ipv4acd: rework how we pick ipv4ll addresses

Let's make the seed actually work as stable seed, and use siphash24 to generate
the series of addresses, instead of the opaque libc random_r().

This not only makes the seed truly work as stable, portable seed, but also
makes the code quite a bit shorter, and removes a couple of memory allocations.

1 files changed, 61 insertions, 70 deletions

diff --git a/src/libsystemd-network/sd-ipv4ll.c b/src/libsystemd-network/sd-ipv4ll.c
index 0e6a9df9e5..4fcb06a308 100644
--- a/src/libsystemd-network/sd-ipv4ll.c
+++ b/src/libsystemd-network/sd-ipv4ll.c
@@ -28,6 +28,7 @@
 #include "sd-ipv4ll.h"
 
 #include "alloc-util.h"
+#include "ether-addr-util.h"
 #include "in-addr-util.h"
 #include "list.h"
 #include "random-util.h"
@@ -35,8 +36,8 @@
 #include "sparse-endian.h"
 #include "util.h"
 
-#define IPV4LL_NETWORK 0xA9FE0000UL
-#define IPV4LL_NETMASK 0xFFFF0000UL
+#define IPV4LL_NETWORK UINT32_C(0xA9FE0000)
+#define IPV4LL_NETMASK UINT32_C(0xFFFF0000)
 
 #define IPV4LL_DONT_DESTROY(ll) \
         _cleanup_(sd_ipv4ll_unrefp) _unused_ sd_ipv4ll *_dont_destroy_##ll = sd_ipv4ll_ref(ll)
@@ -45,16 +46,25 @@ struct sd_ipv4ll {
         unsigned n_ref;
 
         sd_ipv4acd *acd;
+
         be32_t address; /* the address pushed to ACD */
-        struct random_data *random_data;
-        char *random_data_state;
+        struct ether_addr mac;
+
+        struct {
+                le64_t value;
+                le64_t generation;
+        } seed;
+        bool seed_set;
 
         /* External */
         be32_t claimed_address;
+
         sd_ipv4ll_callback_t callback;
         void* userdata;
 };
 
+static void ipv4ll_on_acd(sd_ipv4acd *ll, int event, void *userdata);
+
 sd_ipv4ll *sd_ipv4ll_ref(sd_ipv4ll *ll) {
         if (!ll)
                 return NULL;
@@ -76,16 +86,11 @@ sd_ipv4ll *sd_ipv4ll_unref(sd_ipv4ll *ll) {
                 return NULL;
 
         sd_ipv4acd_unref(ll->acd);
-
-        free(ll->random_data);
-        free(ll->random_data_state);
         free(ll);
 
         return NULL;
 }
 
-static void ipv4ll_on_acd(sd_ipv4acd *ll, int event, void *userdata);
-
 int sd_ipv4ll_new(sd_ipv4ll **ret) {
         _cleanup_(sd_ipv4ll_unrefp) sd_ipv4ll *ll = NULL;
         int r;
@@ -113,43 +118,32 @@ int sd_ipv4ll_new(sd_ipv4ll **ret) {
 }
 
 int sd_ipv4ll_stop(sd_ipv4ll *ll) {
-        int r;
-
         assert_return(ll, -EINVAL);
 
-        r = sd_ipv4acd_stop(ll->acd);
-        if (r < 0)
-                return r;
-
-        return 0;
+        return sd_ipv4acd_stop(ll->acd);
 }
 
 int sd_ipv4ll_set_ifindex(sd_ipv4ll *ll, int ifindex) {
         assert_return(ll, -EINVAL);
         assert_return(ifindex > 0, -EINVAL);
+        assert_return(sd_ipv4ll_is_running(ll) == 0, -EBUSY);
 
         return sd_ipv4acd_set_ifindex(ll->acd, ifindex);
 }
 
-#define HASH_KEY SD_ID128_MAKE(df,04,22,98,3f,ad,14,52,f9,87,2e,d1,9c,70,e2,f2)
-
 int sd_ipv4ll_set_mac(sd_ipv4ll *ll, const struct ether_addr *addr) {
         int r;
 
         assert_return(ll, -EINVAL);
+        assert_return(addr, -EINVAL);
+        assert_return(sd_ipv4ll_is_running(ll) == 0, -EBUSY);
 
-        if (!ll->random_data) {
-                uint64_t seed;
-
-                /* If no random data is set, generate some from the MAC */
-                seed = siphash24(&addr->ether_addr_octet, ETH_ALEN, HASH_KEY.bytes);
-
-                r = sd_ipv4ll_set_address_seed(ll, htole64(seed));
-                if (r < 0)
-                        return r;
-        }
+        r = sd_ipv4acd_set_mac(ll->acd, addr);
+        if (r < 0)
+                return r;
 
-        return sd_ipv4acd_set_mac(ll->acd, addr);
+        ll->mac = *addr;
+        return 0;
 }
 
 int sd_ipv4ll_detach_event(sd_ipv4ll *ll) {
@@ -186,31 +180,11 @@ int sd_ipv4ll_get_address(sd_ipv4ll *ll, struct in_addr *address) {
 }
 
 int sd_ipv4ll_set_address_seed(sd_ipv4ll *ll, uint64_t seed) {
-        _cleanup_free_ struct random_data *random_data = NULL;
-        _cleanup_free_ char *random_data_state = NULL;
-        int r;
-
         assert_return(ll, -EINVAL);
+        assert_return(sd_ipv4ll_is_running(ll) == 0, -EBUSY);
 
-        random_data = new0(struct random_data, 1);
-        if (!random_data)
-                return -ENOMEM;
-
-        random_data_state = new0(char, 128);
-        if (!random_data_state)
-                return -ENOMEM;
-
-        r = initstate_r((unsigned) seed, random_data_state, 128, random_data);
-        if (r < 0)
-                return r;
-
-        free(ll->random_data);
-        ll->random_data = random_data;
-        random_data = NULL;
-
-        free(ll->random_data_state);
-        ll->random_data_state = random_data_state;
-        random_data_state = NULL;
+        ll->seed.value = htole64(seed);
+        ll->seed_set = true;
 
         return 0;
 }
@@ -254,48 +228,64 @@ int sd_ipv4ll_set_address(sd_ipv4ll *ll, const struct in_addr *address) {
         return 0;
 }
 
+#define PICK_HASH_KEY SD_ID128_MAKE(15,ac,82,a6,d6,3f,49,78,98,77,5d,0c,69,02,94,0b)
+
 static int ipv4ll_pick_address(sd_ipv4ll *ll) {
-        struct in_addr in_addr;
         be32_t addr;
-        int r;
-        int32_t random;
 
         assert(ll);
-        assert(ll->random_data);
 
         do {
-                r = random_r(ll->random_data, &random);
-                if (r < 0)
-                        return r;
-                addr = htobe32((random & 0x0000FFFF) | IPV4LL_NETWORK);
-        } while (addr == ll->address ||
-                (ntohl(addr) & 0x0000FF00) == 0x0000 ||
-                (ntohl(addr) & 0x0000FF00) == 0xFF00);
+                uint64_t h;
 
-        in_addr.s_addr = addr;
+                h = siphash24(&ll->seed, sizeof(ll->seed), PICK_HASH_KEY.bytes);
 
-        r = sd_ipv4ll_set_address(ll, &in_addr);
-        if (r < 0)
-                return r;
+                /* Increase the generation counter by one */
+                ll->seed.generation = htole64(le64toh(ll->seed.generation) + 1);
 
-        return 0;
+                addr = htobe32((h & UINT32_C(0x0000FFFF)) | IPV4LL_NETWORK);
+        } while (addr == ll->address ||
+                (be32toh(addr) & 0x0000FF00) == 0x0000 ||
+                (be32toh(addr) & 0x0000FF00) == 0xFF00);
+
+        return sd_ipv4ll_set_address(ll, &(struct in_addr) { addr });
 }
 
+#define MAC_HASH_KEY SD_ID128_MAKE(df,04,22,98,3f,ad,14,52,f9,87,2e,d1,9c,70,e2,f2)
+
 int sd_ipv4ll_start(sd_ipv4ll *ll) {
         int r;
+        bool picked_address = false;
 
         assert_return(ll, -EINVAL);
-        assert_return(ll->random_data, -EINVAL);
+        assert_return(!ether_addr_is_null(&ll->mac), -EINVAL);
+        assert_return(sd_ipv4ll_is_running(ll) == 0, -EBUSY);
+
+        /* If no random seed is set, generate some from the MAC address */
+        if (!ll->seed_set)
+                ll->seed.value = htole64(siphash24(ll->mac.ether_addr_octet, ETH_ALEN, MAC_HASH_KEY.bytes));
+
+        /* Restart the generation counter. */
+        ll->seed.generation = 0;
 
         if (ll->address == 0) {
                 r = ipv4ll_pick_address(ll);
                 if (r < 0)
                         return r;
+
+                picked_address = true;
         }
 
         r = sd_ipv4acd_start(ll->acd);
-        if (r < 0)
+        if (r < 0) {
+
+                /* We couldn't start? If so, let's forget the picked address again, the user might make a change and
+                 * retry, and we want the new data to take effect when picking an address. */
+                if (picked_address)
+                        ll->address = 0;
+
                 return r;
+        }
 
         return 0;
 }
@@ -345,6 +335,7 @@ void ipv4ll_on_acd(sd_ipv4acd *acd, int event, void *userdata) {
                 }
 
                 break;
+
         default:
                 assert_not_reached("Invalid IPv4ACD event.");
         }