/vhost.c:580 [inline]
vhost_dev_set_owner+0x338/0xa90 drivers/vhost/vhost.c:603
vhost_dev_ioctl+0xb4b/0xe70 drivers/vhost/vhost.c:1764
vhost_vsock_dev_ioctl+0x389/0xb30 drivers/vhost/vsock.c:862
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+0x197/0x210 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f82c4252049
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 b1 14 00 00 90 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:00007ffe3d8e6038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007f82c4252049
RDX: 0000000000000000 RSI: 000000000000af01 RDI: 0000000000000003
RBP: 00007ffe3d8e6050 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004
R13: 431bde82d7b634db R14: 0000000000000000 R15: 0000000000000000
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:vhost_task_start+0x22/0x40 kernel/vhost_task.c:115
Code: 00 00 00 00 00 0f 1f 00 f3 0f 1e fa 53 48 89 fb e8 c3 67 2c 00 48 8d 7b 70 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 0a 48 8b 7b 70 5b e9 fe bd 02 00 e8 79 ec 7e 00 eb
RSP: 0018:ffffc90003a9fc38 EFLAGS: 00010207
RAX: dffffc0000000000 RBX: fffffffffffffff4 RCX: 0000000000000000
RDX: 000000000000000c RSI: ffffffff81564c8d RDI: 0000000000000064
RBP: ffff88802b21dd40 R08: 0000000000000100 R09: ffffffff8c917cf3
R10: 00000000fffffff4 R11: 0000000000000000 R12: fffffffffffffff4
R13: ffff888075d000b0 R14: ffff888075d00000 R15: ffff888075d00008
FS: 0000555556247300(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffe3d8e5ff8 CR3: 00000000215d4000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess), 1 bytes skipped:
0: 00 00 add %al,(%rax)
2: 00 00 add %al,(%rax)
4: 0f 1f 00 nopl (%rax)
7: f3 0f 1e fa endbr64
b: 53 push %rbx
c: 48 89 fb mov %rdi,%rbx
f: e8 c3 67 2c 00 callq 0x2c67d7
14: 48 8d 7b 70 lea 0x70(%rbx),%rdi
18: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
1f: fc ff df
22: 48 89 fa mov %rdi,%rdx
25: 48 c1 ea 03 shr $0x3,%rdx
* 29: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1) <-- trapping instruction
2d: 75 0a jne 0x39
2f: 48 8b 7b 70 mov 0x70(%rbx),%rdi
33: 5b pop %rbx
34: e9 fe bd 02 00 jmpq 0x2be37
39: e8 79 ec 7e 00 callq 0x7eecb7
3e: eb .byte 0xeb


---
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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

[Mike Christie]

On 3/21/23 12:03 PM, syzbot wrote:
> RIP: 0010:vhost_task_start+0x22/0x40 kernel/vhost_task.c:115
> Code: 00 00 00 00 00 0f 1f 00 f3 0f 1e fa 53 48 89 fb e8 c3 67 2c 00 48 8d 7b 70 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 0a 48 8b 7b 70 5b e9 fe bd 02 00 e8 79 ec 7e 00 eb
> RSP: 0018:ffffc90003a9fc38 EFLAGS: 00010207
> RAX: dffffc0000000000 RBX: fffffffffffffff4 RCX: 0000000000000000
> RDX: 000000000000000c RSI: ffffffff81564c8d RDI: 0000000000000064
> RBP: ffff88802b21dd40 R08: 0000000000000100 R09: ffffffff8c917cf3
> R10: 00000000fffffff4 R11: 0000000000000000 R12: fffffffffffffff4
> R13: ffff888075d000b0 R14: ffff888075d00000 R15: ffff888075d00008
> FS: 0000555556247300(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007ffe3d8e5ff8 CR3: 00000000215d4000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <TASK>
> vhost_worker_create drivers/vhost/vhost.c:580 [inline]

The return value from vhost_task_create is incorrect if the kzalloc fails.

Christian, here is a fix for what's in your tree. Do you want me to submit
a follow up patch like this or a replacement patch for:

commit 77feab3c4156 ("vhost_task: Allow vhost layer to use copy_process")

with the fix rolled into it?



From 0677ad6d77722f301ca35e8e0f8fd0cbd5ed8484 Mon Sep 17 00:00:00 2001
From: Mike Christie <michael....@oracle.com>
Date: Tue, 21 Mar 2023 12:39:39 -0500
Subject: [PATCH] vhost_task: Fix vhost_task_create return value

vhost_task_create is supposed to return the vhost_task or NULL on
failure. This fixes it to return the correct value when the allocation
of the struct fails.
---
kernel/vhost_task.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/vhost_task.c b/kernel/vhost_task.c
index 4b8aff160640..b7cbd66f889e 100644
--- a/kernel/vhost_task.c
+++ b/kernel/vhost_task.c
@@ -88,7 +88,7 @@ struct vhost_task *vhost_task_create(int (*fn)(void *), void *arg,

vtsk = kzalloc(sizeof(*vtsk), GFP_KERNEL);
if (!vtsk)
- return ERR_PTR(-ENOMEM);
+ return NULL;
init_completion(&vtsk->exited);
vtsk->data = arg;
vtsk->fn = fn;

[Michael S. Tsirkin]

[Michael S. Tsirkin]

Sorry I had nothing to add here. Sent by mistake.

[Christian Brauner]

On Tue, Mar 21, 2023 at 12:46:04PM -0500, Mike Christie wrote:

> On 3/21/23 12:03 PM, syzbot wrote:
> > RIP: 0010:vhost_task_start+0x22/0x40 kernel/vhost_task.c:115
> > Code: 00 00 00 00 00 0f 1f 00 f3 0f 1e fa 53 48 89 fb e8 c3 67 2c 00 48 8d 7b 70 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 0a 48 8b 7b 70 5b e9 fe bd 02 00 e8 79 ec 7e 00 eb
> > RSP: 0018:ffffc90003a9fc38 EFLAGS: 00010207
> > RAX: dffffc0000000000 RBX: fffffffffffffff4 RCX: 0000000000000000
> > RDX: 000000000000000c RSI: ffffffff81564c8d RDI: 0000000000000064
> > RBP: ffff88802b21dd40 R08: 0000000000000100 R09: ffffffff8c917cf3
> > R10: 00000000fffffff4 R11: 0000000000000000 R12: fffffffffffffff4
> > R13: ffff888075d000b0 R14: ffff888075d00000 R15: ffff888075d00008
> > FS: 0000555556247300(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00007ffe3d8e5ff8 CR3: 00000000215d4000 CR4: 00000000003506f0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> > <TASK>
> > vhost_worker_create drivers/vhost/vhost.c:580 [inline]
>
> The return value from vhost_task_create is incorrect if the kzalloc fails.
>
> Christian, here is a fix for what's in your tree. Do you want me to submit
> a follow up patch like this or a replacement patch for:
>
> commit 77feab3c4156 ("vhost_task: Allow vhost layer to use copy_process")

Since this has been in linux-next my tendency is to just put this fix on
top. So please slap a Fixes: tag on it and a Link to the syzbot report.
I also tend to annotate such fixes with "# mainline only":

Fixes: 77feab3c4156 ("vhost_task: Allow vhost layer to use copy_process") # mainline only

to prevent AUTOSEL from picking this up.

Thanks for taking care of this so quickly!
Christian

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.