metalink: add some error checks

malloc() and strdup() calls without checking return codes.

Reported-by: Markus Elfring
Bug: https://github.com/bagder/curl/issues/150

src/tool_metalink.c

@@ -621,6 +621,8 @@ static int check_hash(const char *filename,
   }
 
   result = malloc(digest_def->dparams->digest_resultlen);
+  if(!result)
+    return -1;
   while(1) {
     unsigned char buf[4096];
     ssize_t len = read(fd, buf, sizeof(buf));
@@ -676,12 +678,17 @@ static metalink_checksum *new_metalink_checksum_from_hex_digest
   size_t i;
   size_t len = strlen(hex_digest);
   digest = malloc(len/2);
+  if(!digest)
+    return 0;
+
   for(i = 0; i < len; i += 2) {
     digest[i/2] = hex_to_uint(hex_digest+i);
   }
   chksum = malloc(sizeof(metalink_checksum));
-  chksum->digest_def = digest_def;
-  chksum->digest = digest;
+  if(chksum) {
+    chksum->digest_def = digest_def;
+    chksum->digest = digest;
+  }
   return chksum;
 }
 
@@ -689,8 +696,14 @@ static metalink_resource *new_metalink_resource(const char *url)
 {
   metalink_resource *res;
   res = malloc(sizeof(metalink_resource));
-  res->next = NULL;
-  res->url = strdup(url);
+  if(res) {
+    res->next = NULL;
+    res->url = strdup(url);
+    if(!res->url) {
+      free(res);
+      return NULL;
+    }
+  }
   return res;
 }
 
@@ -715,8 +728,15 @@ static metalinkfile *new_metalinkfile(metalink_file_t *fileinfo)
 {
   metalinkfile *f;
   f = (metalinkfile*)malloc(sizeof(metalinkfile));
+  if(!f)
+    return NULL;
+
   f->next = NULL;
   f->filename = strdup(fileinfo->name);
+  if(!f->filename) {
+    free(f);
+    return NULL;
+  }
   f->checksum = NULL;
   f->resource = NULL;
   if(fileinfo->checksums) {
@@ -817,8 +837,10 @@ int parse_metalink(struct OperationConfig *config, struct OutStruct *outs,
       url = new_getout(config);
 
     if(url) {
-      metalinkfile *mlfile;
-      mlfile = new_metalinkfile(*files);
+      metalinkfile *mlfile = new_metalinkfile(*files);
+      if(!mlfile)
+        break;
+
       if(!mlfile->checksum) {
         warnings = TRUE;
         fprintf(config->global->errors,