rc_exec: allow setting child's uid and gid

Author: N-R-K

src/shared/rc_exec.c

@@ -44,6 +44,8 @@ struct exec_args exec_init(const char **argv)
 	args.redirect_stdin  = EXEC_NO_REDIRECT;
 	args.redirect_stdout = EXEC_NO_REDIRECT;
 	args.redirect_stderr = EXEC_NO_REDIRECT;
+	args.uid = (uid_t)-1;
+	args.gid = (gid_t)-1;
 	return args;
 }
 
@@ -100,6 +102,10 @@ struct exec_result do_exec(struct exec_args *args)
 		if (args->redirect_stderr != EXEC_NO_REDIRECT &&
 		    dup2(args->redirect_stderr, STDERR_FILENO) < 0)
 			goto child_err;
+		if (args->gid != (gid_t)-1 && setgid(args->gid) < 0)
+			goto child_err;
+		if (args->uid != (uid_t)-1 && setuid(args->uid) < 0)
+			goto child_err;
 		if (args->setsid && setsid() < 0)
 			goto child_err;
 		sigprocmask(SIG_SETMASK, &old, NULL);

src/shared/rc_exec.h

@@ -36,6 +36,8 @@ struct exec_args {
 	int redirect_stdin;
 	int redirect_stdout;
 	int redirect_stderr;
+	uid_t uid;
+	gid_t gid;
 	bool setsid : 1;
 };