[BACKPORT stable Linux-5.10.y 1/2] can: isotp: prevent race between isotp_bind() and isotp_setsockopt()

[Oliver Hartkopp <socketcan@hartkopp.net>]

Upstream commit 2b17c400aeb44daf041627722581ade527bb3c1d

The fixes tag of the uptream patch points to commit 921ca574cd38 ("can:
isotp: add SF_BROADCAST support for functional addressing") which showed
up in Linux 5.11 but the described issue already existed in Linux 5.10.

Norbert Slusarek writes:

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: e057dd3fc20f ("can: add ISO 15765-2:2016 transport protocol")
Link: https://lore.kernel.org/r/trinity-e6ae9efa-9afb-4326-84c0-f3609b9b8168-1620773528307@3c-app-gmx-bs06
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>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 net/can/isotp.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/net/can/isotp.c b/net/can/isotp.c
index 37db4d232313..3f11d2b314b6 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -1191,20 +1191,17 @@ static int isotp_getname(struct socket *sock, struct sockaddr *uaddr, int peer)
 	addr->can_addr.tp.tx_id = so->txid;
 
 	return ISOTP_MIN_NAMELEN;
 }
 
-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;
 
 	switch (optname) {
 	case CAN_ISOTP_OPTS:
@@ -1275,10 +1272,26 @@ 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)
 {
 	struct sock *sk = sock->sk;
 	struct isotp_sock *so = isotp_sk(sk);
-- 
2.30.2