From c1050a27f94f685c9a3480dcab98f74c1f1cc4ef Mon Sep 17 00:00:00 2001
From: Alessandro Mauri <alemauri001@gmail.com>
Date: Sun, 11 Jul 2021 13:35:36 +0200
Subject: [PATCH] added erroring functions

---
 us.c | 60 +++++++++++++++++++++++++++++++++---------------------------
 1 file changed, 33 insertions(+), 27 deletions(-)

diff --git a/us.c b/us.c
index 4ee68d9..5ae34a6 100644
--- a/us.c
+++ b/us.c
@@ -47,6 +47,8 @@
 
 #define MAX_HASH 1024
 
+static void *emalloc(size_t);
+static char *estrdup(const char *);
 static void usage(void);
 static void die(const char *, ...);
 static int perm_set(struct passwd *, struct group *);
@@ -102,9 +104,11 @@ int main(int argc, char *argv[])
 		fprintf(stderr, "getpwid: %s\n", strerror(errno));
 		return errno;
 	}
-	char *my_name = strdup(my_pw->pw_name);
-	if (!my_name)
-		die("strdup:");
+	char *my_name = estrdup(my_pw->pw_name);
+
+	/* From now on most actions require root */
+	if (setuid(0) == -1)
+		die("setuid:");
 
 	/* Authenticate, we will be root from now on */
 	if (authenticate(my_pw->pw_uid, 0))
@@ -128,22 +132,13 @@ int main(int argc, char *argv[])
 	int c_argc = argc - optind;
 	char **c_argv;
 	if (c_argc) {
-		c_argv = malloc(sizeof(char *) * (c_argc + 1));
-		if (!c_argv)
-			die("malloc:");
-		for (int i = 0; optind < argc; optind++, i++) {
-			c_argv[i] = strdup(argv[optind]);
-			if (!c_argv[i])
-				die("strdup:");
-		}
+		c_argv = emalloc(sizeof(char *) * (c_argc + 1));
+		for (int i = 0; optind < argc; optind++, i++)
+			c_argv[i] = estrdup(argv[optind]);
 	} else {
 		c_argc = 1;
-		c_argv = malloc(sizeof(char *) * (c_argc + 1));
-		if (!c_argv)
-			die("malloc:");
-		c_argv[0] = strdup(shell);
-		if (!c_argv[0])
-			die("strdup:");
+		c_argv = emalloc(sizeof(char *) * (c_argc + 1));
+		c_argv[0] = estrdup(shell);
 	}
 	c_argv[c_argc] = NULL;
 
@@ -171,11 +166,8 @@ int main(int argc, char *argv[])
 	};
 
 	if (envflag) {	/* clear env */
-		for (int i = 0; env_keep[i].name; i++) {
-			env_keep[i].value = strdup(getenv(env_keep[i].name));
-			if (!env_keep[i].value)
-				die("strdup:");
-		}
+		for (int i = 0; env_keep[i].name; i++)
+			env_keep[i].value = estrdup(getenv(env_keep[i].name));
 		environ = NULL; // in place of clearenv
 	}
 
@@ -285,9 +277,6 @@ static int authenticate(uid_t uid, char ask)
 	char *p = pw->pw_passwd;
 	int tty_fd = STDOUT_FILENO;
 
-	// but we have to be root
-	if (setuid(0) == -1)
-		die("setreuid:");
 	if (!strcmp(p, "x") || *p == '*' || *p == '!') {
 #if defined(__linux__)
 		// get exclusive access to shadow
@@ -300,8 +289,6 @@ static int authenticate(uid_t uid, char ask)
 		hash_p = sp->sp_pwdp;
 		endspent();
 		ulckpwdf();
-	//	if (setuid(uid) == -1)
-	//		die("setreuid:");
 #elif defined(__OpenBSD__)
 		// TODO: openbsd has getpwuid_passwd
 		struct passwd *op = getpwuid_shadow(uid);
@@ -469,3 +456,22 @@ void die(const char *fmt, ...)
 	exit(errno ? errno : EXIT_FAILURE);
 }
 
+void *emalloc(size_t s)
+{
+	if (!s || s == (size_t)-1)
+		die("bad malloc: invalid size");
+	void *p = malloc(s);
+	if (!p)
+		die("bad malloc:");
+	return p;
+}
+
+char *estrdup(const char *s)
+{
+	if (!s)
+		die("bad strdup: cannot duplicate NULL pointer");
+	char *r = strdup(s);
+	if (!r)
+		die("bad strdup:");
+	return r;
+}