[PATCH v5 0/1] Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()

[PATCH v5 0/1] Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()

[Siwei Zhang]

Compared to v2, addresses comments on https://sashiko.dev/#/patchset/20260415204842.2363950-1-oss%40fourdim.xyz .

Compared to v3, rebase against bluetooth-next.

Compared to v4, allocate the channel outside the function and pass it in as an argument to avoid the use-after-free.

Siwei Zhang (1):
  Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()

 include/net/bluetooth/l2cap.h |  8 +++--
 net/bluetooth/6lowpan.c       | 14 ++++-----
 net/bluetooth/l2cap_core.c    | 58 ++++++++++++++++++++++++++++-------
 net/bluetooth/l2cap_sock.c    | 48 +++++++++++++++++------------
 net/bluetooth/smp.c           | 13 +++-----
 5 files changed, 91 insertions(+), 50 deletions(-)

-- 
2.54.0

[PATCH v5 1/1] Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()

[Siwei Zhang]

l2cap_sock_new_connection_cb() accesses l2cap_pi(sk)->chan after
release_sock(parent). Once the parent lock is released, the child
socket sk can be freed by another task.

Allocate the channel outside the func to prevent this.

Fixes: 8ffb929098a5 ("Bluetooth: Remove parent socket usage from l2cap_core.c")
Cc: stable@kernel.org
Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Siwei Zhang <oss@fourdim.xyz>
---
 include/net/bluetooth/l2cap.h |  8 +++--
 net/bluetooth/6lowpan.c       | 14 ++++-----
 net/bluetooth/l2cap_core.c    | 58 ++++++++++++++++++++++++++++-------
 net/bluetooth/l2cap_sock.c    | 48 +++++++++++++++++------------
 net/bluetooth/smp.c           | 13 +++-----
 5 files changed, 91 insertions(+), 50 deletions(-)

diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
index 5172afee5494..f7a11e6431f0 100644
--- a/include/net/bluetooth/l2cap.h
+++ b/include/net/bluetooth/l2cap.h
@@ -619,7 +619,8 @@ struct l2cap_chan {
 struct l2cap_ops {
 	char			*name;
 
-	struct l2cap_chan	*(*new_connection) (struct l2cap_chan *chan);
+	int			(*new_connection)(struct l2cap_chan *chan,
+						  struct l2cap_chan *new_chan);
 	int			(*recv) (struct l2cap_chan * chan,
 					 struct sk_buff *skb);
 	void			(*teardown) (struct l2cap_chan *chan, int err);
@@ -883,9 +884,10 @@ static inline __u16 __next_seq(struct l2cap_chan *chan, __u16 seq)
 	return (seq + 1) % (chan->tx_win_max + 1);
 }
 
-static inline struct l2cap_chan *l2cap_chan_no_new_connection(struct l2cap_chan *chan)
+static inline int l2cap_chan_no_new_connection(struct l2cap_chan *chan,
+					       struct l2cap_chan *new_chan)
 {
-	return NULL;
+	return -EOPNOTSUPP;
 }
 
 static inline int l2cap_chan_no_recv(struct l2cap_chan *chan, struct sk_buff *skb)
diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c
index 23a229ab6a33..286c0b45055b 100644
--- a/net/bluetooth/6lowpan.c
+++ b/net/bluetooth/6lowpan.c
@@ -743,19 +743,19 @@ static inline void chan_ready_cb(struct l2cap_chan *chan)
 	ifup(dev->netdev);
 }
 
-static inline struct l2cap_chan *chan_new_conn_cb(struct l2cap_chan *pchan)
+static inline int chan_new_conn_cb(struct l2cap_chan *pchan,
+				   struct l2cap_chan *chan)
 {
-	struct l2cap_chan *chan;
-
-	chan = chan_create();
-	if (!chan)
-		return NULL;
+	l2cap_chan_set_defaults(chan);
 
+	chan->chan_type = L2CAP_CHAN_CONN_ORIENTED;
+	chan->mode = L2CAP_MODE_LE_FLOWCTL;
+	chan->imtu = 1280;
 	chan->ops = pchan->ops;
 
 	BT_DBG("chan %p pchan %p", chan, pchan);
 
-	return chan;
+	return 0;
 }
 
 static void unregister_dev(struct lowpan_btle_dev *dev)
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index fdccd62ccca8..505f32034971 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4051,10 +4051,16 @@ static void l2cap_connect(struct l2cap_conn *conn, struct l2cap_cmd_hdr *cmd,
 		goto response;
 	}
 
-	chan = pchan->ops->new_connection(pchan);
+	chan = l2cap_chan_create();
 	if (!chan)
 		goto response;
 
+	if (pchan->ops->new_connection(pchan, chan) < 0) {
+		l2cap_chan_put(chan);
+		chan = NULL;
+		goto response;
+	}
+
 	/* For certain devices (ex: HID mouse), support for authentication,
 	 * pairing and bonding is optional. For such devices, inorder to avoid
 	 * the ACL alive for too long after L2CAP disconnection, reset the ACL
@@ -4132,6 +4138,10 @@ static void l2cap_connect(struct l2cap_conn *conn, struct l2cap_cmd_hdr *cmd,
 		chan->num_conf_req++;
 	}
 
+	/* Drop our local ref; __l2cap_chan_add() pinned chan via the conn list. */
+	if (chan)
+		l2cap_chan_put(chan);
+
 	l2cap_chan_unlock(pchan);
 	l2cap_chan_put(pchan);
 }
@@ -4881,6 +4891,7 @@ static int l2cap_le_connect_req(struct l2cap_conn *conn,
 	struct l2cap_le_conn_rsp rsp;
 	struct l2cap_chan *chan, *pchan;
 	u16 dcid, scid, credits, mtu, mps;
+	u16 rsp_mtu, rsp_mps;
 	__le16 psm;
 	u8 result;
 
@@ -4893,6 +4904,8 @@ static int l2cap_le_connect_req(struct l2cap_conn *conn,
 	psm  = req->psm;
 	dcid = 0;
 	credits = 0;
+	rsp_mtu = 0;
+	rsp_mps = 0;
 
 	if (mtu < 23 || mps < 23)
 		return -EPROTO;
@@ -4953,12 +4966,19 @@ static int l2cap_le_connect_req(struct l2cap_conn *conn,
 		goto response_unlock;
 	}
 
-	chan = pchan->ops->new_connection(pchan);
+	chan = l2cap_chan_create();
 	if (!chan) {
 		result = L2CAP_CR_LE_NO_MEM;
 		goto response_unlock;
 	}
 
+	if (pchan->ops->new_connection(pchan, chan) < 0) {
+		l2cap_chan_put(chan);
+		chan = NULL;
+		result = L2CAP_CR_LE_NO_MEM;
+		goto response_unlock;
+	}
+
 	bacpy(&chan->src, &conn->hcon->src);
 	bacpy(&chan->dst, &conn->hcon->dst);
 	chan->src_type = bdaddr_src_type(conn->hcon);
@@ -4974,6 +4994,8 @@ static int l2cap_le_connect_req(struct l2cap_conn *conn,
 
 	dcid = chan->scid;
 	credits = chan->rx_credits;
+	rsp_mtu = chan->imtu;
+	rsp_mps = chan->mps;
 
 	__set_chan_timer(chan, chan->ops->get_sndtimeo(chan));
 
@@ -4993,6 +5015,9 @@ static int l2cap_le_connect_req(struct l2cap_conn *conn,
 		result = L2CAP_CR_LE_SUCCESS;
 	}
 
+	/* Drop our local ref; __l2cap_chan_add() pinned chan via the conn list. */
+	l2cap_chan_put(chan);
+
 response_unlock:
 	l2cap_chan_unlock(pchan);
 	l2cap_chan_put(pchan);
@@ -5001,13 +5026,8 @@ static int l2cap_le_connect_req(struct l2cap_conn *conn,
 		return 0;
 
 response:
-	if (chan) {
-		rsp.mtu = cpu_to_le16(chan->imtu);
-		rsp.mps = cpu_to_le16(chan->mps);
-	} else {
-		rsp.mtu = 0;
-		rsp.mps = 0;
-	}
+	rsp.mtu = cpu_to_le16(rsp_mtu);
+	rsp.mps = cpu_to_le16(rsp_mps);
 
 	rsp.dcid    = cpu_to_le16(dcid);
 	rsp.credits = cpu_to_le16(credits);
@@ -5177,12 +5197,18 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn,
 			continue;
 		}
 
-		chan = pchan->ops->new_connection(pchan);
+		chan = l2cap_chan_create();
 		if (!chan) {
 			result = L2CAP_CR_LE_NO_MEM;
 			continue;
 		}
 
+		if (pchan->ops->new_connection(pchan, chan) < 0) {
+			l2cap_chan_put(chan);
+			result = L2CAP_CR_LE_NO_MEM;
+			continue;
+		}
+
 		bacpy(&chan->src, &conn->hcon->src);
 		bacpy(&chan->dst, &conn->hcon->dst);
 		chan->src_type = bdaddr_src_type(conn->hcon);
@@ -5217,6 +5243,9 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn,
 		} else {
 			l2cap_chan_ready(chan);
 		}
+
+		/* Drop our local ref; __l2cap_chan_add() pinned chan via the conn list. */
+		l2cap_chan_put(chan);
 	}
 
 unlock:
@@ -7399,7 +7428,11 @@ static void l2cap_connect_cfm(struct hci_conn *hcon, u8 status)
 			goto next;
 
 		l2cap_chan_lock(pchan);
-		chan = pchan->ops->new_connection(pchan);
+		chan = l2cap_chan_create();
+		if (chan && pchan->ops->new_connection(pchan, chan) < 0) {
+			l2cap_chan_put(chan);
+			chan = NULL;
+		}
 		if (chan) {
 			bacpy(&chan->src, &hcon->src);
 			bacpy(&chan->dst, &hcon->dst);
@@ -7407,6 +7440,9 @@ static void l2cap_connect_cfm(struct hci_conn *hcon, u8 status)
 			chan->dst_type = dst_type;
 
 			__l2cap_chan_add(conn, chan);
+
+			/* Drop our local ref; __l2cap_chan_add() pinned chan via the conn list. */
+			l2cap_chan_put(chan);
 		}
 
 		l2cap_chan_unlock(pchan);
diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index dede550d6031..598f24c8f704 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -46,7 +46,8 @@ static struct bt_sock_list l2cap_sk_list = {
 static const struct proto_ops l2cap_sock_ops;
 static void l2cap_sock_init(struct sock *sk, struct sock *parent);
 static struct sock *l2cap_sock_alloc(struct net *net, struct socket *sock,
-				     int proto, gfp_t prio, int kern);
+				     int proto, gfp_t prio, int kern,
+				     struct l2cap_chan *chan);
 static void l2cap_sock_cleanup_listen(struct sock *parent);
 
 bool l2cap_is_socket(struct socket *sock)
@@ -1507,12 +1508,13 @@ static void l2cap_sock_cleanup_listen(struct sock *parent)
 	}
 }
 
-static struct l2cap_chan *l2cap_sock_new_connection_cb(struct l2cap_chan *chan)
+static int l2cap_sock_new_connection_cb(struct l2cap_chan *chan,
+					struct l2cap_chan *new_chan)
 {
 	struct sock *sk, *parent = chan->data;
 
 	if (!parent)
-		return NULL;
+		return -EINVAL;
 
 	lock_sock(parent);
 
@@ -1520,15 +1522,15 @@ static struct l2cap_chan *l2cap_sock_new_connection_cb(struct l2cap_chan *chan)
 	if (sk_acceptq_is_full(parent)) {
 		BT_DBG("backlog full %d", parent->sk_ack_backlog);
 		release_sock(parent);
-		return NULL;
+		return -ENOBUFS;
 	}
 
 	sk = l2cap_sock_alloc(sock_net(parent), NULL, BTPROTO_L2CAP,
-			      GFP_ATOMIC, 0);
+			      GFP_ATOMIC, 0, new_chan);
 	if (!sk) {
 		release_sock(parent);
-		return NULL;
-        }
+		return -ENOMEM;
+	}
 
 	bt_sock_reclassify_lock(sk, BTPROTO_L2CAP);
 
@@ -1538,7 +1540,7 @@ static struct l2cap_chan *l2cap_sock_new_connection_cb(struct l2cap_chan *chan)
 
 	release_sock(parent);
 
-	return l2cap_pi(sk)->chan;
+	return 0;
 }
 
 static int l2cap_sock_recv_cb(struct l2cap_chan *chan, struct sk_buff *skb)
@@ -1939,10 +1941,10 @@ static struct proto l2cap_proto = {
 };
 
 static struct sock *l2cap_sock_alloc(struct net *net, struct socket *sock,
-				     int proto, gfp_t prio, int kern)
+				     int proto, gfp_t prio, int kern,
+				     struct l2cap_chan *chan)
 {
 	struct sock *sk;
-	struct l2cap_chan *chan;
 
 	sk = bt_sock_alloc(net, sock, &l2cap_proto, proto, prio, kern);
 	if (!sk)
@@ -1953,14 +1955,11 @@ static struct sock *l2cap_sock_alloc(struct net *net, struct socket *sock,
 
 	INIT_LIST_HEAD(&l2cap_pi(sk)->rx_busy);
 
-	chan = l2cap_chan_create();
-	if (!chan) {
-		sk_free(sk);
-		if (sock)
-			sock->sk = NULL;
-		return NULL;
-	}
-
+	/* The sock owns two refs on chan, matching the puts in
+	 * l2cap_sock_kill() and l2cap_sock_destruct(). The caller keeps
+	 * its own ref independent of these.
+	 */
+	l2cap_chan_hold(chan);
 	l2cap_chan_hold(chan);
 
 	l2cap_pi(sk)->chan = chan;
@@ -1972,6 +1971,7 @@ static int l2cap_sock_create(struct net *net, struct socket *sock, int protocol,
 			     int kern)
 {
 	struct sock *sk;
+	struct l2cap_chan *chan;
 
 	BT_DBG("sock %p", sock);
 
@@ -1986,10 +1986,18 @@ static int l2cap_sock_create(struct net *net, struct socket *sock, int protocol,
 
 	sock->ops = &l2cap_sock_ops;
 
-	sk = l2cap_sock_alloc(net, sock, protocol, GFP_ATOMIC, kern);
-	if (!sk)
+	chan = l2cap_chan_create();
+	if (!chan)
 		return -ENOMEM;
 
+	sk = l2cap_sock_alloc(net, sock, protocol, GFP_ATOMIC, kern, chan);
+	if (!sk) {
+		l2cap_chan_put(chan);
+		return -ENOMEM;
+	}
+	/* Sock has taken its own refs on chan; drop the chan_create() ref. */
+	l2cap_chan_put(chan);
+
 	l2cap_sock_init(sk, NULL);
 	bt_sock_link(&l2cap_sk_list, sk);
 	return 0;
diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index 1739c1989dbd..25cb5dc580bf 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -3204,16 +3204,11 @@ static const struct l2cap_ops smp_chan_ops = {
 	.get_sndtimeo		= l2cap_chan_no_get_sndtimeo,
 };
 
-static inline struct l2cap_chan *smp_new_conn_cb(struct l2cap_chan *pchan)
+static inline int smp_new_conn_cb(struct l2cap_chan *pchan,
+				  struct l2cap_chan *chan)
 {
-	struct l2cap_chan *chan;
-
 	BT_DBG("pchan %p", pchan);
 
-	chan = l2cap_chan_create();
-	if (!chan)
-		return NULL;
-
 	chan->chan_type	= pchan->chan_type;
 	chan->ops	= &smp_chan_ops;
 	chan->scid	= pchan->scid;
@@ -3229,9 +3224,9 @@ static inline struct l2cap_chan *smp_new_conn_cb(struct l2cap_chan *pchan)
 	 */
 	atomic_set(&chan->nesting, L2CAP_NESTING_SMP);
 
-	BT_DBG("created chan %p", chan);
+	BT_DBG("initialised chan %p", chan);
 
-	return chan;
+	return 0;
 }
 
 static const struct l2cap_ops smp_root_chan_ops = {
-- 
2.54.0

RE: Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 1045 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=1098163

---Test result---

Test Summary:
CheckPatch                    PASS      1.67 seconds
GitLint                       PASS      0.34 seconds
SubjectPrefix                 PASS      0.13 seconds
BuildKernel                   PASS      24.93 seconds
CheckAllWarning               PASS      27.79 seconds
CheckSparse                   PASS      26.40 seconds
BuildKernel32                 PASS      24.49 seconds
TestRunnerSetup               PASS      521.38 seconds
TestRunner_l2cap-tester       PASS      376.22 seconds
TestRunner_smp-tester         PASS      17.96 seconds
TestRunner_6lowpan-tester     PASS      50.91 seconds
IncrementalBuild              PASS      24.22 seconds



https://github.com/bluez/bluetooth-next/pull/221

---
Regards,
Linux Bluetooth

[PATCH RESEND v4 1/1] Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()

[Siwei Zhang]

l2cap_sock_new_connection_cb() accesses l2cap_pi(sk)->chan after
release_sock(parent). Once the parent lock is released, the child
socket sk can be freed by another task.

Save the channel pointer into a local variable while the parent lock
is still held to prevent this.

Fixes: 8ffb929098a5 ("Bluetooth: Remove parent socket usage from l2cap_core.c")
Cc: stable@kernel.org
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Siwei Zhang <oss@fourdim.xyz>
---
 net/bluetooth/6lowpan.c    |  5 +++++
 net/bluetooth/l2cap_core.c | 12 ++++++++++++
 net/bluetooth/l2cap_sock.c | 13 ++++++++++++-
 net/bluetooth/smp.c        |  5 +++++
 4 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c
index 23a229ab6a33..71c1c04b61e5 100644
--- a/net/bluetooth/6lowpan.c
+++ b/net/bluetooth/6lowpan.c
@@ -755,6 +755,11 @@ static inline struct l2cap_chan *chan_new_conn_cb(struct l2cap_chan *pchan)
 
 	BT_DBG("chan %p pchan %p", chan, pchan);
 
+	/* Match the put that the caller of ops->new_connection() performs
+	 * once it is done with the returned channel pointer.
+	 */
+	l2cap_chan_hold(chan);
+
 	return chan;
 }
 
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 7701528f1167..0f6c3c651207 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4071,6 +4071,9 @@ static void l2cap_connect(struct l2cap_conn *conn, struct l2cap_cmd_hdr *cmd,
 
 	__l2cap_chan_add(conn, chan);
 
+	/* Drop the ops->new_connection() ref; conn list now pins chan. */
+	l2cap_chan_put(chan);
+
 	dcid = chan->scid;
 
 	__set_chan_timer(chan, chan->ops->get_sndtimeo(chan));
@@ -4970,6 +4973,9 @@ static int l2cap_le_connect_req(struct l2cap_conn *conn,
 
 	__l2cap_chan_add(conn, chan);
 
+	/* Drop the ops->new_connection() ref; conn list now pins chan. */
+	l2cap_chan_put(chan);
+
 	l2cap_le_flowctl_init(chan, __le16_to_cpu(req->credits));
 
 	dcid = chan->scid;
@@ -5194,6 +5200,9 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn,
 
 		__l2cap_chan_add(conn, chan);
 
+		/* Drop the ops->new_connection() ref; conn list now pins chan. */
+		l2cap_chan_put(chan);
+
 		l2cap_ecred_init(chan, __le16_to_cpu(req->credits));
 
 		/* Init response */
@@ -7407,6 +7416,9 @@ static void l2cap_connect_cfm(struct hci_conn *hcon, u8 status)
 			chan->dst_type = dst_type;
 
 			__l2cap_chan_add(conn, chan);
+
+			/* Drop the ops->new_connection() ref; conn list now pins chan. */
+			l2cap_chan_put(chan);
 		}
 
 		l2cap_chan_unlock(pchan);
diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index cf590a67d364..295c79cf5cf3 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1497,6 +1497,7 @@ static void l2cap_sock_cleanup_listen(struct sock *parent)
 static struct l2cap_chan *l2cap_sock_new_connection_cb(struct l2cap_chan *chan)
 {
 	struct sock *sk, *parent = chan->data;
+	struct l2cap_chan *child_chan;
 
 	if (!parent)
 		return NULL;
@@ -1523,9 +1524,19 @@ static struct l2cap_chan *l2cap_sock_new_connection_cb(struct l2cap_chan *chan)
 
 	bt_accept_enqueue(parent, sk, false);
 
+	child_chan = l2cap_pi(sk)->chan;
+
+	/* Pin the channel for the caller. Once release_sock(parent) returns,
+	 * userspace can accept(2) and immediately close(2) the child socket,
+	 * which would drop the socket's references on the channel and free
+	 * it before the caller (e.g. l2cap_connect_req()) is done using the
+	 * returned pointer. The matching put is the caller's responsibility.
+	 */
+	l2cap_chan_hold(child_chan);
+
 	release_sock(parent);
 
-	return l2cap_pi(sk)->chan;
+	return child_chan;
 }
 
 static int l2cap_sock_recv_cb(struct l2cap_chan *chan, struct sk_buff *skb)
diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index 1739c1989dbd..9796c3030434 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -3231,6 +3231,11 @@ static inline struct l2cap_chan *smp_new_conn_cb(struct l2cap_chan *pchan)
 
 	BT_DBG("created chan %p", chan);
 
+	/* Match the put that the caller of ops->new_connection() performs
+	 * once it is done with the returned channel pointer.
+	 */
+	l2cap_chan_hold(chan);
+
 	return chan;
 }
 
-- 
2.54.0

RE: Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 1708 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=1092984

---Test result---

Test Summary:
CheckPatch                    PASS      1.40 seconds
GitLint                       FAIL      0.34 seconds
SubjectPrefix                 PASS      0.13 seconds
BuildKernel                   PASS      26.78 seconds
CheckAllWarning               PASS      27.90 seconds
CheckSparse                   PASS      26.85 seconds
BuildKernel32                 PASS      24.71 seconds
TestRunnerSetup               PASS      524.97 seconds
TestRunner_l2cap-tester       PASS      376.41 seconds
TestRunner_smp-tester         PASS      18.41 seconds
TestRunner_6lowpan-tester     PASS      51.29 seconds
IncrementalBuild              PASS      23.95 seconds

Details
##############################
Test: GitLint - FAIL
Desc: Run gitlint
Output:
[RESEND,v4,1/1] Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()

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1: T1 Title exceeds max length (86>80): "[RESEND,v4,1/1] Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()"


https://github.com/bluez/bluetooth-next/pull/172

---
Regards,
Linux Bluetooth

[PATCH 1/1] Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()

[Siwei Zhang]

l2cap_sock_new_connection_cb() accesses l2cap_pi(sk)->chan after
release_sock(parent). Once the parent lock is released, the child
socket sk can be freed by another task.

Save the channel pointer into a local variable while the parent lock
is still held to prevent this.

Fixes: 8ffb929098a5 ("Bluetooth: Remove parent socket usage from l2cap_core.c")
Cc: stable@kernel.org
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Siwei Zhang <oss@fourdim.xyz>
---
 net/bluetooth/6lowpan.c    |  5 +++++
 net/bluetooth/l2cap_core.c | 12 ++++++++++++
 net/bluetooth/l2cap_sock.c | 13 ++++++++++++-
 net/bluetooth/smp.c        |  5 +++++
 4 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c
index 23a229ab6a33..71c1c04b61e5 100644
--- a/net/bluetooth/6lowpan.c
+++ b/net/bluetooth/6lowpan.c
@@ -755,6 +755,11 @@ static inline struct l2cap_chan *chan_new_conn_cb(struct l2cap_chan *pchan)
 
 	BT_DBG("chan %p pchan %p", chan, pchan);
 
+	/* Match the put that the caller of ops->new_connection() performs
+	 * once it is done with the returned channel pointer.
+	 */
+	l2cap_chan_hold(chan);
+
 	return chan;
 }
 
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 7701528f1167..0f6c3c651207 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4071,6 +4071,9 @@ static void l2cap_connect(struct l2cap_conn *conn, struct l2cap_cmd_hdr *cmd,
 
 	__l2cap_chan_add(conn, chan);
 
+	/* Drop the ops->new_connection() ref; conn list now pins chan. */
+	l2cap_chan_put(chan);
+
 	dcid = chan->scid;
 
 	__set_chan_timer(chan, chan->ops->get_sndtimeo(chan));
@@ -4970,6 +4973,9 @@ static int l2cap_le_connect_req(struct l2cap_conn *conn,
 
 	__l2cap_chan_add(conn, chan);
 
+	/* Drop the ops->new_connection() ref; conn list now pins chan. */
+	l2cap_chan_put(chan);
+
 	l2cap_le_flowctl_init(chan, __le16_to_cpu(req->credits));
 
 	dcid = chan->scid;
@@ -5194,6 +5200,9 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn,
 
 		__l2cap_chan_add(conn, chan);
 
+		/* Drop the ops->new_connection() ref; conn list now pins chan. */
+		l2cap_chan_put(chan);
+
 		l2cap_ecred_init(chan, __le16_to_cpu(req->credits));
 
 		/* Init response */
@@ -7407,6 +7416,9 @@ static void l2cap_connect_cfm(struct hci_conn *hcon, u8 status)
 			chan->dst_type = dst_type;
 
 			__l2cap_chan_add(conn, chan);
+
+			/* Drop the ops->new_connection() ref; conn list now pins chan. */
+			l2cap_chan_put(chan);
 		}
 
 		l2cap_chan_unlock(pchan);
diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index cf590a67d364..295c79cf5cf3 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1497,6 +1497,7 @@ static void l2cap_sock_cleanup_listen(struct sock *parent)
 static struct l2cap_chan *l2cap_sock_new_connection_cb(struct l2cap_chan *chan)
 {
 	struct sock *sk, *parent = chan->data;
+	struct l2cap_chan *child_chan;
 
 	if (!parent)
 		return NULL;
@@ -1523,9 +1524,19 @@ static struct l2cap_chan *l2cap_sock_new_connection_cb(struct l2cap_chan *chan)
 
 	bt_accept_enqueue(parent, sk, false);
 
+	child_chan = l2cap_pi(sk)->chan;
+
+	/* Pin the channel for the caller. Once release_sock(parent) returns,
+	 * userspace can accept(2) and immediately close(2) the child socket,
+	 * which would drop the socket's references on the channel and free
+	 * it before the caller (e.g. l2cap_connect_req()) is done using the
+	 * returned pointer. The matching put is the caller's responsibility.
+	 */
+	l2cap_chan_hold(child_chan);
+
 	release_sock(parent);
 
-	return l2cap_pi(sk)->chan;
+	return child_chan;
 }
 
 static int l2cap_sock_recv_cb(struct l2cap_chan *chan, struct sk_buff *skb)
diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index 1739c1989dbd..9796c3030434 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -3231,6 +3231,11 @@ static inline struct l2cap_chan *smp_new_conn_cb(struct l2cap_chan *pchan)
 
 	BT_DBG("created chan %p", chan);
 
+	/* Match the put that the caller of ops->new_connection() performs
+	 * once it is done with the returned channel pointer.
+	 */
+	l2cap_chan_hold(chan);
+
 	return chan;
 }
 
-- 
2.54.0

RE: Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 1045 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=1092493

---Test result---

Test Summary:
CheckPatch                    PASS      2.09 seconds
GitLint                       PASS      0.32 seconds
SubjectPrefix                 PASS      0.12 seconds
BuildKernel                   PASS      25.70 seconds
CheckAllWarning               PASS      28.70 seconds
CheckSparse                   PASS      27.32 seconds
BuildKernel32                 PASS      25.31 seconds
TestRunnerSetup               PASS      561.40 seconds
TestRunner_l2cap-tester       PASS      378.21 seconds
TestRunner_smp-tester         PASS      18.06 seconds
TestRunner_6lowpan-tester     PASS      51.06 seconds
IncrementalBuild              PASS      24.97 seconds



https://github.com/bluez/bluetooth-next/pull/163

---
Regards,
Linux Bluetooth

[PATCH 1/1] Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()

[Siwei Zhang]

l2cap_sock_new_connection_cb() accesses l2cap_pi(sk)->chan after
release_sock(parent). Once the parent lock is released, the child
socket sk can be freed by another task.

Save the channel pointer into a local variable while the parent lock
is still held to prevent this.

Fixes: 8ffb929098a5 ("Bluetooth: Remove parent socket usage from l2cap_core.c")
Cc: stable@kernel.org
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Siwei Zhang <oss@fourdim.xyz>
---
 net/bluetooth/6lowpan.c    |  5 +++++
 net/bluetooth/l2cap_core.c | 12 ++++++++++++
 net/bluetooth/l2cap_sock.c | 13 ++++++++++++-
 net/bluetooth/smp.c        |  5 +++++
 4 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c
index 2f03b780b40d..bbe67bd73f9c 100644
--- a/net/bluetooth/6lowpan.c
+++ b/net/bluetooth/6lowpan.c
@@ -755,6 +755,11 @@ static inline struct l2cap_chan *chan_new_conn_cb(struct l2cap_chan *pchan)
 
 	BT_DBG("chan %p pchan %p", chan, pchan);
 
+	/* Match the put that the caller of ops->new_connection() performs
+	 * once it is done with the returned channel pointer.
+	 */
+	l2cap_chan_hold(chan);
+
 	return chan;
 }
 
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 95c65fece39b..fc663386872c 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4071,6 +4071,9 @@ static void l2cap_connect(struct l2cap_conn *conn, struct l2cap_cmd_hdr *cmd,
 
 	__l2cap_chan_add(conn, chan);
 
+	/* Drop the ops->new_connection() ref; conn list now pins chan. */
+	l2cap_chan_put(chan);
+
 	dcid = chan->scid;
 
 	__set_chan_timer(chan, chan->ops->get_sndtimeo(chan));
@@ -4978,6 +4981,9 @@ static int l2cap_le_connect_req(struct l2cap_conn *conn,
 
 	__l2cap_chan_add(conn, chan);
 
+	/* Drop the ops->new_connection() ref; conn list now pins chan. */
+	l2cap_chan_put(chan);
+
 	l2cap_le_flowctl_init(chan, __le16_to_cpu(req->credits));
 
 	dcid = chan->scid;
@@ -5202,6 +5208,9 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn,
 
 		__l2cap_chan_add(conn, chan);
 
+		/* Drop the ops->new_connection() ref; conn list now pins chan. */
+		l2cap_chan_put(chan);
+
 		l2cap_ecred_init(chan, __le16_to_cpu(req->credits));
 
 		/* Init response */
@@ -7402,6 +7411,9 @@ static void l2cap_connect_cfm(struct hci_conn *hcon, u8 status)
 			chan->dst_type = dst_type;
 
 			__l2cap_chan_add(conn, chan);
+
+			/* Drop the ops->new_connection() ref; conn list now pins chan. */
+			l2cap_chan_put(chan);
 		}
 
 		l2cap_chan_unlock(pchan);
diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index 71e8c1b45bce..355fad9e2955 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1497,6 +1497,7 @@ static void l2cap_sock_cleanup_listen(struct sock *parent)
 static struct l2cap_chan *l2cap_sock_new_connection_cb(struct l2cap_chan *chan)
 {
 	struct sock *sk, *parent = chan->data;
+	struct l2cap_chan *child_chan;
 
 	lock_sock(parent);
 
@@ -1520,9 +1521,19 @@ static struct l2cap_chan *l2cap_sock_new_connection_cb(struct l2cap_chan *chan)
 
 	bt_accept_enqueue(parent, sk, false);
 
+	child_chan = l2cap_pi(sk)->chan;
+
+	/* Pin the channel for the caller. Once release_sock(parent) returns,
+	 * userspace can accept(2) and immediately close(2) the child socket,
+	 * which would drop the socket's references on the channel and free
+	 * it before the caller (e.g. l2cap_connect_req()) is done using the
+	 * returned pointer. The matching put is the caller's responsibility.
+	 */
+	l2cap_chan_hold(child_chan);
+
 	release_sock(parent);
 
-	return l2cap_pi(sk)->chan;
+	return child_chan;
 }
 
 static int l2cap_sock_recv_cb(struct l2cap_chan *chan, struct sk_buff *skb)
diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index 98f1da4f5f55..32761d3d252e 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -3261,6 +3261,11 @@ static inline struct l2cap_chan *smp_new_conn_cb(struct l2cap_chan *pchan)
 
 	BT_DBG("created chan %p", chan);
 
+	/* Match the put that the caller of ops->new_connection() performs
+	 * once it is done with the returned channel pointer.
+	 */
+	l2cap_chan_hold(chan);
+
 	return chan;
 }
 
-- 
2.54.0

RE: Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 555 bytes --]

This is an automated email and please do not reply to this email.

Dear Submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
While preparing the CI tests, the patches you submitted couldn't be applied to the current HEAD of the repository.

----- Output -----

error: patch failed: net/bluetooth/l2cap_sock.c:1497
error: net/bluetooth/l2cap_sock.c: patch does not apply
hint: Use 'git am --show-current-patch' to see the failed patch

Please resolve the issue and submit the patches again.


---
Regards,
Linux Bluetooth