[PATCH v2] Bluetooth: af_bluetooth: Fix double list_del and UAF in accept_q

[PATCH v2] 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>
---
v2:
 - Add !list_empty() check inside accept_q_lock to prevent double list_del.
 - Move sock_put() outside of the spinlock to avoid sleeping in atomic context (suggested by Paavo Helde).

 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: [v2] Bluetooth: af_bluetooth: Fix double list_del and UAF in accept_q

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 2525 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/1168407/

---Test result---

Test Summary:
CheckPatch                    PASS      0.46 seconds
VerifyFixes                   PASS      0.06 seconds
VerifySignedoff               PASS      0.06 seconds
GitLint                       FAIL      0.18 seconds
SubjectPrefix                 PASS      0.05 seconds
BuildKernel                   PASS      21.71 seconds
CheckAllWarning               PASS      25.22 seconds
CheckSparse                   PASS      28.62 seconds
BuildKernel32                 PASS      27.86 seconds
CheckKernelLLVM               PASS      25.40 seconds
TestRunnerSetup               PASS      571.80 seconds
TestRunner_l2cap-tester       PASS      17.28 seconds
TestRunner_iso-tester         PASS      25.42 seconds
TestRunner_bnep-tester        PASS      2.77 seconds
TestRunner_mgmt-tester        FAIL      56.51 seconds
TestRunner_rfcomm-tester      PASS      4.01 seconds
TestRunner_sco-tester         PASS      7.07 seconds
TestRunner_ioctl-tester       PASS      4.15 seconds
TestRunner_mesh-tester        FAIL      7.63 seconds
TestRunner_smp-tester         PASS      3.93 seconds
TestRunner_userchan-tester    PASS      2.83 seconds
TestRunner_6lowpan-tester     PASS      3.94 seconds
IncrementalBuild              PASS      21.75 seconds

Details
##############################
Test: GitLint - FAIL
Desc: Run gitlint
Output:
[v2] Bluetooth: af_bluetooth: Fix double list_del and UAF in accept_q

28: B1 Line exceeds max length (106>80): " - Move sock_put() outside of the spinlock to avoid sleeping in atomic context (suggested by Paavo Helde)."
##############################
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       0.015 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    2.525 seconds
Mesh - Send cancel - 2                               Timed out    2.000 seconds


https://github.com/bluez/bluetooth-next/pull/787

---
Regards,
Linux Bluetooth