[PATCH v3] Bluetooth: af_bluetooth: Fix double list_del and UAF in accept_q

[PATCH v3] Bluetooth: af_bluetooth: Fix double list_del and UAF in accept_q

[Nguyen Ngoc Thang]

bt_sk(sk)->parent is a raw pointer with no refcount backing it, so a
child sitting in the listening socket's accept_q can outlive it. When
the child's channel is torn down independently (e.g. hci_error_reset()
-> l2cap_conn_del() -> l2cap_sock_teardown_cb()), bt_accept_unlink()
dereferences the freed parent, corrupting its accept_q_lock and list.

Additionally, if multiple threads concurrently tear down the child
socket, bt_accept_unlink() can be called multiple times. Without
checking if the socket is still in the list, the second thread will
perform a double list_del_init(), causing list_del corruption (kernel BUG).

Fix this by:
1. Taking a reference on parent in bt_accept_enqueue() and dropping it
   only when actually unlinked in bt_accept_unlink().
2. Checking !list_empty(&bt_sk(sk)->accept_q) inside the accept_q_lock
   to prevent double unlinking.
3. Moving sock_put() outside of the spinlock to avoid sleeping in an
   atomic context.

Reported-by: syzbot+534002670dd34a114fdc@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=534002670dd34a114fdc
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")

Signed-off-by: Nguyen Ngoc Thang <ngocthang2710.1999@gmail.com>
---
 net/bluetooth/af_bluetooth.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/net/bluetooth/af_bluetooth.c b/net/bluetooth/af_bluetooth.c
index 411d66f24393..7797b1052808 100644
--- a/net/bluetooth/af_bluetooth.c
+++ b/net/bluetooth/af_bluetooth.c
@@ -224,6 +224,10 @@ void bt_accept_enqueue(struct sock *parent, struct sock *sk, bool bh)
 	else
 		lock_sock_nested(sk, SINGLE_DEPTH_NESTING);
 
+	/* Hold a reference on parent so it cannot be freed while sk keeps
+	 * a raw pointer to it via bt_sk(sk)->parent.
+	 */
+	sock_hold(parent);
 	bt_sk(sk)->parent = parent;
 
 	spin_lock_bh(&par->accept_q_lock);
@@ -257,15 +261,24 @@ EXPORT_SYMBOL(bt_accept_enqueue);
 void bt_accept_unlink(struct sock *sk)
 {
 	struct sock *parent = bt_sk(sk)->parent;
+	bool unlinked = false;
 
-	BT_DBG("sk %p state %d", sk, sk->sk_state);
+	if (!parent)
+		return;
 
 	spin_lock_bh(&bt_sk(parent)->accept_q_lock);
-	list_del_init(&bt_sk(sk)->accept_q);
-	sk_acceptq_removed(parent);
+	if (!list_empty(&bt_sk(sk)->accept_q)) {
+		list_del_init(&bt_sk(sk)->accept_q);
+		sk_acceptq_removed(parent);
+		unlinked = true;
+	}
 	spin_unlock_bh(&bt_sk(parent)->accept_q_lock);
-	bt_sk(sk)->parent = NULL;
-	sock_put(sk);
+
+	if (unlinked) {
+		bt_sk(sk)->parent = NULL;
+		sock_put(parent);
+		sock_put(sk);
+	}
 }
 EXPORT_SYMBOL(bt_accept_unlink);
 
-- 
2.43.0

RE: [v3] Bluetooth: af_bluetooth: Fix double list_del and UAF in accept_q

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 2227 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/series/1168560/

---Test result---

Test Summary:
CheckPatch                    PASS      0.60 seconds
VerifyFixes                   PASS      0.10 seconds
VerifySignedoff               PASS      0.10 seconds
GitLint                       PASS      0.29 seconds
SubjectPrefix                 PASS      0.09 seconds
BuildKernel                   PASS      29.00 seconds
CheckAllWarning               PASS      31.93 seconds
CheckSparse                   PASS      34.15 seconds
BuildKernel32                 PASS      27.88 seconds
CheckKernelLLVM               PASS      31.52 seconds
TestRunnerSetup               PASS      704.03 seconds
TestRunner_l2cap-tester       PASS      16.11 seconds
TestRunner_iso-tester         PASS      36.46 seconds
TestRunner_bnep-tester        PASS      3.76 seconds
TestRunner_mgmt-tester        FAIL      60.00 seconds
TestRunner_rfcomm-tester      PASS      4.17 seconds
TestRunner_sco-tester         PASS      11.49 seconds
TestRunner_ioctl-tester       PASS      5.29 seconds
TestRunner_mesh-tester        FAIL      8.91 seconds
TestRunner_smp-tester         PASS      4.07 seconds
TestRunner_userchan-tester    PASS      2.94 seconds
TestRunner_6lowpan-tester     PASS      4.13 seconds
IncrementalBuild              PASS      30.91 seconds

Details
##############################
Test: TestRunner_mgmt-tester - FAIL
Desc: Run mgmt-tester with test-runner
Output:
Total: 501, Passed: 496 (99.0%), Failed: 1, Not Run: 4

Failed Test Cases
Read Exp Feature - Success                           Failed       0.022 seconds
##############################
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    2.523 seconds
Mesh - Send cancel - 2                               Timed out    1.997 seconds


https://github.com/bluez/bluetooth-next/pull/790

---
Regards,
Linux Bluetooth

Re: [PATCH v3] Bluetooth: af_bluetooth: Fix double list_del and UAF in accept_q

[Pauli Virtanen]

Hi,

pe, 2026-09-18 kello 17:47 +0700, Nguyen Ngoc Thang kirjoitti:
> bt_sk(sk)->parent is a raw pointer with no refcount backing it, so a
> child sitting in the listening socket's accept_q can outlive it. When
> the child's channel is torn down independently (e.g. hci_error_reset()
> -> l2cap_conn_del() -> l2cap_sock_teardown_cb()), bt_accept_unlink()
> dereferences the freed parent, corrupting its accept_q_lock and list.

This was resent without replying to previous comments:

https://lore.kernel.org/linux-bluetooth/1baff112d1ebd255575c7e52936b13db10f218b7.camel@iki.fi/

AFAIK the issue is already fixed upstream in a different way.

> Additionally, if multiple threads concurrently tear down the child
> socket, bt_accept_unlink() can be called multiple times. Without
> checking if the socket is still in the list, the second thread will
> perform a double list_del_init(), causing list_del corruption (kernel BUG).
> 
> Fix this by:
> 1. Taking a reference on parent in bt_accept_enqueue() and dropping it
>    only when actually unlinked in bt_accept_unlink().
> 2. Checking !list_empty(&bt_sk(sk)->accept_q) inside the accept_q_lock
>    to prevent double unlinking.
> 3. Moving sock_put() outside of the spinlock to avoid sleeping in an
>    atomic context.

These don't look right: eg. sock_put() was not inside spinlock even
before.

> Reported-by: syzbot+534002670dd34a114fdc@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=534002670dd34a114fdc
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> 
> Signed-off-by: Nguyen Ngoc Thang <ngocthang2710.1999@gmail.com>
> ---
>  net/bluetooth/af_bluetooth.c | 23 ++++++++++++++++++-----
>  1 file changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/net/bluetooth/af_bluetooth.c b/net/bluetooth/af_bluetooth.c
> index 411d66f24393..7797b1052808 100644
> --- a/net/bluetooth/af_bluetooth.c
> +++ b/net/bluetooth/af_bluetooth.c
> @@ -224,6 +224,10 @@ void bt_accept_enqueue(struct sock *parent, struct sock *sk, bool bh)
>  	else
>  		lock_sock_nested(sk, SINGLE_DEPTH_NESTING);
>  
> +	/* Hold a reference on parent so it cannot be freed while sk keeps
> +	 * a raw pointer to it via bt_sk(sk)->parent.
> +	 */
> +	sock_hold(parent);
>  	bt_sk(sk)->parent = parent;
>  
>  	spin_lock_bh(&par->accept_q_lock);
> @@ -257,15 +261,24 @@ EXPORT_SYMBOL(bt_accept_enqueue);
>  void bt_accept_unlink(struct sock *sk)
>  {
>  	struct sock *parent = bt_sk(sk)->parent;
> +	bool unlinked = false;
>  
> -	BT_DBG("sk %p state %d", sk, sk->sk_state);
> +	if (!parent)
> +		return;
>  
>  	spin_lock_bh(&bt_sk(parent)->accept_q_lock);
> -	list_del_init(&bt_sk(sk)->accept_q);
> -	sk_acceptq_removed(parent);
> +	if (!list_empty(&bt_sk(sk)->accept_q)) {
> +		list_del_init(&bt_sk(sk)->accept_q);
> +		sk_acceptq_removed(parent);
> +		unlinked = true;
> +	}
>  	spin_unlock_bh(&bt_sk(parent)->accept_q_lock);
> -	bt_sk(sk)->parent = NULL;
> -	sock_put(sk);
> +
> +	if (unlinked) {
> +		bt_sk(sk)->parent = NULL;
> +		sock_put(parent);
> +		sock_put(sk);
> +	}
>  }
>  EXPORT_SYMBOL(bt_accept_unlink);
>  

-- 
Pauli Virtanen