Use container's environment when starting the init process (#329)

Fixes an issue first described in
https://github.com/apple/container/issues/740.

Previously the initial process of the container was using vminitd's
environment variables to find the target executable. This PR updates the
code to use the container's configured environment for the initial
process instead. The behavior of an exec in a container should be the
same as before.

Signed-off-by: Kathryn Baldauf <k_baldauf@apple.com>

Sources/ContainerizationOS/Path.swift

@@ -21,14 +21,18 @@ import Foundation
 public struct Path {
     /// lookPath looks up an executable's path from $PATH
     public static func lookPath(_ name: String) -> URL? {
-        lookup(name, path: getPath())
+        lookup(name, path: getCurrentPath())
+    }
+
+    public static func lookPath(_ name: String, path: String) -> URL? {
+        lookup(name, path: path)
     }
 
     // getEnv returns the default environment of the process
     // with the default $PATH added for the context of a macOS application bundle
     public static func getEnv() -> [String: String] {
         var env = ProcessInfo.processInfo.environment
-        env["PATH"] = getPath()
+        env["PATH"] = getCurrentPath()
         return env
     }
 
@@ -58,14 +62,17 @@ public struct Path {
     }
 
     /// getPath returns $PATH for the current process
-    private static func getPath() -> String {
+    public static func getCurrentPath() -> String {
         let env = ProcessInfo.processInfo.environment
         return env["PATH"] ?? "/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin"
     }
 
     // findPath returns a string containing the 'PATH' environment variable
-    private static func findPath(_ env: [String]) -> String? {
-        env.first(where: { path in
+    public static func findPath(_ env: [String]?) -> String? {
+        guard let env = env else {
+            return nil
+        }
+        return env.first(where: { path in
             let split = path.split(separator: "=")
             return split.count == 2 && split[0] == "PATH"
         })

vminitd/Sources/vmexec/RunCommand.swift

@@ -138,7 +138,7 @@ struct RunCommand: ParsableCommand {
         try App.setPermissions(user: process.user)
 
         // Finally execve the container process.
-        try App.exec(process: process)
+        try App.exec(process: process, currentEnv: process.env)
     }
 
     private func execInNamespace(spec: ContainerizationOCI.Spec, log: Logger) throws {

vminitd/Sources/vmexec/vmexec.swift

@@ -22,6 +22,7 @@
 import ArgumentParser
 import ContainerizationError
 import ContainerizationOCI
+import ContainerizationOS
 import Foundation
 import LCShim
 import Logging
@@ -71,8 +72,14 @@ extension App {
         }
     }
 
-    static func exec(process: ContainerizationOCI.Process) throws {
-        let executable = strdup(process.args[0])
+    static func exec(process: ContainerizationOCI.Process, currentEnv: [String]? = nil) throws {
+        // lookup executable
+        let path = Path.findPath(currentEnv) ?? Path.getCurrentPath()
+        guard let resolvedExecutable = Path.lookPath(process.args[0], path: path) else {
+            throw App.Failure(message: "Failed to find target executable \(process.args[0])")
+        }
+
+        let executable = strdup(resolvedExecutable.path())
         var argv = process.args.map { strdup($0) }
         argv += [nil]