pkg/version: Prepare of extract-time oc version injection

Set a marker for oc to inject the release version to avoid potential
confusion from:

  $ oc adm release extract --command=openshift-install quay.io/openshift-release-dev/ocp-release:4.2.7
  $ ./openshift-install version
  ./openshift-install v4.2.5
  built from commit 425e4ff
  release image quay.io/openshift-release-dev/ocp-release@sha256:bac62983757570b9b8f8bc84c740782984a255c16372b3e30cfc8b52c0a187b9

The actual oc injection logic is in [1].

[1]: openshift/oc#165

cmd/openshift-install/log.go

@@ -67,7 +67,11 @@ func setupFileHook(baseDir string) func() {
 		DisableLevelTruncation: false,
 	}))
 
-	logrus.Debugf(version.String)
+	versionString, err := version.String()
+	if err != nil {
+		logrus.Fatal(err)
+	}
+	logrus.Debugf(versionString)
 	if version.Commit != "" {
 		logrus.Debugf("Built from commit %s", version.Commit)
 	}

cmd/openshift-install/version.go

@@ -21,7 +21,12 @@ func newVersionCmd() *cobra.Command {
 }
 
 func runVersionCmd(cmd *cobra.Command, args []string) error {
-	fmt.Printf("%s %s\n", os.Args[0], version.Raw)
+	versionString, err := version.Version()
+	if err != nil {
+		return err
+	}
+
+	fmt.Printf("%s %s\n", os.Args[0], versionString)
 	if version.Commit != "" {
 		fmt.Printf("built from commit %s\n", version.Commit)
 	}

pkg/asset/releaseimage/default.go

@@ -10,10 +10,10 @@ import (
 //
 // 1. Extract a release binary from the installer image referenced within the release image
 // 2. Identify the release image pull spec, add a NUL terminator byte (0x00) to the end, calculate length
-// 3. Length must be less than 300 bytes
+// 3. Length must be less than the marker length
 // 4. Search through the installer binary looking for `\x00_RELEASE_IMAGE_LOCATION_\x00<PADDING_TO_LENGTH>`
-//    where padding is the ASCII character X and length is the total length of the image
-// 5. Overwrite that chunk of the bytes if found, otherwise return error.
+//    where padding is the ASCII character X and length is the total length of the marker
+// 5. Overwrite the beginning of the marker with the release pullspec and a NUL terminator byte (0x00)
 //
 // On start the installer examines the constant and if it has been modified from the default the installer
 // will use that image.

pkg/version/version.go

@@ -1,18 +1,64 @@
 // Package version includes the version information for installer.
 package version
 
-import "fmt"
+import (
+	"fmt"
+	"strings"
+)
+
+// This file handles correctly identifying the default release version, which is expected to be
+// replaced in the binary post-compile by the release name extracted from a payload. The expected modification is:
+//
+// 1. Extract a release binary from the installer image referenced within the release image
+// 2. Identify the release name, add a NUL terminator byte (0x00) to the end, calculate length
+// 3. Length must be less than the marker length
+// 4. Search through the installer binary looking for `\x00_RELEASE_VERSION_LOCATION_\x00<PADDING_TO_LENGTH>`
+//    where padding is the ASCII character X and length is the total length of the marker
+// 5. Overwrite the beginning of the marker with the release name and a NUL terminator byte (0x00)
 
 var (
 	// Raw is the string representation of the version. This will be replaced
 	// with the calculated version at build time.
 	// set in hack/build.sh
 	Raw = "was not built correctly"
 
-	// String is the human-friendly representation of the version.
-	String = fmt.Sprintf("OpenShift Installer %s", Raw)
-
 	// Commit is the commit hash from which the installer was built.
 	// Set in hack/build.sh.
 	Commit = ""
+
+	// defaultReleaseInfoPadded may be replaced in the binary with Release Metadata: Version that overrides defaultVersion as
+	// a null-terminated string within the allowed character length. This allows a distributor to override the payload
+	// location without having to rebuild the source.
+	defaultVersionPadded = "\x00_RELEASE_VERSION_LOCATION_\x00XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\x00"
+	defaultVersionPrefix = "\x00_RELEASE_VERSION_LOCATION_\x00"
+	defaultVersionLength = len(defaultVersionPadded)
 )
+
+// String returns the human-friendly representation of the version.
+func String() (string, error) {
+	version, err := Version()
+	return fmt.Sprintf("OpenShift Installer %s", version), err
+}
+
+// Version returns the installer/release version.
+func Version() (string, error) {
+	if strings.HasPrefix(defaultVersionPadded, defaultVersionPrefix) {
+		return Raw, nil
+	}
+	nullTerminator := strings.IndexByte(defaultVersionPadded, '\x00')
+	if nullTerminator == -1 {
+		// the binary has been altered, but we didn't find a null terminator within the release name constant which is an error
+		return Raw, fmt.Errorf("release name location was replaced but without a null terminator before %d bytes", defaultVersionLength)
+	}
+	if nullTerminator > len(defaultVersionPadded) {
+		// the binary has been altered, but the null terminator is *longer* than the constant encoded in the binary
+		return Raw, fmt.Errorf("release name location contains no null-terminator and constant is corrupted")
+	}
+	releaseName := defaultVersionPadded[:nullTerminator]
+	if len(releaseName) == 0 {
+		// the binary has been altered, but the replaced release name is empty which is incorrect
+		// the oc binary will not be pinned to Release Metadata:Version
+		return Raw, fmt.Errorf("release name was incorrectly replaced during extract")
+	}
+	return releaseName, nil
+}