[PATCH] Bluetooth: fix UAF read of ->accept_q in bt_accept_poll()

[Jann Horn <jannh@google.com>]

Use lock_sock() to guard against bt_accept_poll() racing with concurrent
close(accept()), which can lead to UAF:

task 1           task 2
======           ======
                 __x64_sys_poll
                   __se_sys_poll
                     __do_sys_poll
                       do_sys_poll
                         do_poll
                           do_pollfd
                             vfs_poll
                               sock_poll
                                 bt_sock_poll
                                   bt_accept_poll
                                     [read ->accept_q next pointer]
__x64_sys_accept
  __se_sys_accept
    __do_sys_accept
      __sys_accept4
        __sys_accept4_file
          do_accept
            l2cap_sock_accept
              bt_accept_dequeue
                bt_accept_unlink
                  [removes new socket from ->accept_q]
__x64_sys_close
  __se_sys_close
    __do_sys_close
      fput_close_sync
        __fput
          sock_close
            __sock_release
              l2cap_sock_release
                l2cap_sock_kill
                  sock_put
                    sk_free
                      __sk_free
                        sk_destruct
                          __sk_destruct
                            [frees new socket]
                                     [UAF read of ->sk_state]

This UAF only leads to incorrect reads, it does not corrupt memory; it is a
fairly tight race window; I believe every race attempt requires an
incoming bluetooth connection; and the leaked data is limited.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
---
 net/bluetooth/af_bluetooth.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/af_bluetooth.c b/net/bluetooth/af_bluetooth.c
index 33d053d63407..d24897167838 100644
--- a/net/bluetooth/af_bluetooth.c
+++ b/net/bluetooth/af_bluetooth.c
@@ -521,13 +521,17 @@ static inline __poll_t bt_accept_poll(struct sock *parent)
 	struct bt_sock *s, *n;
 	struct sock *sk;
 
+	lock_sock(parent);
 	list_for_each_entry_safe(s, n, &bt_sk(parent)->accept_q, accept_q) {
 		sk = (struct sock *)s;
 		if (sk->sk_state == BT_CONNECTED ||
 		    (test_bit(BT_SK_DEFER_SETUP, &bt_sk(parent)->flags) &&
-		     sk->sk_state == BT_CONNECT2))
+		     sk->sk_state == BT_CONNECT2)) {
+			release_sock(parent);
 			return EPOLLIN | EPOLLRDNORM;
+		}
 	}
+	release_sock(parent);
 
 	return 0;
 }

---
base-commit: 6d35786de28116ecf78797a62b84e6bf3c45aa5a
change-id: 20260504-bluetooth-accept-uaf-fix-df393cbda114

--  
Jann Horn <jannh@google.com>