From 08d66239fa7fd434c9774d2ab8b899d2511fef16 Mon Sep 17 00:00:00 2001
From: sw1tchbl4d3 <sw1tchbl4d3@sw1tchbl4d3.com>
Date: Tue, 8 Mar 2022 16:42:43 +0100
Subject: [PATCH] Reduce memory access in runprog

Previously, we used a for loop to rearrange argv to omit the first
argument, the rdo call itself.
It's way smarter to just dereference the first argv argument, and use it
as an argv pointer, to achieve the same result.
---
 rdo.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/rdo.c b/rdo.c
index 8bbb9e4..0937f82 100644
--- a/rdo.c
+++ b/rdo.c
@@ -33,19 +33,16 @@ void getconf(FILE* fp, const char* entry, char* result, size_t len_result) {
 	errx(1, "Could not get '%s' entry in config", entry);
 }
 
-int runprog(int argc, char** argv) {
-	for(int i=0; i<argc; i++)
-		argv[i] = argv[i + 1];
-
+void runprog(char** program_argv) {
 	if (setuid(0) < 0)
 		err(1, "Could not setuid");
 	if (setgid(0) < 0)
 		err(1, "Could not setgid");
 
-	if (execvp(argv[0], argv) != 0)
-		perror(argv[0]);
+	 // NOTE: this does not return when no error occurred.
+	execvp(program_argv[0], program_argv);
 
-	return 0;
+	err(1, program_argv[0]);
 }
 
 int main(int argc, char** argv) {
@@ -63,7 +60,7 @@ int main(int argc, char** argv) {
 
 	int ruid = getuid();
 	if (ruid == 0)
-		return runprog(argc, argv);
+		runprog(&argv[1]);
 
 	FILE* fp = fopen("/etc/rdo.conf", "r");
 
@@ -79,7 +76,7 @@ int main(int argc, char** argv) {
 	fclose(fp);
 
 	if (getsession(getppid(), ts_ttl) == 0)
-		return runprog(argc, argv);
+		runprog(&argv[1]);
 
 	struct passwd* p = getpwnam(username);
 	if (!p) {
@@ -111,7 +108,7 @@ int main(int argc, char** argv) {
 
 		if (strcmp(shadowEntry->sp_pwdp, hashed_pw) == 0) {
 			setsession(getppid(), ts_ttl);
-			return runprog(argc, argv);
+			runprog(&argv[1]);
 		}
 
 		usleep(sleep_ms);