erl_interface: Avoid warnings about safe sprintf usage

In erl_interface there are three uses of `sprintf` to construct host
name strings. GCC 12 gives a `‘%s’ directive writing up to 254 bytes
into a region of size between 1 and 256` warning at these locations,
as it isn't smart enough to see that the manual bounds check is
correct and that the write is safe.

By switching to `snprintf` and removing the manual size calculation of
the resulting string, we can both simplify the relevant code and avoid
the warnings.

2 files changed, 6 insertions, 6 deletions

diff --git a/lib/erl_interface/src/connect/ei_connect.c b/lib/erl_interface/src/connect/ei_connect.c
index e5f1c307fd..3f2becde5a 100644
--- a/lib/erl_interface/src/connect/ei_connect.c
+++ b/lib/erl_interface/src/connect/ei_connect.c
@@ -1058,11 +1058,11 @@ int ei_connect_init_ussi(ei_cnode* ec, const char* this_node_name,
 	    strcpy(thishostname, hp->h_name);
 	}
     }
-    if (strlen(this_node_name) + 1 + strlen(thishostname) > MAXNODELEN) {
+    if (snprintf(thisnodename, sizeof(thisnodename), "%s@%s",
+                 this_node_name, thishostname) > sizeof(thisnodename)) {
         EI_TRACE_ERR0("ei_connect_init_ussi","this node name is too long");
         return ERL_ERROR;
     }
-    sprintf(thisnodename, "%s@%s", this_node_name, thishostname);
     res = ei_connect_xinit_ussi(ec, thishostname, thisalivename, thisnodename,
                                 (struct in_addr *)*hp->h_addr_list, cookie, creation,
                                 cbs, cbs_sz, setup_context);
diff --git a/lib/erl_interface/src/prog/erl_call.c b/lib/erl_interface/src/prog/erl_call.c
index 4548b9f4dd..1fb72c65cb 100644
--- a/lib/erl_interface/src/prog/erl_call.c
+++ b/lib/erl_interface/src/prog/erl_call.c
@@ -441,11 +441,11 @@ int main(int argc, char *argv[])
 
       memcpy(&h_ipadr.s_addr, *hp->h_addr_list, sizeof(struct in_addr));
       if (h_alivename) {
-          if (strlen(h_alivename) + strlen(h_hostname) + 2 > sizeof(h_nodename_buf)) {
+          if (snprintf(h_nodename_buf, sizeof(h_nodename_buf), "%s@%s",
+                       h_alivename, h_hostname) > sizeof(h_nodename_buf)) {;
               fprintf(stderr,"erl_call: hostname too long: %s\n", h_hostname);
               exit_free_flags_fields(1, &flags);
           }
-          sprintf(h_nodename, "%s@%s", h_alivename, h_hostname);
       }
       else {
           /* dynamic node name */
@@ -490,11 +490,11 @@ int main(int argc, char *argv[])
     }
 
     if (flags.port == -1) {
-        if (strlen(flags.node) + strlen(host_name) + 2 > sizeof(nodename)) {
+        if (snprintf(nodename, sizeof(nodename),
+                     "%s@%s", flags.node, host_name) > sizeof(nodename)) {
             fprintf(stderr,"erl_call: nodename too long: %s\n", flags.node);
             exit_free_flags_fields(1, &flags);
         }
-        sprintf(nodename, "%s@%s", flags.node, host_name);
     }
     /* 
      * Try to connect. Start an Erlang system if the