[PATCH] Bluetooth: L2CAP: access chan->conn safely in get/setsockopt

Since commit b66774b48dd9 ("Bluetooth: L2CAP: Fix UAF in channel timeout by holding conn ref")
l2cap_chan::conn has held reference and remains non-NULL also after the
corresponding hci_conn is deleted.  In this state accessing various
fields eg. hci_conn::hdev is invalid, which leads to KASAN crash in
l2cap_sock_setsockopt() access of conn->hcon->hdev.

Check l2cap_chan::conn.hcon corresponds to an alive hci_conn before
trying to use it in l2cap_sock.c.  Hold l2cap_chan_lock() in
getsockopt/setsockopt to ensure it stays alive, and to avoid data races
in l2cap_chan fields.

Fixes: b66774b48dd9 ("Bluetooth: L2CAP: Fix UAF in channel timeout by holding conn ref")
Reported-by: [email protected]
Link: https://syzkaller.appspot.com/bug?extid=b106284c2a0b7bc80cf9
Signed-off-by: Pauli Virtanen <[email protected]>
---
 net/bluetooth/l2cap_sock.c | 64 ++++++++++++++++++++++++++++----------
 1 file changed, 48 insertions(+), 16 deletions(-)

diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index 735167f73f31..cca6201f9cdb 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -436,11 +436,26 @@ static int l2cap_get_mode(struct l2cap_chan *chan)
 	return -EINVAL;
 }
 
+static struct l2cap_conn *l2cap_chan_conn(struct l2cap_chan *chan)
+{
+	lockdep_assert_held(&chan->lock);
+
+	/* l2cap_conn_del() sets FLAG_DEL while holding chan->lock before
+	 * conn->hcon is deleted. If not set and conn is non-NULL, conn->hcon
+	 * remains alive during this chan->lock critical section.
+	 */
+	if (test_bit(FLAG_DEL, &chan->flags))
+		return NULL;
+
+	return chan->conn;
+}
+
 static int l2cap_sock_getsockopt_old(struct socket *sock, int optname,
 				     sockopt_t *sopt)
 {
 	struct sock *sk = sock->sk;
 	struct l2cap_chan *chan = l2cap_pi(sk)->chan;
+	struct l2cap_conn *conn;
 	struct l2cap_options opts;
 	struct l2cap_conninfo cinfo;
 	int err = 0;
@@ -451,6 +466,7 @@ static int l2cap_sock_getsockopt_old(struct socket *sock, int optname,
 
 	len = sopt->optlen;
 
+	l2cap_chan_lock(chan);
 	lock_sock(sk);
 
 	switch (optname) {
@@ -537,9 +553,15 @@ static int l2cap_sock_getsockopt_old(struct socket *sock, int optname,
 			break;
 		}
 
+		conn = l2cap_chan_conn(chan);
+		if (!conn) {
+			err = -ENOTCONN;
+			break;
+		}
+
 		memset(&cinfo, 0, sizeof(cinfo));
-		cinfo.hci_handle = chan->conn->hcon->handle;
-		memcpy(cinfo.dev_class, chan->conn->hcon->dev_class, 3);
+		cinfo.hci_handle = conn->hcon->handle;
+		memcpy(cinfo.dev_class, conn->hcon->dev_class, 3);
 
 		len = min(len, sizeof(cinfo));
 		if (copy_to_iter(&cinfo, len, &sopt->iter_out) != len)
@@ -553,6 +575,8 @@ static int l2cap_sock_getsockopt_old(struct socket *sock, int optname,
 	}
 
 	release_sock(sk);
+	l2cap_chan_unlock(chan);
+
 	return err;
 }
 
@@ -561,6 +585,7 @@ static int l2cap_sock_getsockopt(struct socket *sock, int level, int optname,
 {
 	struct sock *sk = sock->sk;
 	struct l2cap_chan *chan = l2cap_pi(sk)->chan;
+	struct l2cap_conn *conn;
 	struct bt_security sec;
 	struct bt_power pwr;
 	int len, mode, err = 0;
@@ -578,6 +603,7 @@ static int l2cap_sock_getsockopt(struct socket *sock, int level, int optname,
 
 	len = sopt->optlen;
 
+	l2cap_chan_lock(chan);
 	lock_sock(sk);
 
 	switch (optname) {
@@ -589,12 +615,14 @@ static int l2cap_sock_getsockopt(struct socket *sock, int level, int optname,
 			break;
 		}
 
+		conn = l2cap_chan_conn(chan);
+
 		memset(&sec, 0, sizeof(sec));
-		if (chan->conn) {
-			sec.level = chan->conn->hcon->sec_level;
+		if (conn) {
+			sec.level = conn->hcon->sec_level;
 
 			if (sk->sk_state == BT_CONNECTED)
-				sec.key_size = chan->conn->hcon->enc_key_size;
+				sec.key_size = conn->hcon->enc_key_size;
 		} else {
 			sec.level = chan->sec_level;
 		}
@@ -678,12 +706,14 @@ static int l2cap_sock_getsockopt(struct socket *sock, int level, int optname,
 		break;
 
 	case BT_PHY:
-		if (sk->sk_state != BT_CONNECTED) {
+		conn = l2cap_chan_conn(chan);
+
+		if (sk->sk_state != BT_CONNECTED || !conn) {
 			err = -ENOTCONN;
 			break;
 		}
 
-		opt = hci_conn_get_phy(chan->conn->hcon);
+		opt = hci_conn_get_phy(conn->hcon);
 
 		if (copy_to_iter(&opt, sizeof(opt), &sopt->iter_out) !=
 		    sizeof(opt))
@@ -719,6 +749,7 @@ static int l2cap_sock_getsockopt(struct socket *sock, int level, int optname,
 	}
 
 	release_sock(sk);
+	l2cap_chan_unlock(chan);
 	return err;
 }
 
@@ -749,6 +780,7 @@ static int l2cap_sock_setsockopt_old(struct socket *sock, int optname,
 
 	BT_DBG("sk %p", sk);
 
+	l2cap_chan_lock(chan);
 	lock_sock(sk);
 
 	switch (optname) {
@@ -850,6 +882,7 @@ static int l2cap_sock_setsockopt_old(struct socket *sock, int optname,
 	}
 
 	release_sock(sk);
+	l2cap_chan_unlock(chan);
 	return err;
 }
 
@@ -913,6 +946,7 @@ static int l2cap_sock_setsockopt(struct socket *sock, int level, int optname,
 	if (level != SOL_BLUETOOTH)
 		return -ENOPROTOOPT;
 
+	l2cap_chan_lock(chan);
 	lock_sock(sk);
 
 	switch (optname) {
@@ -938,11 +972,10 @@ static int l2cap_sock_setsockopt(struct socket *sock, int level, int optname,
 
 		chan->sec_level = sec.level;
 
-		if (!chan->conn)
+		conn = l2cap_chan_conn(chan);
+		if (!conn)
 			break;
 
-		conn = chan->conn;
-
 		/* change security for LE channels */
 		if (chan->scid == L2CAP_CID_ATT) {
 			if (smp_conn_security(conn->hcon, sec.level)) {
@@ -997,7 +1030,8 @@ static int l2cap_sock_setsockopt(struct socket *sock, int level, int optname,
 		}
 
 		if (opt == BT_FLUSHABLE_OFF) {
-			conn = chan->conn;
+			conn = l2cap_chan_conn(chan);
+
 			/* proceed further only when we have l2cap_conn and
 			   No Flush support in the LM */
 			if (!conn || !lmp_no_flush_capable(conn->hcon->hdev)) {
@@ -1083,7 +1117,8 @@ static int l2cap_sock_setsockopt(struct socket *sock, int level, int optname,
 		break;
 
 	case BT_PHY:
-		if (sk->sk_state != BT_CONNECTED) {
+		conn = l2cap_chan_conn(chan);
+		if (sk->sk_state != BT_CONNECTED || !conn) {
 			err = -ENOTCONN;
 			break;
 		}
@@ -1093,10 +1128,6 @@ static int l2cap_sock_setsockopt(struct socket *sock, int level, int optname,
 		if (err)
 			break;
 
-		if (!chan->conn)
-			break;
-
-		conn = chan->conn;
 		err = hci_conn_set_phy(conn->hcon, phys);
 		break;
 
@@ -1139,6 +1170,7 @@ static int l2cap_sock_setsockopt(struct socket *sock, int level, int optname,
 	}
 
 	release_sock(sk);
+	l2cap_chan_unlock(chan);
 	return err;
 }
 
-- 
2.55.0