can: isotp: restore accidentally removed MSG_PEEK feature

JIRA: https://issues.redhat.com/browse/RHEL-80832

commit e382fea
Author: Oliver Hartkopp <[email protected]>
Date:   Mon Mar 28 13:36:11 2022 +0200

    can: isotp: restore accidentally removed MSG_PEEK feature

    In commit 42bf50a ("can: isotp: support MSG_TRUNC flag when
    reading from socket") a new check for recvmsg flags has been
    introduced that only checked for the flags that are handled in
    isotp_recvmsg() itself.

    This accidentally removed the MSG_PEEK feature flag which is processed
    later in the call chain in __skb_try_recv_from_queue().

    Add MSG_PEEK to the set of valid flags to restore the feature.

    Fixes: 42bf50a ("can: isotp: support MSG_TRUNC flag when reading from socket")
    Link: linux-can/can-utils#347 (comment)
    Link: https://lore.kernel.org/all/[email protected]
    Reported-by: Derek Will <[email protected]>
    Suggested-by: Derek Will <[email protected]>
    Tested-by: Derek Will <[email protected]>
    Signed-off-by: Oliver Hartkopp <[email protected]>
    Signed-off-by: Marc Kleine-Budde <[email protected]>

Signed-off-by: Radu Rendec <[email protected]>

Author: rrendec

net/can/isotp.c

@@ -1107,7 +1107,7 @@ static int isotp_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
 	struct isotp_sock *so = isotp_sk(sk);
 	int ret = 0;
 
-	if (flags & ~(MSG_DONTWAIT | MSG_TRUNC))
+	if (flags & ~(MSG_DONTWAIT | MSG_TRUNC | MSG_PEEK))
 		return -EINVAL;
 
 	if (!so->bound)