Initial commit

.gitignore

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+bin/

Makefile

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+LIBRARIES = -Iinclude
+OUTPUT_DIR = ./bin
+OUTPUT_BIN = ${OUTPUT_DIR}/PROG
+OUTPUT = -o ${OUTPUT_BIN}
+SOURCES = ./src/* ./cmd/shell.c
+
+build: output_dir
+	gcc -Wall ${LIBRARIES} ${SOURCES} ${OUTPUT:PROG=rshell}
+
+debug: output_dir
+	gcc -Wall -g ${LIBRARIES} ${SOURCES} ${OUTPUT:PROG=rshell}
+
+output_dir:
+	mkdir -p ${OUTPUT_DIR}
+
+install: build
+	mv ${OUTPUT_BIN:PROG=rshell} /usr/sbin/rshell

README.md

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+# Reverse Shell Shell
+
+**IMPORTANT** this shell is **NOT** meant to be used for any serious applications.
+This is for academic purposes only!
+
+## Install
+
+```
+make build
+make install
+```

cmd/shell.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include "cmd_utils.h"
+
+#define clear() printf("\033[H\033[J")
+
+int main() {
+	int status_return = 0;
+	char *cmd;
+	char **args;
+
+	init_shell();
+
+	do {
+		cmd = read_input();
+		args = split_cmd(cmd);
+		status_return = reverse_execute(args);
+
+		free(cmd);
+		free(args);
+	} while(status_return != 255);
+	return EXIT_SUCCESS;
+}

include/cmd_utils.h

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+#include <stdio.h>
+#include <stdlib.h>
+
+int builtin_func_num();
+int show_author();
+void init_shell();
+int reverse_exit(char **args);
+int reverse_help(char **args);
+char *read_input();
+int reverse_external_execute(char **args);
+void reverse_command(char *args);
+int reverse_execute(char **args);
+char **split_cmd(char *line);
+

src/cmd_utils.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "cmd_utils.h"
+
+#define clear() printf("\033[H\033[J")
+
+static char *builtin_functions[] = {
+        "tixe",
+        "pleh",
+        "rohtua"
+};
+
+int (*builtin_func[]) (char **) = {
+        &reverse_exit,
+        &reverse_help,
+        &show_author
+};
+
+int builtin_func_num() {
+        return sizeof(builtin_functions) / sizeof(char *);
+}
+
+int show_author() {
+        static const char* author_message =
+                "Author: Spencer\n"
+                "Description: My first \"reverse shell\"\n"
+                "(╯°□°）╯︵ ┻━┻\n"
+                "";
+
+        printf("%s", author_message);
+
+        return 0;
+}
+
+void init_shell() {
+        static const char* init_message =
+                "======================================\n"
+                "= This Shell is *NOT* for Production =\n"
+                "=   For more information run help.   =\n"
+                "=   For information on the author:   =\n"
+                "=             run author.            =\n"
+                "======================================\n";
+
+        clear();
+        printf("%s", init_message);
+
+        return;
+}
+
+int reverse_exit(char **args) {
+        printf("Exiting...\n");
+        return 255;
+}
+
+int reverse_help(char **args) {
+        printf("ESREVER\n");
+        return 0;
+}
+
+char *read_input() {
+        int c, input_len = 0;
+        char *user_input = malloc((input_len+1) * sizeof(char));
+
+        printf(">> ");
+
+        while((c=getchar()) !='\n' && c != EOF) {
+                input_len++;
+                user_input = realloc(user_input, (input_len+1)*sizeof(char));
+                user_input[input_len-1] = (char)c;
+                user_input[input_len] = '\0';
+        }
+
+        if(input_len == 0) {
+                user_input=NULL;
+                return user_input;
+        }
+
+        return user_input;
+}
+
+int reverse_external_execute(char **args) {
+        pid_t pid;
+        int status;
+
+        pid = fork();
+        if (pid == 0) {
+                if(execvp(args[0], args) == -1) {
+                        printf("ERROR\n");
+                }
+                exit(EXIT_FAILURE);
+        } else if(pid < 0) {
+                printf("ERROR\n");
+        } else {
+                do {
+                        waitpid(pid, &status, WUNTRACED);
+                } while(!WIFEXITED(status) && !WIFSIGNALED(status));
+        }
+
+        return 1;
+}
+
+void reverse_command(char *args) {
+        char *temp_string;
+        temp_string = malloc(strlen(args));
+        strcpy(temp_string, args);
+        for(int i = 0; i < strlen(args); i++) {
+                temp_string[i] = args[strlen(args)-(i+1)];
+        }
+        strcpy(args, temp_string);
+        free(temp_string);
+        return;
+}
+
+int reverse_execute(char **args) {
+        if (args[0] == NULL) {
+                return 1;
+        }
+
+        for(int i = 0; i < builtin_func_num(); i++) {
+                if(strcmp(args[0], builtin_functions[i]) == 0) {
+                        return (*builtin_func[i])(args);
+                }
+        }
+        return reverse_external_execute(args);
+}
+
+char **split_cmd(char *line) {
+        size_t size = 8;
+        int pos = 0;
+        char **args = malloc(size * sizeof(char*));
+        char *arg = NULL;
+
+        if(line == NULL) {
+                *args=NULL;
+                return args;
+        }
+
+        reverse_command(line);
+
+        arg = strtok(line, " \t\r\n\a");
+        while (arg != NULL) {
+                args[pos] = arg;
+                pos++;
+
+                if (pos >= size) {
+                        size += 1;
+                        args = realloc(args, size * sizeof(char*));
+
+                }
+                arg = strtok(NULL, " \t\r\n\a");
+        }
+
+        args[pos] = NULL;
+        return args;
+}