host: Do some proper validation when parsing CIDR-style subnets

The previous code returned negative or too large values (e.g. /33 or /-1)
to the caller, which some would then use unchecked.  In particular the
attribute parser in the vici plugin would use it directly to generate a
subnet mask using shifts by `32 - mask`, which could trigger undefined
behavior.

Fixes: 65697c2734 ("Added a CIDR notation based host constructor")

src/libstrongswan/networking/host.c

@@ -17,6 +17,8 @@
  * for more details.
  */
 
+#include <errno.h>
+
 #include "host.h"
 
 #include <utils/debug.h>
@@ -571,8 +573,9 @@ bool host_create_from_range(char *string, host_t **from, host_t **to)
  */
 host_t *host_create_from_subnet(char *string, int *bits)
 {
-	char *pos, buf[64];
+	char *pos, *end, buf[64];
 	host_t *net;
+	long netbits;
 
 	pos = strchr(string, '/');
 	if (pos)
@@ -583,8 +586,24 @@ host_t *host_create_from_subnet(char *string, int *bits)
 		}
 		strncpy(buf, string, pos - string);
 		buf[pos - string] = '\0';
-		*bits = atoi(pos + 1);
+		errno = 0;
-		return host_create_from_string(buf, 0);
+		netbits = strtol(pos + 1, &end, 10);
+		if (errno || end == pos + 1 || *end || netbits < 0 || netbits > 128)
+		{
+			return NULL;
+		}
+		net = host_create_from_string(buf, 0);
+		if (!net)
+		{
+			return NULL;
+		}
+		if (net->get_family(net) == AF_INET && netbits > 32)
+		{
+			net->destroy(net);
+			return NULL;
+		}
+		*bits = netbits;
+		return net;
 	}
 	net = host_create_from_string(string, 0);
 	if (net)

src/libstrongswan/tests/suites/test_host.c

@@ -418,8 +418,12 @@ START_TEST(test_create_from_subnet_v4)
 	ck_assert_int_eq(bits, 24);
 	host->destroy(host);
 
-	host = host_create_from_subnet("foo.b.a.r", &bits);
+	ck_assert(!host_create_from_subnet("192.168.0.1/33", &bits));
-	ck_assert(host == NULL);
+	ck_assert(!host_create_from_subnet("192.168.0.1/-1", &bits));
+	ck_assert(!host_create_from_subnet("192.168.0.1/foo", &bits));
+	ck_assert(!host_create_from_subnet("192.168.0.1/32foo", &bits));
+
+	ck_assert(!host_create_from_subnet("foo.b.a.r", &bits));
 }
 END_TEST
 
@@ -443,8 +447,12 @@ START_TEST(test_create_from_subnet_v6)
 	ck_assert_int_eq(bits, 64);
 	host->destroy(host);
 
-	host = host_create_from_subnet("foo::bar", &bits);
+	ck_assert(!host_create_from_subnet("fec1::1/129", &bits));
-	ck_assert(host == NULL);
+	ck_assert(!host_create_from_subnet("fec1::1/-1", &bits));
+	ck_assert(!host_create_from_subnet("fec1::1/foo", &bits));
+	ck_assert(!host_create_from_subnet("fec1::1/128foo", &bits));
+
+	ck_assert(!host_create_from_subnet("foo::bar", &bits));
 }
 END_TEST