Replace magic number with constant DEVLIST_ALLOC_INITIAL_LEN & fix

memory leaks in calling `fido_dev_info_free`

* Add preprocessor constant `DEVLIST_ALLOC_INITIAL_LEN` to replace magic
number 64 in allocations of device info list. The named constant
expresses meaning and makes bugs & memory-leaks due to missed code
changes less likely, should one decide to change the number of slots to
allocate in the device info list.

* Fix the same errorneous code in freeing the device info list at three
points in the code:
Calling `fido_dev_info_free` with length argument `ndevs` deallocates
only the filled entries of the device info list, while leaving the empty
entries dangling. This does not seem to leak any data, though.
The commit fixes the code to actually deallocate the whole array.

pamu2fcfg/pamu2fcfg.c

@@ -467,13 +467,13 @@ int main(int argc, char *argv[]) {
   parse_args(argc, argv, &args);
   fido_init(args.debug ? FIDO_DEBUG : 0);
 
-  devlist = fido_dev_info_new(64);
+  devlist = fido_dev_info_new(DEVLIST_ALLOC_INITIAL_LEN);
   if (!devlist) {
     fprintf(stderr, "error: fido_dev_info_new failed\n");
     goto err;
   }
 
-  r = fido_dev_info_manifest(devlist, 64, &ndevs);
+  r = fido_dev_info_manifest(devlist, DEVLIST_ALLOC_INITIAL_LEN, &ndevs);
   if (r != FIDO_OK) {
     fprintf(stderr, "Unable to discover device(s), %s (%d)\n", fido_strerr(r),
             r);
@@ -489,7 +489,7 @@ int main(int argc, char *argv[]) {
       fflush(stderr);
       sleep(FREQUENCY);
 
-      r = fido_dev_info_manifest(devlist, 64, &ndevs);
+      r = fido_dev_info_manifest(devlist, DEVLIST_ALLOC_INITIAL_LEN, &ndevs);
       if (r != FIDO_OK) {
         fprintf(stderr, "\nUnable to discover device(s), %s (%d)",
                 fido_strerr(r), r);
@@ -564,7 +564,7 @@ int main(int argc, char *argv[]) {
 err:
   if (dev != NULL)
     fido_dev_close(dev);
-  fido_dev_info_free(&devlist, ndevs);
+  fido_dev_info_free(&devlist, DEVLIST_ALLOC_INITIAL_LEN);
   fido_cred_free(&cred);
   fido_dev_free(&dev);
 

util.c

@@ -1155,13 +1155,13 @@ int do_authentication(const cfg_t *cfg, const device_t *devices,
 #endif
   memset(&pk, 0, sizeof(pk));
 
-  devlist = fido_dev_info_new(64);
+  devlist = fido_dev_info_new(DEVLIST_ALLOC_INITIAL_LEN);
   if (!devlist) {
     debug_dbg(cfg, "Unable to allocate devlist");
     goto out;
   }
 
-  r = fido_dev_info_manifest(devlist, 64, &ndevs);
+  r = fido_dev_info_manifest(devlist, DEVLIST_ALLOC_INITIAL_LEN, &ndevs);
   if (r != FIDO_OK) {
     debug_dbg(cfg, "Unable to discover device(s), %s (%d)", fido_strerr(r), r);
     goto out;
@@ -1171,7 +1171,7 @@ int do_authentication(const cfg_t *cfg, const device_t *devices,
 
   debug_dbg(cfg, "Device max index is %zu", ndevs);
 
-  authlist = calloc(64 + 1, sizeof(fido_dev_t *));
+  authlist = calloc(DEVLIST_ALLOC_INITIAL_LEN + 1, sizeof(fido_dev_t *));
   if (!authlist) {
     debug_dbg(cfg, "Unable to allocate authenticator list");
     goto out;
@@ -1265,15 +1265,15 @@ int do_authentication(const cfg_t *cfg, const device_t *devices,
 
     i++;
 
-    fido_dev_info_free(&devlist, ndevs);
+    fido_dev_info_free(&devlist, DEVLIST_ALLOC_INITIAL_LEN);
 
-    devlist = fido_dev_info_new(64);
+    devlist = fido_dev_info_new(DEVLIST_ALLOC_INITIAL_LEN);
     if (!devlist) {
       debug_dbg(cfg, "Unable to allocate devlist");
       goto out;
     }
 
-    r = fido_dev_info_manifest(devlist, 64, &ndevs);
+    r = fido_dev_info_manifest(devlist, DEVLIST_ALLOC_INITIAL_LEN, &ndevs);
     if (r != FIDO_OK) {
       debug_dbg(cfg, "Unable to discover device(s), %s (%d)", fido_strerr(r),
                 r);
@@ -1299,7 +1299,7 @@ int do_authentication(const cfg_t *cfg, const device_t *devices,
 out:
   reset_pk(&pk);
   fido_assert_free(&assert);
-  fido_dev_info_free(&devlist, ndevs);
+  fido_dev_info_free(&devlist, DEVLIST_ALLOC_INITIAL_LEN);
 
   if (authlist) {
     for (size_t j = 0; authlist[j] != NULL; j++) {

util.h

@@ -21,6 +21,8 @@
 #define DEFAULT_ORIGIN_PREFIX "pam://"
 #define SSH_ORIGIN "ssh:"
 
+#define DEVLIST_ALLOC_INITIAL_LEN 64
+
 typedef struct {
   unsigned max_devs;
   int manual;