[PATCH v2] Bluetooth: SCO: fix race conditions in sco_sock_connect()

[PATCH v2] Bluetooth: SCO: fix race conditions in sco_sock_connect()

[Cen Zhang]

sco_sock_connect() checks sk_state and sk_type without holding
the socket lock. Two concurrent connect() syscalls on the same
socket can both pass the check and enter sco_connect(), leading
to use-after-free.

The buggy scenario involves three participants and was confirmed
with additional logging instrumentation:

  Thread A (connect):    HCI disconnect:      Thread B (connect):

  sco_sock_connect(sk)                        sco_sock_connect(sk)
  sk_state==BT_OPEN                           sk_state==BT_OPEN
  (pass, no lock)                             (pass, no lock)
  sco_connect(sk):                            sco_connect(sk):
    hci_dev_lock                                hci_dev_lock
    hci_connect_sco                               <- blocked
      -> hcon1
    sco_conn_add->conn1
    lock_sock(sk)
    sco_chan_add:
      conn1->sk = sk
      sk->conn = conn1
    sk_state=BT_CONNECT
    release_sock
    hci_dev_unlock
                           hci_dev_lock
                           sco_conn_del:
                             lock_sock(sk)
                             sco_chan_del:
                               sk->conn=NULL
                               conn1->sk=NULL
                               sk_state=
                                 BT_CLOSED
                               SOCK_ZAPPED
                             release_sock
                           hci_dev_unlock
                                                  (unblocked)
                                                  hci_connect_sco
                                                    -> hcon2
                                                  sco_conn_add
                                                    -> conn2
                                                  lock_sock(sk)
                                                  sco_chan_add:
                                                    sk->conn=conn2
                                                  sk_state=
                                                    BT_CONNECT
                                                  // zombie sk!
                                                  release_sock
                                                  hci_dev_unlock

Thread B revives a BT_CLOSED + SOCK_ZAPPED socket back to
BT_CONNECT. Subsequent cleanup triggers double sock_put() and
use-after-free. Meanwhile conn1 is leaked as it was orphaned
when sco_conn_del() cleared the association.

Fix this by:
- Moving lock_sock() before the sk_state/sk_type checks in
  sco_sock_connect() to serialize concurrent connect attempts
- Fixing the sk_type != SOCK_SEQPACKET check to actually
  return the error instead of just assigning it
- Adding a state re-check in sco_connect() after lock_sock()
  to catch state changes during the window between the locks
- Adding sco_pi(sk)->conn check in sco_chan_add() to prevent
  double-attach of a socket to multiple connections
- Adding hci_conn_drop() on sco_chan_add failure to prevent
  HCI connection leaks

Fixes: 9a8ec9e8ebb5 ("Bluetooth: SCO: Fix possible circular locking dependency on sco_connect_cfm")
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
---
 net/bluetooth/sco.c | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
index e7db50165879..689788ad26a4 100644
--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c
@@ -298,7 +298,7 @@ static int sco_chan_add(struct sco_conn *conn, struct sock *sk,
 	int err = 0;
 
 	sco_conn_lock(conn);
-	if (conn->sk)
+	if (conn->sk || sco_pi(sk)->conn)
 		err = -EBUSY;
 	else
 		__sco_chan_add(conn, sk, parent);
@@ -353,9 +353,20 @@ static int sco_connect(struct sock *sk)
 
 	lock_sock(sk);
 
+	/* Recheck state after reacquiring the socket lock, as another
+	 * thread may have changed it (e.g., closed the socket).
+	 */
+	if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND) {
+		release_sock(sk);
+		hci_conn_drop(hcon);
+		err = -EBADFD;
+		goto unlock;
+	}
+
 	err = sco_chan_add(conn, sk, NULL);
 	if (err) {
 		release_sock(sk);
+		hci_conn_drop(hcon);
 		goto unlock;
 	}
 
@@ -652,13 +663,18 @@ static int sco_sock_connect(struct socket *sock, struct sockaddr_unsized *addr,
 	    addr->sa_family != AF_BLUETOOTH)
 		return -EINVAL;
 
-	if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND)
+	lock_sock(sk);
+
+	if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND) {
+		release_sock(sk);
 		return -EBADFD;
+	}
 
-	if (sk->sk_type != SOCK_SEQPACKET)
-		err = -EINVAL;
+	if (sk->sk_type != SOCK_SEQPACKET) {
+		release_sock(sk);
+		return -EINVAL;
+	}
 
-	lock_sock(sk);
 	/* Set destination address and psm */
 	bacpy(&sco_pi(sk)->dst, &sa->sco_bdaddr);
 	release_sock(sk);
-- 
2.34.1

RE: [v2] Bluetooth: SCO: fix race conditions in sco_sock_connect()

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 2833 bytes --]

This is automated email and please do not reply to this email!

Dear submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
This is a CI test results with your patch series:
PW Link:https://patchwork.kernel.org/project/bluetooth/list/?series=1073049

---Test result---

Test Summary:
CheckPatch                    PENDING   0.50 seconds
GitLint                       PENDING   0.35 seconds
SubjectPrefix                 PASS      0.10 seconds
BuildKernel                   PASS      25.90 seconds
CheckAllWarning               PASS      28.54 seconds
CheckSparse                   PASS      28.59 seconds
BuildKernel32                 PASS      25.67 seconds
TestRunnerSetup               PASS      545.42 seconds
TestRunner_l2cap-tester       PASS      28.51 seconds
TestRunner_iso-tester         FAIL      37.06 seconds
TestRunner_bnep-tester        PASS      6.68 seconds
TestRunner_mgmt-tester        FAIL      115.86 seconds
TestRunner_rfcomm-tester      PASS      9.65 seconds
TestRunner_sco-tester         FAIL      14.58 seconds
TestRunner_ioctl-tester       PASS      10.40 seconds
TestRunner_mesh-tester        FAIL      11.80 seconds
TestRunner_smp-tester         PASS      8.77 seconds
TestRunner_userchan-tester    PASS      6.76 seconds
IncrementalBuild              PENDING   0.55 seconds

Details
##############################
Test: CheckPatch - PENDING
Desc: Run checkpatch.pl script
Output:

##############################
Test: GitLint - PENDING
Desc: Run gitlint
Output:

##############################
Test: TestRunner_iso-tester - FAIL
Desc: Run iso-tester with test-runner
Output:
BUG: KASAN: slab-use-after-free in le_read_features_complete+0x7e/0x2b0
Total: 141, Passed: 141 (100.0%), Failed: 0, Not Run: 0
##############################
Test: TestRunner_mgmt-tester - FAIL
Desc: Run mgmt-tester with test-runner
Output:
Total: 494, Passed: 489 (99.0%), Failed: 1, Not Run: 4

Failed Test Cases
Read Exp Feature - Success                           Failed       0.105 seconds
##############################
Test: TestRunner_sco-tester - FAIL
Desc: Run sco-tester with test-runner
Output:
WARNING: possible circular locking dependency detected
BUG: sleeping function called from invalid context at net/core/sock.c:3782
Total: 30, Passed: 30 (100.0%), Failed: 0, Not Run: 0
##############################
Test: TestRunner_mesh-tester - FAIL
Desc: Run mesh-tester with test-runner
Output:
Total: 10, Passed: 8 (80.0%), Failed: 2, Not Run: 0

Failed Test Cases
Mesh - Send cancel - 1                               Timed out    1.904 seconds
Mesh - Send cancel - 2                               Timed out    1.992 seconds
##############################
Test: IncrementalBuild - PENDING
Desc: Incremental build with the patches in the series
Output:



---
Regards,
Linux Bluetooth

Re: [PATCH v2] Bluetooth: SCO: fix race conditions in sco_sock_connect()

[patchwork-bot+bluetooth]

Hello:

This patch was applied to bluetooth/bluetooth-next.git (master)
by Luiz Augusto von Dentz <luiz.von.dentz@intel.com>:

On Thu, 26 Mar 2026 23:16:45 +0800 you wrote:
> sco_sock_connect() checks sk_state and sk_type without holding
> the socket lock. Two concurrent connect() syscalls on the same
> socket can both pass the check and enter sco_connect(), leading
> to use-after-free.
> 
> The buggy scenario involves three participants and was confirmed
> with additional logging instrumentation:
> 
> [...]

Here is the summary with links:
  - [v2] Bluetooth: SCO: fix race conditions in sco_sock_connect()
    https://git.kernel.org/bluetooth/bluetooth-next/c/401702ac8a51

You are awesome, thank you!
-- 
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