Re: resolvd: write nameservers in expected order

[Klemens Nanni]

On Sat, Nov 05, 2022 at 05:40:49AM -0600, Theo de Raadt wrote:
> +       if (mergesort(learning, ASR_MAXNS, sizeof(learning[0]), cmp) == -1)
> +               lerr(1, "mergesort");
> 
> So at runtime if mergesort() fails to allocate memory, the program will
> simply exit?

Ah no, that should just skip rebuilding the file, I think.


Index: resolvd.c
===================================================================
RCS file: /cvs/src/sbin/resolvd/resolvd.c,v
retrieving revision 1.28
diff -u -p -r1.28 resolvd.c
--- resolvd.c   2 Sep 2022 09:39:55 -0000       1.28
+++ resolvd.c   5 Nov 2022 11:48:22 -0000
@@ -503,17 +503,24 @@ handle_route_message(struct rt_msghdr *r
                return;
        }
 
-       /* Sort proposals, based upon priority and IP */
-       qsort(learning, ASR_MAXNS, sizeof(learning[0]), cmp);
+       /* Sort proposals, based upon priority */
+       if (mergesort(learning, ASR_MAXNS, sizeof(learning[0]), cmp) == -1) {
+               lwarn("mergesort");
+               return;
+       }
 
-       /* Eliminate duplicates */
+       /* Eliminate duplicate IPs per interface */
        for (i = 0; i < ASR_MAXNS - 1; i++) {
+               int j;
+
                if (learning[i].prio == 0)
                        continue;
-               if (learning[i].if_index == learning[i+1].if_index &&
-                   strcmp(learning[i].ip, learning[i+1].ip) == 0) {
-                       zeroslot(&learning[i + 1]);
-                       i--;    /* backup and re-check */
+
+               for (j = i + 1; j < ASR_MAXNS; j++) {
+                       if (learning[i].if_index == learning[j].if_index &&
+                           strcmp(learning[i].ip, learning[j].ip) == 0) {
+                               zeroslot(&learning[j]);
+                       }
                }
        }
 
@@ -694,10 +701,7 @@ cmp(const void *a, const void *b)
 {
        const struct rdns_proposal      *rpa = a, *rpb = b;
 
-       if (rpa->prio == rpb->prio)
-               return strcmp(rpa->ip, rpb->ip);
-       else
-               return rpa->prio < rpb->prio ? -1 : 1;
+       return (rpa->prio < rpb->prio) ? -1 : (rpa->prio > rpb->prio);
 }
 
 #ifndef SMALL