Hi Michal,
On Mon, Oct 20, 2025 at 05:02:56PM -0700, syzbot wrote:
Hello,
syzbot found the following issue on:
HEAD commit: d9043c79ba68 Merge tag 'sched_urgent_for_v6.18_rc2' of git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=130983cd980000
kernel config: https://syzkaller.appspot.com/x/.config?x=f3e7b5a3627a90dd
dashboard link: https://syzkaller.appspot.com/bug?extid=10e35716f8e4929681fa
compiler: gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for
Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17f0f52f980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11ea9734580000
Downloadable assets:
disk image (non-bootable):
https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-d9043c79.raw.xz
vmlinux:
https://storage.googleapis.com/syzbot-assets/0546b6eaf1aa/vmlinux-d9043c79.xz
kernel image:
https://storage.googleapis.com/syzbot-assets/81285b4ada51/bzImage-d9043c79.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/6098 is trying to acquire lock:
ffff8880363b8258 (sk_lock-AF_VSOCK){+.+.}-{0:0}, at: lock_sock
include/net/sock.h:1679 [inline]
ffff8880363b8258 (sk_lock-AF_VSOCK){+.+.}-{0:0}, at: vsock_linger+0x25e/0x4d0
net/vmw_vsock/af_vsock.c:1066
Could this be related to our recent work on linger in vsock?
but task is already holding lock:
ffffffff906260a8 (vsock_register_mutex){+.+.}-{4:4}, at:
vsock_assign_transport+0xf2/0x900 net/vmw_vsock/af_vsock.c:469
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (vsock_register_mutex){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:598 [inline]
__mutex_lock+0x193/0x1060 kernel/locking/mutex.c:760
vsock_registered_transport_cid net/vmw_vsock/af_vsock.c:560 [inline]
Ah, no maybe this is related to commit 209fd720838a ("vsock:
Fix transport_{g2h,h2g} TOCTOU") where we added locking in
vsock_find_cid().
Maybe we can just move the checks on top of __vsock_bind() to the
caller. I mean:
/* First ensure this socket isn't already bound. */
if (vsock_addr_bound(&vsk->local_addr))
return -EINVAL;
/* Now bind to the provided address or select appropriate values if
* none are provided (VMADDR_CID_ANY and VMADDR_PORT_ANY). Note that
* like AF_INET prevents binding to a non-local IP address (in most
* cases), we only allow binding to a local CID.
*/
if (addr->svm_cid != VMADDR_CID_ANY && !vsock_find_cid(addr->svm_cid))
return -EADDRNOTAVAIL;
We have 2 callers: vsock_auto_bind() and vsock_bind().
vsock_auto_bind() is already checking if the socket is already bound,
if not is setting VMADDR_CID_ANY, so we can skip those checks.
In vsock_bind() we can do the checks before lock_sock(sk), at least the
checks on vm_addr, calling vsock_find_cid().
I'm preparing a patch to do this.
Stefano
vsock_find_cid net/vmw_vsock/af_vsock.c:570 [inline]
__vsock_bind+0x1b5/0xa10 net/vmw_vsock/af_vsock.c:752
vsock_bind+0xc6/0x120 net/vmw_vsock/af_vsock.c:1002
__sys_bind_socket net/socket.c:1874 [inline]
__sys_bind_socket net/socket.c:1866 [inline]
__sys_bind+0x1a7/0x260 net/socket.c:1905
__do_sys_bind net/socket.c:1910 [inline]
__se_sys_bind net/socket.c:1908 [inline]
__x64_sys_bind+0x72/0xb0 net/socket.c:1908
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #0 (sk_lock-AF_VSOCK){+.+.}-{0:0}:
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x126f/0x1c90 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
lock_sock_nested+0x41/0xf0 net/core/sock.c:3720
lock_sock include/net/sock.h:1679 [inline]
vsock_linger+0x25e/0x4d0 net/vmw_vsock/af_vsock.c:1066
virtio_transport_close net/vmw_vsock/virtio_transport_common.c:1271
[inline]
virtio_transport_release+0x52a/0x640
net/vmw_vsock/virtio_transport_common.c:1291
vsock_assign_transport+0x320/0x900 net/vmw_vsock/af_vsock.c:502
vsock_connect+0x201/0xee0 net/vmw_vsock/af_vsock.c:1578
__sys_connect_file+0x141/0x1a0 net/socket.c:2102
__sys_connect+0x13b/0x160 net/socket.c:2121
__do_sys_connect net/socket.c:2127 [inline]
__se_sys_connect net/socket.c:2124 [inline]
__x64_sys_connect+0x72/0xb0 net/socket.c:2124
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(vsock_register_mutex);
lock(sk_lock-AF_VSOCK);
lock(vsock_register_mutex);
lock(sk_lock-AF_VSOCK);
*** DEADLOCK ***
1 lock held by syz.0.17/6098:
#0: ffffffff906260a8 (vsock_register_mutex){+.+.}-{4:4}, at:
vsock_assign_transport+0xf2/0x900 net/vmw_vsock/af_vsock.c:469
stack backtrace:
CPU: 3 UID: 0 PID: 6098 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
print_circular_bug+0x275/0x350 kernel/locking/lockdep.c:2043
check_noncircular+0x14c/0x170 kernel/locking/lockdep.c:2175
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x126f/0x1c90 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
lock_sock_nested+0x41/0xf0 net/core/sock.c:3720
lock_sock include/net/sock.h:1679 [inline]
vsock_linger+0x25e/0x4d0 net/vmw_vsock/af_vsock.c:1066
virtio_transport_close net/vmw_vsock/virtio_transport_common.c:1271 [inline]
virtio_transport_release+0x52a/0x640
net/vmw_vsock/virtio_transport_common.c:1291
vsock_assign_transport+0x320/0x900 net/vmw_vsock/af_vsock.c:502
vsock_connect+0x201/0xee0 net/vmw_vsock/af_vsock.c:1578
__sys_connect_file+0x141/0x1a0 net/socket.c:2102
__sys_connect+0x13b/0x160 net/socket.c:2121
__do_sys_connect net/socket.c:2127 [inline]
__se_sys_connect net/socket.c:2124 [inline]
__x64_sys_connect+0x72/0xb0 net/socket.c:2124
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f767bf8efc9
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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff0a2857b8 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007f767c1e5fa0 RCX: 00007f767bf8efc9
RDX: 0000000000000010 RSI: 0000200000000000 RDI: 0000000000000004
RBP: 00007f767c011f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f767c1e5fa0 R14: 00007f767c1e5fa0 R15: 0000000000000003
</TASK>
---
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