[syzbot] [virt?] [net?] possible deadlock in vsock_linger

[syzbot]

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: syzbot+10e357...@syzkaller.appspotmail.com

======================================================
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

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]
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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If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

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#syz test: git://repo/address.git branch-or-commit-hash
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#syz undup

[Stefano Garzarella]

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: syzbot+10e357...@syzkaller.appspotmail.com
>
>======================================================
>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

[Stefano Garzarella]

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

#syz test

--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -565,6 +565,11 @@ static u32 vsock_registered_transport_cid(const struct vsock_transport **transpo
return cid;
}

+/* vsock_find_cid() must be called outside lock_sock/release_sock
+ * section to avoid a potential lock inversion deadlock with
+ * vsock_assign_transport() where `vsock_register_mutex` is taken when
+ * `sk_lock-AF_VSOCK` is already held.
+ */
bool vsock_find_cid(unsigned int cid)
{
if (cid == vsock_registered_transport_cid(&transport_g2h))
@@ -735,23 +740,14 @@ static int __vsock_bind_dgram(struct vsock_sock *vsk,
return vsk->transport->dgram_bind(vsk, addr);
}

+/* The caller must ensure the socket is not already bound and provide a valid
+ * `addr` to bind (VMADDR_CID_ANY, or a CID assgined to a transport).
+ */
static int __vsock_bind(struct sock *sk, struct sockaddr_vm *addr)
{
struct vsock_sock *vsk = vsock_sk(sk);
int retval;

- /* 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;
-
switch (sk->sk_socket->type) {
case SOCK_STREAM:
case SOCK_SEQPACKET:
@@ -991,15 +987,33 @@ vsock_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
{
int err;
struct sock *sk;
+ struct vsock_sock *vsk;
struct sockaddr_vm *vm_addr;

sk = sock->sk;
+ vsk = vsock_sk(sk);

if (vsock_addr_cast(addr, addr_len, &vm_addr) != 0)
return -EINVAL;

+ /* Like AF_INET prevents binding to a non-local IP address (in most
+ * cases), we only allow binding to a local CID.
+ */
+ if (vm_addr->svm_cid != VMADDR_CID_ANY &&
+ !vsock_find_cid(vm_addr->svm_cid))
+ return -EADDRNOTAVAIL;
+
lock_sock(sk);
+
+ /* Ensure this socket isn't already bound. */
+ if (vsock_addr_bound(&vsk->local_addr)) {
+ err = -EINVAL;
+ goto out;
+ }
+
err = __vsock_bind(sk, vm_addr);
+
+out:
release_sock(sk);

return err;

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

failed to apply patch:
checking file net/vmw_vsock/af_vsock.c
patch: **** unexpected end of file in patch



Tested on:

commit: 6548d364 Merge tag 'cgroup-for-6.18-rc2-fixes' of git:..
git tree: upstream

kernel config: https://syzkaller.appspot.com/x/.config?x=f3e7b5a3627a90dd
dashboard link: https://syzkaller.appspot.com/bug?extid=10e35716f8e4929681fa
compiler:

patch: https://syzkaller.appspot.com/x/patch.diff?x=17204e7c580000

[Stefano Garzarella]

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

#syz test

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in vsock_linger

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------

syz.0.17/6384 is trying to acquire lock:
ffff888055028b18 (sk_lock-AF_VSOCK){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1679 [inline]
ffff888055028b18 (sk_lock-AF_VSOCK){+.+.}-{0:0}, at: vsock_linger+0x25e/0x4d0 net/vmw_vsock/af_vsock.c:1080

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_assign_transport+0xf2/0x900 net/vmw_vsock/af_vsock.c:469
vsock_connect+0x201/0xee0 net/vmw_vsock/af_vsock.c:1592

__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

-> #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:1080

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:1592

__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.0.17/6384:

#0: ffffffff906260a8 (vsock_register_mutex){+.+.}-{4:4}, at: vsock_assign_transport+0xf2/0x900 net/vmw_vsock/af_vsock.c:469

stack backtrace:

CPU: 1 UID: 0 PID: 6384 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:1080

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:1592

__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: 0033:0x7f300598efc9

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:00007f3006912038 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007f3005be5fa0 RCX: 00007f300598efc9

RDX: 0000000000000010 RSI: 0000200000000000 RDI: 0000000000000004

RBP: 00007f3005a11f91 R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000

R13: 00007f3005be6038 R14: 00007f3005be5fa0 R15: 00007ffdba0a0048
</TASK>

Tested on:

commit: 6548d364 Merge tag 'cgroup-for-6.18-rc2-fixes' of git:..

git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=162a5492580000

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

patch: https://syzkaller.appspot.com/x/patch.diff?x=17a04e7c580000

[Stefano Garzarella]

mmm, no, this is more related to vsock_linger() where sk_wait_event()
releases and locks again the sk_lock.
So, it should be related to commit 687aa0c5581b ("vsock: Fix
transport_* TOCTOU") where we take vsock_register_mutex in
vsock_assign_transport() while calling vsk->transport->release().

So, maybe we need to move the release and vsock_deassign_transport()
after unlocking vsock_register_mutex.

Stefano

[Stefano Garzarella]

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

#syz test

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+10e357...@syzkaller.appspotmail.com
Tested-by: syzbot+10e357...@syzkaller.appspotmail.com

Tested on:

commit: 6548d364 Merge tag 'cgroup-for-6.18-rc2-fixes' of git:..

git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1534c3cd980000

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

patch: https://syzkaller.appspot.com/x/patch.diff?x=11a90d2f980000

Note: testing is done by a robot and is best-effort only.

[Stefano Garzarella]

I implemented this here:
https://lore.kernel.org/netdev/20251021121718.1...@redhat.com/

sysbot successfully tested it.

Stefano