vsock: Orphan socket after transport release

jira VULN-53604
cve CVE-2025-21756
commit-author Michal Luczaj <mhal@rbox.co>
commit 78dafe1
upstream-diff Indentation is different from upstream change because
              this kernel lacks 135ffc7 ("bpf, vsock: Invoke
              proto::close on close()").  Otherwise the change
              content is the same.

During socket release, sock_orphan() is called without considering that it
sets sk->sk_wq to NULL. Later, if SO_LINGER is enabled, this leads to a
null pointer dereferenced in virtio_transport_wait_close().

Orphan the socket only after transport release.

Partially reverts the 'Fixes:' commit.

KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
 lock_acquire+0x19e/0x500
 _raw_spin_lock_irqsave+0x47/0x70
 add_wait_queue+0x46/0x230
 virtio_transport_release+0x4e7/0x7f0
 __vsock_release+0xfd/0x490
 vsock_release+0x90/0x120
 __sock_release+0xa3/0x250
 sock_close+0x14/0x20
 __fput+0x35e/0xa90
 __x64_sys_close+0x78/0xd0
 do_syscall_64+0x93/0x1b0
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

	Reported-by: syzbot+9d55b199192a4be7d02c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9d55b199192a4be7d02c
Fixes: fcdd224 ("vsock: Keep the binding until socket destruction")
	Tested-by: Luigi Leonardi <leonardi@redhat.com>
	Reviewed-by: Luigi Leonardi <leonardi@redhat.com>
	Signed-off-by: Michal Luczaj <mhal@rbox.co>
Link: https://patch.msgid.link/20250210-vsock-linger-nullderef-v3-1-ef6244d02b54@rbox.co
	Signed-off-by: Jakub Kicinski <kuba@kernel.org>
(cherry picked from commit 78dafe1)
	Signed-off-by: Brett Mastbergen <bmastbergen@ciq.com>

Author: bmastbergen

net/vmw_vsock/af_vsock.c

@@ -792,13 +792,19 @@ static void __vsock_release(struct sock *sk, int level)
 		 */
 		lock_sock_nested(sk, level);
 
-		sock_orphan(sk);
+		/* Indicate to vsock_remove_sock() that the socket is being released and
+		 * can be removed from the bound_table. Unlike transport reassignment
+		 * case, where the socket must remain bound despite vsock_remove_sock()
+		 * being called from the transport release() callback.
+		 */
+		sock_set_flag(sk, SOCK_DEAD);
 
 		if (vsk->transport)
 			vsk->transport->release(vsk);
 		else if (sk->sk_type == SOCK_STREAM)
 			vsock_remove_sock(vsk);
 
+		sock_orphan(sk);
 		sk->sk_shutdown = SHUTDOWN_MASK;
 
 		skb_queue_purge(&sk->sk_receive_queue);