interfaces: fix out-of-bound access when getting permanent MAC address

Also, use a classic malloc() instead of a weird union. This makes
compilers better to catch this kind of error (at least on runtime with
sanitizers).

diff --git a/src/daemon/interfaces-linux.c b/src/daemon/interfaces-linux.c
index 38b61f8b2c93b252a61138d9e145ee6d69696acf..700626e3e3c0f5a385e0d06acd10666ccf7798ca 100644 (file)
--- a/src/daemon/interfaces-linux.c
+++ b/src/daemon/interfaces-linux.c
@@ -288,17 +288,15 @@ iflinux_get_permanent_mac_ethtool(struct lldpd *cfg,
     struct interfaces_device_list *interfaces,
     struct interfaces_device *iface)
 {
+       int ret = -1;
        struct ifreq ifr = {};
-       union {
-               struct ethtool_perm_addr addr;
-               /* cppcheck-suppress unusedStructMember */
-               char u8[sizeof(struct ethtool_perm_addr) + ETHER_ADDR_LEN];
-       } epaddr;
+       struct ethtool_perm_addr *epaddr = calloc(sizeof(struct ethtool_perm_addr) + ETHER_ADDR_LEN, 1);
+       if (epaddr == NULL) goto end;
 
        strlcpy(ifr.ifr_name, iface->name, sizeof(ifr.ifr_name));
-       epaddr.addr.cmd = ETHTOOL_GPERMADDR;
-       epaddr.addr.size = ETHER_ADDR_LEN;
-       ifr.ifr_data = (caddr_t)&epaddr.addr;
+       epaddr->cmd = ETHTOOL_GPERMADDR;
+       epaddr->size = ETHER_ADDR_LEN;
+       ifr.ifr_data = (caddr_t)epaddr;
        if (ioctl(cfg->g_sock, SIOCETHTOOL, &ifr) == -1) {
                static int once = 0;
                if (errno == EPERM && !once) {
@@ -306,25 +304,27 @@ iflinux_get_permanent_mac_ethtool(struct lldpd *cfg,
                            "no permission to get permanent MAC address for %s (requires 2.6.19+)",
                            iface->name);
                        once = 1;
-                       return -1;
+                       goto end;
                }
                if (errno != EPERM)
                        log_warn("interfaces", "cannot get permanent MAC address for %s",
                            iface->name);
-               return -1;
+               goto end;
        }
-       if (epaddr.addr.data[0] != 0 ||
-           epaddr.addr.data[1] != 0 ||
-           epaddr.addr.data[2] != 0 ||
-           epaddr.addr.data[3] != 0 ||
-           epaddr.addr.data[4] != 0 ||
-           epaddr.addr.data[5] != 0 ||
-           epaddr.addr.data[6] != 0) {
-               memcpy(iface->address, epaddr.addr.data, ETHER_ADDR_LEN);
-               return 0;
+       if (epaddr->data[0] != 0 ||
+           epaddr->data[1] != 0 ||
+           epaddr->data[2] != 0 ||
+           epaddr->data[3] != 0 ||
+           epaddr->data[4] != 0 ||
+           epaddr->data[5] != 0) {
+               memcpy(iface->address, epaddr->data, ETHER_ADDR_LEN);
+               ret = 0;
+               goto end;
        }
        log_debug("interfaces", "cannot get permanent MAC for %s (all 0)", iface->name);
-       return -1;
+ end:
+       free(epaddr);
+       return ret;
 }
 
 /**