1 files changed, 15 insertions, 5 deletions
diff --git a/src/shared/in-addr-util.c b/src/shared/in-addr-util.c
index 9dc9ec82b4..b02e7516ca 100644
--- a/src/shared/in-addr-util.c
+++ b/src/shared/in-addr-util.c
@@ -243,12 +243,25 @@ int in_addr_from_string_auto(const char *s, int *family, union in_addr_union *re
         return -EINVAL;
 }
 
-unsigned in_addr_netmask_to_prefixlen(const struct in_addr *addr) {
+unsigned char in_addr_netmask_to_prefixlen(const struct in_addr *addr) {
         assert(addr);
 
         return 32 - u32ctz(be32toh(addr->s_addr));
 }
 
+struct in_addr* in_addr_prefixlen_to_netmask(struct in_addr *addr, unsigned char prefixlen) {
+        assert(addr);
+        assert(prefixlen <= 32);
+
+        /* Shifting beyond 32 is not defined, handle this specially. */
+        if (prefixlen == 0)
+                addr->s_addr = 0;
+        else
+                addr->s_addr = htobe32((0xffffffff << (32 - prefixlen)) & 0xffffffff);
+
+        return addr;
+}
+
 int in_addr_default_prefixlen(const struct in_addr *addr, unsigned char *prefixlen) {
         uint8_t msb_octet = *(uint8_t*) addr;
 
@@ -284,9 +297,6 @@ int in_addr_default_subnet_mask(const struct in_addr *addr, struct in_addr *mask
         if (r < 0)
                 return r;
 
-        assert(prefixlen > 0 && prefixlen < 32);
-
-        mask->s_addr = htobe32((0xffffffff << (32 - prefixlen)) & 0xffffffff);
-
+        in_addr_prefixlen_to_netmask(mask, prefixlen);
         return 0;
 }