net: tcp_probe: kprobes: adapt jtcp_rcv_established signature

This patches fixes a rather unproblematic function signature mismatch
as the const specifier was missing for the th variable; and next to
that it adds a build-time assertion so that future function signature
mismatches for kprobes will not end badly, similarly as commit 22222997
("net: sctp: add build check for sctp_sf_eat_sack_6_2/jsctp_sf_eat_sack")
did it for SCTP.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 1 deletions

diff --git a/net/ipv4/tcp_probe.c b/net/ipv4/tcp_probe.c
index fae788b5b03e..a2392f48ba35 100644
--- a/net/ipv4/tcp_probe.c
+++ b/net/ipv4/tcp_probe.c
@@ -92,7 +92,7 @@ static inline int tcp_probe_avail(void)
  * Note: arguments must match tcp_rcv_established()!
  */
 static int jtcp_rcv_established(struct sock *sk, struct sk_buff *skb,
-                               struct tcphdr *th, unsigned int len)
+                                const struct tcphdr *th, unsigned int len)
 {
         const struct tcp_sock *tp = tcp_sk(sk);
         const struct inet_sock *inet = inet_sk(sk);
@@ -225,6 +225,13 @@ static __init int tcpprobe_init(void)
 {
         int ret = -ENOMEM;
 
+        /* Warning: if the function signature of tcp_rcv_established,
+         * has been changed, you also have to change the signature of
+         * jtcp_rcv_established, otherwise you end up right here!
+         */
+        BUILD_BUG_ON(__same_type(tcp_rcv_established,
+                                 jtcp_rcv_established) == 0);
+
         init_waitqueue_head(&tcp_probe.wait);
         spin_lock_init(&tcp_probe.lock);