mptcp: check the protocol in mptcp_sk() with DEBUG_NET

Fuzzers and static checkers might not detect when mptcp_sk() is used
with a non mptcp_sock structure.

This is similar to the parent commit, where it is easy to use mptcp_sk()
with a TCP sock, e.g. with a subflow sk.

So a new simple check is done when CONFIG_DEBUG_NET is enabled to tell
kernel devs when a non-MPTCP socket is being used as an MPTCP one.
'mptcp_sk()' macro is then defined differently: with an extra WARN to
complain when an unexpected socket is being used.

Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://lore.kernel.org/r/20240223-upstream-net-next-20240223-misc-improvements-v1-4-b6c8a10396bd@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 026ed360bd72d006fca26975f331500ce01b3710..051b100d940312d663d2ed18136b1ddbca06c42e 100644 (file)
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -356,9 +356,15 @@ static inline void msk_owned_by_me(const struct mptcp_sock *msk)
        WARN_ON(_ptr->sk_protocol != IPPROTO_TCP);                              \
        container_of_const(_ptr, struct tcp_sock, inet_conn.icsk_inet.sk);      \
 })
-#endif
+#define mptcp_sk(ptr) ({                                               \
+       typeof(ptr) _ptr = (ptr);                                       \
+       WARN_ON(_ptr->sk_protocol != IPPROTO_MPTCP);                    \
+       container_of_const(_ptr, struct mptcp_sock, sk.icsk_inet.sk);   \
+})
 
+#else /* !CONFIG_DEBUG_NET */
 #define mptcp_sk(ptr) container_of_const(ptr, struct mptcp_sock, sk.icsk_inet.sk)
+#endif
 
 /* the msk socket don't use the backlog, also account for the bulk
  * free memory