common: validate iso_file input

builder/proxmox/common/config.go

@@ -678,6 +678,11 @@ func (c *Config) Prepare(upper interface{}, raws ...interface{}) ([]string, []st
 		// (possibly to a local file) to an ISO file that will be downloaded and
 		// then uploaded to Proxmox.
 		if c.ISOs[idx].ISOFile != "" {
+			// ISOFile should match <storage>:iso/<ISO filename> format
+			res := regexp.MustCompile(`^.+:iso\/.+$`)
+			if !res.MatchString(c.ISOs[idx].ISOFile) {
+				errs = packersdk.MultiErrorAppend(errs, fmt.Errorf("iso_path should match pattern \"<storage>:iso/<ISO filename>\". Provided value was \"%s\"", c.ISOs[idx].ISOFile))
+			}
 			c.ISOs[idx].ShouldUploadISO = false
 		} else {
 			c.ISOs[idx].DownloadPathKey = "downloaded_additional_iso_path_" + strconv.Itoa(idx)

builder/proxmox/common/config_test.go

@@ -151,6 +151,17 @@ func TestISOs(t *testing.T) {
 				"type": "ide",
 			},
 		},
+		{
+			name:           "iso_file should fail if not correct format",
+			expectedToFail: true,
+			ISOs: map[string]interface{}{
+				"type": "ide",
+				"cd_files": []string{
+					"config_test.go",
+				},
+				"iso_file": "local:/test.iso",
+			},
+		},
 		{
 			name:           "cd_files and iso_file specified should fail",
 			expectedToFail: true,