From: Alexander Bluhm <alexander.bluhm@gmx.net>
Subject: Re: const sockaddr in tcp syn cache
To: tech@openbsd.org
Date: Fri, 19 Jan 2024 15:01:12 +0100

On Fri, Jan 19, 2024 at 02:47:53PM +0100, Alexander Bluhm wrote:
> tcp6_ctlinput() casts a constant sockaddr_sin6 to non-const sockaddr.
> sa6_src may be &sa6_any which lives in read-only data section.
> 
> Better pass down the const addresses to tcp syn cache.  We only need
> them for lookup.

Oops, missed one satosin_const which breaks non-INET6 builds.

updated diff, ok?

bluhm

Index: netinet/tcp_input.c
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/netinet/tcp_input.c,v
diff -u -p -r1.398 tcp_input.c
--- netinet/tcp_input.c	11 Jan 2024 13:49:49 -0000	1.398
+++ netinet/tcp_input.c	19 Jan 2024 13:56:41 -0000
@@ -201,8 +201,8 @@ int	 syn_cache_add(struct sockaddr *, st
 struct socket *syn_cache_get(struct sockaddr *, struct sockaddr *,
 		struct tcphdr *, unsigned int, unsigned int, struct socket *,
 		struct mbuf *, uint64_t);
-struct syn_cache *syn_cache_lookup(struct sockaddr *, struct sockaddr *,
-		struct syn_cache_head **, u_int);
+struct syn_cache *syn_cache_lookup(const struct sockaddr *,
+		const struct sockaddr *, struct syn_cache_head **, u_int);
 
 /*
  * Insert segment ti into reassembly queue of tcp with
@@ -3109,9 +3109,9 @@ struct mutex syn_cache_mtx = MUTEX_INITI
 #ifndef INET6
 #define	SYN_HASHALL(hash, src, dst, rand) \
 do {									\
-	hash = SYN_HASH(&satosin(src)->sin_addr,			\
-		satosin(src)->sin_port,					\
-		satosin(dst)->sin_port, (rand));			\
+	hash = SYN_HASH(&satosin_const(src)->sin_addr,			\
+		satosin_const(src)->sin_port,				\
+		satosin_const(dst)->sin_port, (rand));			\
 } while (/*CONSTCOND*/ 0)
 #else
 #define SYN_HASH6(sa, sp, dp, rand) \
@@ -3125,14 +3125,14 @@ do {									\
 do {									\
 	switch ((src)->sa_family) {					\
 	case AF_INET:							\
-		hash = SYN_HASH(&satosin(src)->sin_addr,		\
-			satosin(src)->sin_port,				\
-			satosin(dst)->sin_port, (rand));		\
+		hash = SYN_HASH(&satosin_const(src)->sin_addr,		\
+			satosin_const(src)->sin_port,			\
+			satosin_const(dst)->sin_port, (rand));		\
 		break;							\
 	case AF_INET6:							\
-		hash = SYN_HASH6(&satosin6(src)->sin6_addr,		\
-			satosin6(src)->sin6_port,			\
-			satosin6(dst)->sin6_port, (rand));		\
+		hash = SYN_HASH6(&satosin6_const(src)->sin6_addr,	\
+			satosin6_const(src)->sin6_port,			\
+			satosin6_const(dst)->sin6_port, (rand));	\
 		break;							\
 	default:							\
 		hash = 0;						\
@@ -3423,7 +3423,7 @@ syn_cache_cleanup(struct tcpcb *tp)
  * Find an entry in the syn cache.
  */
 struct syn_cache *
-syn_cache_lookup(struct sockaddr *src, struct sockaddr *dst,
+syn_cache_lookup(const struct sockaddr *src, const struct sockaddr *dst,
     struct syn_cache_head **headp, u_int rtableid)
 {
 	struct syn_cache_set *sets[2];
@@ -3709,8 +3709,8 @@ syn_cache_reset(struct sockaddr *src, st
 }
 
 void
-syn_cache_unreach(struct sockaddr *src, struct sockaddr *dst, struct tcphdr *th,
-    u_int rtableid)
+syn_cache_unreach(const struct sockaddr *src, const struct sockaddr *dst,
+    struct tcphdr *th, u_int rtableid)
 {
 	struct syn_cache *sc;
 	struct syn_cache_head *scp;
Index: netinet/tcp_subr.c
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/netinet/tcp_subr.c,v
diff -u -p -r1.195 tcp_subr.c
--- netinet/tcp_subr.c	11 Jan 2024 13:49:49 -0000	1.195
+++ netinet/tcp_subr.c	19 Jan 2024 13:37:29 -0000
@@ -698,8 +698,8 @@ tcp6_ctlinput(int cmd, struct sockaddr *
 		} else if (inet6ctlerrmap[cmd] == EHOSTUNREACH ||
 		    inet6ctlerrmap[cmd] == ENETUNREACH ||
 		    inet6ctlerrmap[cmd] == EHOSTDOWN)
-			syn_cache_unreach((struct sockaddr *)sa6_src,
-			    sa, &th, rdomain);
+			syn_cache_unreach(sin6tosa_const(sa6_src), sa, &th,
+			    rdomain);
 		in_pcbunref(inp);
 	} else {
 		in6_pcbnotify(&tcbtable, sa6, 0,
Index: netinet/tcp_var.h
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/netinet/tcp_var.h,v
diff -u -p -r1.174 tcp_var.h
--- netinet/tcp_var.h	11 Jan 2024 13:49:49 -0000	1.174
+++ netinet/tcp_var.h	19 Jan 2024 13:37:29 -0000
@@ -799,7 +799,7 @@ int	tcp_signature(struct tdb *, int, str
 #endif /* TCP_SIGNATURE */
 void     tcp_set_iss_tsm(struct tcpcb *);
 
-void	 syn_cache_unreach(struct sockaddr *, struct sockaddr *,
+void	 syn_cache_unreach(const struct sockaddr *, const struct sockaddr *,
 	   struct tcphdr *, u_int);
 void	 syn_cache_init(void);
 void	 syn_cache_cleanup(struct tcpcb *);
Index: netinet6/in6.h
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/netinet6/in6.h,v
diff -u -p -r1.111 in6.h
--- netinet6/in6.h	28 Nov 2023 13:23:20 -0000	1.111
+++ netinet6/in6.h	19 Jan 2024 13:37:29 -0000
@@ -459,6 +459,12 @@ sin6tosa(struct sockaddr_in6 *sin6)
 	return ((struct sockaddr *)(sin6));
 }
 
+static inline const struct sockaddr *
+sin6tosa_const(const struct sockaddr_in6 *sin6)
+{
+	return ((const struct sockaddr *)(sin6));
+}
+
 static inline struct in6_ifaddr *
 ifatoia6(struct ifaddr *ifa)
 {