Initial commit

.gitignore

@@ -0,0 +1 @@
+/usuid

make

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+#!/usr/bin/env bash
+set -e
+gcc src/main.c -o "usuid" -Os -Werror -Wall
+sudo chown root "usuid.usuid"
+sudo chmod 755 "usuid.usuid"
+sudo chown root "usuid"
+sudo chmod 755 "usuid"
+sudo chmod u+s "usuid"

src/main.c

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+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <stdio.h>
+#include <linux/limits.h>
+#include <errno.h>
+
+void *emalloc(void *ptr, size_t size) {
+	void *m = realloc(ptr,size);
+	if (m == NULL) {
+		fprintf(stderr,"[usuid] error 255: malloc failed\n");
+		exit(255);
+	}
+	return m;
+}
+
+int main(int argc, char **argv) {
+	extern char **environ;
+	environ = NULL; // Clear environment to boost security
+	int uid = getuid(); // User who's calling the program
+	int euid = geteuid(); // User who owns the program
+	
+	// Strip first argument, and move them by 1
+	char **cmd;
+	if (argc > 1) {
+		cmd = emalloc(NULL,(argc + 1) * sizeof(char*));
+		int i = 1;
+		while (i < argc) {
+			cmd[i] = argv[i];
+			++i;
+		}
+	} else {
+		cmd = emalloc(NULL,sizeof(char*) * 2);
+	}
+	cmd[argc] = NULL;
+	
+	// Get current program name
+	cmd[0] = emalloc(NULL,PATH_MAX);
+	setuid(euid);
+	ssize_t length = readlink("/proc/self/exe",cmd[0],PATH_MAX);
+	setuid(uid);
+	if (length == -1) {
+		fprintf(stderr,"[usuid] error 254: Could not get own program name (/proc/self/exe)\n");
+		return 254;
+	}
+	
+	// Get new program name
+	strcat(cmd[0],".usuid");
+	cmd[0] = emalloc(cmd[0],length + (sizeof(char) * 7)); // Why do I have to put 7 for it to work? 6 should be sufficient? Null terminator? Lé C memory corruption? Yummy?
+	
+	// Run program
+	setuid(euid);
+	if (execv(cmd[0],cmd) == -1) {
+		// Handle errors
+		setuid(uid);
+		fprintf(stderr,"[usuid] error %d: %s\n",253 - errno,strerror(errno));
+		return 253 - errno;
+	}
+}

usuid.usuid

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+#!/usr/bin/env lua5.3
+print("i am root\n\narguments:")
+for i,a in ipairs(arg) do
+	print("* " ..a)
+end