Re: [syzbot] [kvm?] [net?] [virt?] general protection fault in virtio_transport_purge_skbs

Stefano Garzarella
2023-03-24T08:56:40Z

On Fri, Mar 24, 2023 at 9:31 AM Stefano Garzarella <sgarzare@redhat.com> wrote:
>
> Hi Bobby,
> can you take a look at this report?
>
> It seems related to the changes we made to support skbuff.

Could it be a problem of concurrent access to pkt_queue ?

IIUC we should hold pkt_queue.lock when we call skb_queue_splice_init()
and remove pkt_list_lock. (or hold pkt_list_lock when calling
virtio_transport_purge_skbs, but pkt_list_lock seems useless now that
we use skbuff)

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git fff5a5e7f528

--- a/net/vmw_vsock/vsock_loopback.c
+++ b/net/vmw_vsock/vsock_loopback.c
@@ -15,7 +15,6 @@
struct vsock_loopback {
struct workqueue_struct *workqueue;

- spinlock_t pkt_list_lock; /* protects pkt_list */
struct sk_buff_head pkt_queue;
struct work_struct pkt_work;
};
@@ -32,9 +31,7 @@ static int vsock_loopback_send_pkt(struct sk_buff *skb)
struct vsock_loopback *vsock = &the_vsock_loopback;
int len = skb->len;

- spin_lock_bh(&vsock->pkt_list_lock);
skb_queue_tail(&vsock->pkt_queue, skb);
- spin_unlock_bh(&vsock->pkt_list_lock);

queue_work(vsock->workqueue, &vsock->pkt_work);

@@ -113,9 +110,9 @@ static void vsock_loopback_work(struct work_struct *work)

skb_queue_head_init(&pkts);

- spin_lock_bh(&vsock->pkt_list_lock);
+ spin_lock_bh(&vsock->pkt_queue.lock);
skb_queue_splice_init(&vsock->pkt_queue, &pkts);
- spin_unlock_bh(&vsock->pkt_list_lock);
+ spin_unlock_bh(&vsock->pkt_queue.lock);

while ((skb = __skb_dequeue(&pkts))) {
virtio_transport_deliver_tap_pkt(skb);
@@ -132,7 +129,6 @@ static int __init vsock_loopback_init(void)
if (!vsock->workqueue)
return -ENOMEM;

- spin_lock_init(&vsock->pkt_list_lock);
skb_queue_head_init(&vsock->pkt_queue);
INIT_WORK(&vsock->pkt_work, vsock_loopback_work);

>
> Thanks,
> Stefano
>
> On Fri, Mar 24, 2023 at 1:52 AM syzbot
> <syzbot+befff0a9536049e7902e@syzkaller.appspotmail.com> wrote:
> >
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit: fff5a5e7f528 Merge tag 'for-linus' of git://git.armlinux.o..
> > git tree: upstream
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=1136e97ac80000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=aaa4b45720ca0519
> > dashboard link: https://syzkaller.appspot.com/bug?extid=befff0a9536049e7902e
> > 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=14365781c80000
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12eebc66c80000
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/997791f5f9e1/disk-fff5a5e7.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/0b0155b5eac1/vmlinux-fff5a5e7.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/8d98dd2ba6b6/bzImage-fff5a5e7.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+befff0a9536049e7902e@syzkaller.appspotmail.com
> >
> > general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
> > KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> > CPU: 0 PID: 8759 Comm: syz-executor379 Not tainted 6.3.0-rc3-syzkaller-00026-gfff5a5e7f528 #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
> > RIP: 0010:virtio_transport_purge_skbs+0x139/0x4c0 net/vmw_vsock/virtio_transport_common.c:1370
> > Code: 00 00 00 00 fc ff df 48 89 c2 48 89 44 24 28 48 c1 ea 03 48 8d 04 1a 48 89 44 24 10 eb 29 e8 ee 27 a3 f7 48 89 e8 48 c1 e8 03 <80> 3c 18 00 0f 85 a6 02 00 00 49 39 ec 48 8b 55 00 49 89 ef 0f 84
> > RSP: 0018:ffffc90006427b48 EFLAGS: 00010256
> > RAX: 0000000000000000 RBX: dffffc0000000000 RCX: 0000000000000000
> > RDX: ffff8880211157c0 RSI: ffffffff89dfbd12 RDI: ffff88802c11a018
> > RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000003
> > R10: fffff52000c84f5b R11: 0000000000000000 R12: ffffffff92179188
> > R13: ffffc90006427ba0 R14: ffff88801e0f1100 R15: ffff88802c11a000
> > FS: 00007f01fdd51700(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00007f01fdd30718 CR3: 000000002a3f9000 CR4: 0000000000350ef0
> > Call Trace:
> > <TASK>
> > vsock_loopback_cancel_pkt+0x1c/0x20 net/vmw_vsock/vsock_loopback.c:48
> > vsock_transport_cancel_pkt net/vmw_vsock/af_vsock.c:1284 [inline]
> > vsock_connect+0x852/0xcc0 net/vmw_vsock/af_vsock.c:1426
> > __sys_connect_file+0x153/0x1a0 net/socket.c:2001
> > __sys_connect+0x165/0x1a0 net/socket.c:2018
> > __do_sys_connect net/socket.c:2028 [inline]
> > __se_sys_connect net/socket.c:2025 [inline]
> > __x64_sys_connect+0x73/0xb0 net/socket.c:2025
> > 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: 0033:0x7f01fdda0159
> > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 41 15 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 b8 ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007f01fdd51308 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
> > RAX: ffffffffffffffda RBX: 00007f01fde28428 RCX: 00007f01fdda0159
> > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
> > RBP: 00007f01fde28420 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 00007f01fddf606c
> > R13: 0000000000000000 R14: 00007f01fdd51400 R15: 0000000000022000
> > </TASK>
> > Modules linked in:
> > ---[ end trace 0000000000000000 ]---
> > RIP: 0010:virtio_transport_purge_skbs+0x139/0x4c0 net/vmw_vsock/virtio_transport_common.c:1370
> > Code: 00 00 00 00 fc ff df 48 89 c2 48 89 44 24 28 48 c1 ea 03 48 8d 04 1a 48 89 44 24 10 eb 29 e8 ee 27 a3 f7 48 89 e8 48 c1 e8 03 <80> 3c 18 00 0f 85 a6 02 00 00 49 39 ec 48 8b 55 00 49 89 ef 0f 84
> > RSP: 0018:ffffc90006427b48 EFLAGS: 00010256
> > RAX: 0000000000000000 RBX: dffffc0000000000 RCX: 0000000000000000
> > RDX: ffff8880211157c0 RSI: ffffffff89dfbd12 RDI: ffff88802c11a018
> > RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000003
> > R10: fffff52000c84f5b R11: 0000000000000000 R12: ffffffff92179188
> > R13: ffffc90006427ba0 R14: ffff88801e0f1100 R15: ffff88802c11a000
> > FS: 00007f01fdd51700(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00007f01fdd30718 CR3: 000000002a3f9000 CR4: 0000000000350ef0
> > ----------------
> > Code disassembly (best guess), 6 bytes skipped:
> > 0: df 48 89 fisttps -0x77(%rax)
> > 3: c2 48 89 retq $0x8948
> > 6: 44 24 28 rex.R and $0x28,%al
> > 9: 48 c1 ea 03 shr $0x3,%rdx
> > d: 48 8d 04 1a lea (%rdx,%rbx,1),%rax
> > 11: 48 89 44 24 10 mov %rax,0x10(%rsp)
> > 16: eb 29 jmp 0x41
> > 18: e8 ee 27 a3 f7 callq 0xf7a3280b
> > 1d: 48 89 e8 mov %rbp,%rax
> > 20: 48 c1 e8 03 shr $0x3,%rax
> > * 24: 80 3c 18 00 cmpb $0x0,(%rax,%rbx,1) <-- trapping instruction
> > 28: 0f 85 a6 02 00 00 jne 0x2d4
> > 2e: 49 39 ec cmp %rbp,%r12
> > 31: 48 8b 55 00 mov 0x0(%rbp),%rdx
> > 35: 49 89 ef mov %rbp,%r15
> > 38: 0f .byte 0xf
> > 39: 84 .byte 0x84
> >
> >
> > ---
> > 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@googlegroups.com.
> >
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > syzbot can test patches for this issue, for details see:
> > https://goo.gl/tpsmEJ#testing-patches
> >