[PATCH] can: isotp: prevent race between isotp_bind and isotp_setsockopt

[Norbert Slusarek <nslusarek@gmx.net>]

From: Norbert Slusarek <nslusarek@gmx.net>
Date: Wed, 12 May 2021 00:43:54 +0200
Subject: [PATCH] can: isotp: prevent race between isotp_bind and isotp_setsockopt

A race condition was found in isotp_setsockopt() which allows to
change socket options after the socket was bound.
For the specific case of SF_BROADCAST support, this might lead to possible
use-after-free because can_rx_unregister() is not called.

Checking for the flag under the socket lock in isotp_bind()
and taking the lock in isotp_setsockopt() fixes the issue.

Fixes: 921ca574cd38 ("can: isotp: add SF_BROADCAST support for functional addressing")
Reported-by: Norbert Slusarek <nslusarek@gmx.net>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Norbert Slusarek <nslusarek@gmx.net>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 net/can/isotp.c | 49 +++++++++++++++++++++++++++++++++----------------
 1 file changed, 33 insertions(+), 16 deletions(-)

diff --git a/net/can/isotp.c b/net/can/isotp.c
index 15ea1234d457..6cc05940d0b7 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -1059,27 +1059,31 @@ static int isotp_bind(struct socket *sock, struct sockaddr *uaddr, int len)
 	if (len < CAN_REQUIRED_SIZE(struct sockaddr_can, can_addr.tp))
 		return -EINVAL;

+	if (addr->can_addr.tp.tx_id & (CAN_ERR_FLAG | CAN_RTR_FLAG))
+		return -EADDRNOTAVAIL;
+
+	if (!addr->can_ifindex)
+		return -ENODEV;
+
+	lock_sock(sk);
+
 	/* do not register frame reception for functional addressing */
 	if (so->opt.flags & CAN_ISOTP_SF_BROADCAST)
 		do_rx_reg = 0;

 	/* do not validate rx address for functional addressing */
 	if (do_rx_reg) {
-		if (addr->can_addr.tp.rx_id == addr->can_addr.tp.tx_id)
-			return -EADDRNOTAVAIL;
+		if (addr->can_addr.tp.rx_id == addr->can_addr.tp.tx_id) {
+			err = -EADDRNOTAVAIL;
+			goto out;
+		}

-		if (addr->can_addr.tp.rx_id & (CAN_ERR_FLAG | CAN_RTR_FLAG))
-			return -EADDRNOTAVAIL;
+		if (addr->can_addr.tp.rx_id & (CAN_ERR_FLAG | CAN_RTR_FLAG)) {
+			err = -EADDRNOTAVAIL;
+			goto out;
+		}
 	}

-	if (addr->can_addr.tp.tx_id & (CAN_ERR_FLAG | CAN_RTR_FLAG))
-		return -EADDRNOTAVAIL;
-
-	if (!addr->can_ifindex)
-		return -ENODEV;
-
-	lock_sock(sk);
-
 	if (so->bound && addr->can_ifindex == so->ifindex &&
 	    addr->can_addr.tp.rx_id == so->rxid &&
 	    addr->can_addr.tp.tx_id == so->txid)
@@ -1161,16 +1165,13 @@ static int isotp_getname(struct socket *sock, struct sockaddr *uaddr, int peer)
 	return sizeof(*addr);
 }

-static int isotp_setsockopt(struct socket *sock, int level, int optname,
+static int isotp_setsockopt_locked(struct socket *sock, int level, int optname,
 			    sockptr_t optval, unsigned int optlen)
 {
 	struct sock *sk = sock->sk;
 	struct isotp_sock *so = isotp_sk(sk);
 	int ret = 0;

-	if (level != SOL_CAN_ISOTP)
-		return -EINVAL;
-
 	if (so->bound)
 		return -EISCONN;

@@ -1245,6 +1246,22 @@ static int isotp_setsockopt(struct socket *sock, int level, int optname,
 	return ret;
 }

+static int isotp_setsockopt(struct socket *sock, int level, int optname,
+			    sockptr_t optval, unsigned int optlen)
+
+{
+	struct sock *sk = sock->sk;
+	int ret;
+
+	if (level != SOL_CAN_ISOTP)
+		return -EINVAL;
+
+	lock_sock(sk);
+	ret = isotp_setsockopt_locked(sock, level, optname, optval, optlen);
+	release_sock(sk);
+	return ret;
+}
+
 static int isotp_getsockopt(struct socket *sock, int level, int optname,
 			    char __user *optval, int __user *optlen)
 {
--
2.27.0