3 files changed, 54 insertions, 15 deletions

diff --git a/src/libsystemd-network/sd-dhcp-lease.c b/src/libsystemd-network/sd-dhcp-lease.c
index 6680d06736..4fb01c0729 100644
--- a/src/libsystemd-network/sd-dhcp-lease.c
+++ b/src/libsystemd-network/sd-dhcp-lease.c
@@ -30,6 +30,7 @@
 #include "list.h"
 #include "mkdir.h"
 #include "fileio.h"
+#include "in-addr-util.h"
 
 #include "dhcp-protocol.h"
 #include "dhcp-internal.h"
@@ -803,27 +804,20 @@ int dhcp_lease_load(const char *lease_file, sd_dhcp_lease **ret) {
 }
 
 int dhcp_lease_set_default_subnet_mask(sd_dhcp_lease *lease) {
-        uint32_t address;
+        struct in_addr address;
+        struct in_addr mask;
+        int r;
 
         assert(lease);
-        assert(lease->address != INADDR_ANY);
 
-        address = be32toh(lease->address);
+        address.s_addr = lease->address;
 
         /* fall back to the default subnet masks based on address class */
+        r = in_addr_default_subnet_mask(&address, &mask);
+        if (r < 0)
+                return r;
 
-        if ((address >> 31) == 0x0)
-                /* class A, leading bits: 0 */
-                lease->subnet_mask = htobe32(0xff000000);
-        else if ((address >> 30) == 0x2)
-                /* class B, leading bits 10 */
-                lease->subnet_mask = htobe32(0xffff0000);
-        else if ((address >> 29) == 0x6)
-                /* class C, leading bits 110 */
-                lease->subnet_mask = htobe32(0xffffff00);
-        else
-                /* class D or E, no default mask. give up */
-                return -ERANGE;
+        lease->subnet_mask = mask.s_addr;
 
         return 0;
 }
diff --git a/src/shared/in-addr-util.c b/src/shared/in-addr-util.c
index 457eedd6d8..5fbee6caf2 100644
--- a/src/shared/in-addr-util.c
+++ b/src/shared/in-addr-util.c
@@ -248,3 +248,46 @@ unsigned in_addr_netmask_to_prefixlen(const struct in_addr *addr) {
 
         return 32 - u32ctz(be32toh(addr->s_addr));
 }
+
+int in_addr_default_prefixlen(const struct in_addr *addr, unsigned char *prefixlen) {
+        uint32_t address;
+
+        assert(addr);
+        assert(addr->s_addr != INADDR_ANY);
+        assert(prefixlen);
+
+        address = be32toh(addr->s_addr);
+
+        if ((address >> 31) == 0x0)
+                /* class A, leading bits: 0 */
+                *prefixlen = 8;
+        else if ((address >> 30) == 0x2)
+                /* class B, leading bits 10 */
+                *prefixlen = 16;
+        else if ((address >> 29) == 0x6)
+                /* class C, leading bits 110 */
+                *prefixlen = 24;
+        else
+                /* class D or E, no default prefixlen */
+                return -ERANGE;
+
+        return 0;
+}
+
+int in_addr_default_subnet_mask(const struct in_addr *addr, struct in_addr *mask) {
+        unsigned char prefixlen;
+        int r;
+
+        assert(addr);
+        assert(mask);
+
+        r = in_addr_default_prefixlen(addr, &prefixlen);
+        if (r < 0)
+                return r;
+
+        assert(prefixlen > 0 && prefixlen < 32);
+
+        mask->s_addr = htobe32((0xffffffff << (32 - prefixlen)) & 0xffffffff);
+
+        return 0;
+}
diff --git a/src/shared/in-addr-util.h b/src/shared/in-addr-util.h
index 0036acee22..8da030ceb6 100644
--- a/src/shared/in-addr-util.h
+++ b/src/shared/in-addr-util.h
@@ -40,6 +40,8 @@ int in_addr_to_string(int family, const union in_addr_union *u, char **ret);
 int in_addr_from_string(int family, const char *s, union in_addr_union *ret);
 int in_addr_from_string_auto(const char *s, int *family, union in_addr_union *ret);
 unsigned in_addr_netmask_to_prefixlen(const struct in_addr *addr);
+int in_addr_default_prefixlen(const struct in_addr *addr, unsigned char *prefixlen);
+int in_addr_default_subnet_mask(const struct in_addr *addr, struct in_addr *mask);
 
 static inline size_t FAMILY_ADDRESS_SIZE(int family) {
         assert(family == AF_INET || family == AF_INET6);