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")
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>

diff --git a/net/can/isotp.c b/net/can/isotp.c
index 9f94ad3..253b244 100644 (file)
--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -1062,27 +1062,31 @@ static int isotp_bind(struct socket *sock, struct sockaddr *uaddr, int len)
        if (len < ISOTP_MIN_NAMELEN)
                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)
@@ -1164,16 +1168,13 @@ static int isotp_getname(struct socket *sock, struct sockaddr *uaddr, int peer)
        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;
 
@@ -1248,6 +1249,22 @@ 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)
 {