conf, fwd: Check forwarding table for conflicting rules

It's possible for a user to supply conflicting forwarding parameters, e.g.
    $ pasta -t 80:8080 -t 127.0.0.1/80:8888

We give a warning in this case, but it's based on the legacy
forwarding bitmaps.  This is too strict, because it will also warn on
cases that shouldn't conflict because they use different addresses,
e.g.
    $ pasta -t 192.0.2.1/80:8080 127.0.0.1/80:8888

Theoretically, it's also too loose because it won't take into account
auto-scan forwarding rules.  We can't hit that in practice now,
because we only ever have one auto-scan rule and nothing else, but we
want to remove that restriction in future.

Replace the bitmap based check with a check based on actually scanning
the forwarding rules for conflicts.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

4 files changed, 40 insertions, 6 deletions

diff --git a/conf.c b/conf.c
index ce6c012..2f22a7f 100644
--- a/conf.c
+++ b/conf.c
@@ -172,11 +172,6 @@ static void conf_ports_range_except(const struct ctx *c, char optname,
 		for (i = base; i <= last; i++) {
 			if (exclude && bitmap_isset(exclude, i))
 				break;
-
-			if (bitmap_isset(fwd->map, i)) {
-				warn(
-"Altering mapping of already mapped port number: %s", optarg);
-			}
 		}
 
 		if ((optname == 'T' || optname == 'U') && c->no_bindtodevice) {
diff --git a/fwd.c b/fwd.c
index 50df3d5..bc2698f 100644
--- a/fwd.c
+++ b/fwd.c
@@ -349,7 +349,7 @@ void fwd_rule_add(struct fwd_ports *fwd, uint8_t flags,
 	const uint8_t allowed_flags = FWD_WEAK | FWD_SCAN;
 	unsigned num = (unsigned)last - first + 1;
 	struct fwd_rule *new;
-	unsigned port;
+	unsigned i, port;
 
 	ASSERT(!(flags & ~allowed_flags));
 
@@ -358,6 +358,25 @@ void fwd_rule_add(struct fwd_ports *fwd, uint8_t flags,
 	if ((fwd->sock_count + num) > ARRAY_SIZE(fwd->socks))
 		die("Too many listening sockets");
 
+	/* Check for any conflicting entries */
+	for (i = 0; i < fwd->count; i++) {
+		char newstr[INANY_ADDRSTRLEN], rulestr[INANY_ADDRSTRLEN];
+		struct fwd_rule *rule = &fwd->rules[i];
+
+		if (!inany_matches(addr, fwd_rule_addr(rule)))
+			/* Non-conflicting addresses */
+			continue;
+
+		if (last < rule->first || rule->last < first)
+			/* Port ranges don't overlap */
+			continue;
+
+		die("Forwarding configuration conflict: %s/%u-%u versus %s/%u-%u",
+		    inany_ntop(addr, newstr, sizeof(newstr)), first, last,
+		    inany_ntop(fwd_rule_addr(rule), rulestr, sizeof(rulestr)),
+		    rule->first, rule->last);
+	}
+
 	new = &fwd->rules[fwd->count++];
 	new->flags = flags;
 
diff --git a/inany.c b/inany.c
index 87a4d8b..543b60d 100644
--- a/inany.c
+++ b/inany.c
@@ -21,6 +21,25 @@
 const union inany_addr inany_loopback4 = INANY_INIT4(IN4ADDR_LOOPBACK_INIT);
 const union inany_addr inany_any4 = INANY_INIT4(IN4ADDR_ANY_INIT);
 
+/** inany_matches - Do two addresses match?
+ * @a, @b:	IPv[46] addresses (NULL for 0.0.0.0 & ::)
+ *
+ * Return: true if they match, false otherwise
+ *
+ * Addresses match themselves, but also unspecified addresses of the same
+ * family.
+ */
+bool inany_matches(const union inany_addr *a, const union inany_addr *b)
+{
+	if (!a || !b)
+		return true;
+
+	if (inany_is_unspecified(a) || inany_is_unspecified(b))
+		return !!inany_v4(a) == !!inany_v4(b);
+
+	return inany_equals(a, b);
+}
+
 /** inany_ntop - Convert an IPv[46] address to text format
  * @src:	IPv[46] address (NULL for unspecified)
  * @dst:	output buffer, minimum INANY_ADDRSTRLEN bytes
diff --git a/inany.h b/inany.h
index 61b36fb..b02c289 100644
--- a/inany.h
+++ b/inany.h
@@ -293,6 +293,7 @@ static inline void inany_siphash_feed(struct siphash_state *state,
 
 #define INANY_ADDRSTRLEN	MAX(INET_ADDRSTRLEN, INET6_ADDRSTRLEN)
 
+bool inany_matches(const union inany_addr *a, const union inany_addr *b);
 const char *inany_ntop(const union inany_addr *src, char *dst, socklen_t size);
 int inany_pton(const char *src, union inany_addr *dst);