initial commit

.gitignore

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+# Object files
+*.o
+*.ko
+*.obj
+*.elf
+
+# Precompiled Headers
+*.gch
+*.pch
+
+# Libraries
+*.lib
+*.a
+*.la
+*.lo
+
+# Shared objects (inc. Windows DLLs)
+*.dll
+*.so
+*.so.*
+*.dylib
+
+# Executables
+*.exe
+*.out
+*.app
+*.i*86
+*.x86_64
+*.hex
+c/client
+c/server
+
+# Debug files
+*.dSYM/
+
+# macOS shit
+.DS_Store
+
+# ide files
+.vscode
+

README.md

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+# zShell
+
+## Description
+
+Inspired by [inSecure-SHell](https://github.com/fffaraz/inSecure-SHell), this shell's goal is to be the tinyest and simplest remote shell.
+
+## Building
+
+```shell
+cd c
+make all
+```
+
+## Running
+
+To execute the server:
+
+```shell
+./server [-p port] [-s shell]
+```
+
+Connecting via:
+
+```shell
+./connect HOST
+```

c/Makefile

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+CC=gcc
+
+common: common.c
+	CC -c common.c -o common.o
+
+server: server.c common.o
+	CC server.c common.o -o server
+
+client: client.c common.o
+	CC client.c common.o -o client
+
+all: server client

c/client.c

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+#include <arpa/inet.h>
+#include <errno.h>
+#include <netdb.h>
+#include <netinet/in.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <termios.h>
+#include <unistd.h>
+
+#define DEFAULT_PORT "5910"
+#define BUFFERSIZE (64 * 1024)
+
+struct termios saved_attributes;
+void reset_input_mode()
+{
+    tcsetattr(STDIN_FILENO, TCSANOW, &saved_attributes);
+}
+
+void readline(int sockfd, char *buf)
+{
+    int pos = 0;
+    char c;
+    for (;;)
+    {
+        int n = recv(sockfd, &c, 1, 0);
+        if (n < 1)
+            break;
+        buf[pos++] = c;
+        if (c == '\n')
+            break;
+    }
+    buf[pos] = '\0';
+}
+
+void sigint_handler(int signum)
+{
+    printf("\n\nCaught signal: %d\n\n", signum);
+    exit(signum);
+}
+
+void print_addrinfo(struct addrinfo *input)
+{
+    int addr_i = 0;
+    for (struct addrinfo *p = input; p != NULL; p = p->ai_next)
+    {
+        char *ipver;
+        void *addr;
+
+        // get the pointer to the address itself, different fields in IPv4 and IPv6
+        if (p->ai_family == AF_INET)
+        {
+            ipver = "IPv4";
+            struct sockaddr_in *ipv4 = (struct sockaddr_in *)p->ai_addr;
+            addr = &(ipv4->sin_addr);
+        }
+        else
+        {
+            ipver = "IPv6";
+            struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)p->ai_addr;
+            addr = &(ipv6->sin6_addr);
+        }
+
+        char ipstr[INET6_ADDRSTRLEN];
+        inet_ntop(p->ai_family, addr, ipstr, sizeof(ipstr)); // convert the IP to a string
+        printf("%2d. %s: %s\n", ++addr_i, ipver, ipstr);
+    }
+}
+
+int main(int argc, char **argv)
+{
+    if (argc != 2)
+    {
+        fprintf(stderr, "usage: %s hostname\n", argv[0]);
+        return 1;
+    }
+
+    signal(SIGINT, sigint_handler);
+
+    printf("Looking up addresses for %s ...\n", argv[1]);
+
+    struct addrinfo hints;
+    memset(&hints, 0, sizeof(hints));
+    hints.ai_family = AF_UNSPEC; // AF_INET or AF_INET6 to force version
+    hints.ai_socktype = SOCK_STREAM;
+
+    struct addrinfo *dnsres;
+    int status = getaddrinfo(argv[1], DEFAULT_PORT, &hints, &dnsres);
+    if (status != 0)
+    {
+        fprintf(stderr, "dns lookup failed: %s\n", gai_strerror(status));
+        return 2;
+    }
+
+    print_addrinfo(dnsres);
+
+    printf("Connecting to %s ...\n", "the server");
+    int sockfd = socket(dnsres->ai_family, dnsres->ai_socktype, dnsres->ai_protocol);
+
+    if (connect(sockfd, dnsres->ai_addr, dnsres->ai_addrlen) != 0)
+    {
+        perror("connect");
+        return 3;
+    }
+    printf("Connected.\n");
+
+    freeaddrinfo(dnsres); // frees the memory that was dynamically allocated for the linked lists by getaddrinfo
+
+    char buf[BUFFERSIZE + 1];
+    int nbytes, mbytes;
+
+    // Make sure stdin is a terminal.
+    if (!isatty(STDIN_FILENO))
+    {
+        fprintf(stderr, "Not a terminal.\n");
+        exit(EXIT_FAILURE);
+    }
+
+    // Save the terminal attributes so we can restore them later.
+    tcgetattr(STDIN_FILENO, &saved_attributes);
+    atexit(reset_input_mode);
+
+    // Set the funny terminal modes.
+    struct termios tattr;
+    tcgetattr(STDIN_FILENO, &tattr);
+    tattr.c_lflag &= ~(ICANON | ECHO); // Clear ICANON and ECHO.
+    tattr.c_cc[VMIN] = 1;
+    tattr.c_cc[VTIME] = 0;
+    tcsetattr(STDIN_FILENO, TCSAFLUSH, &tattr);
+
+    fd_set master, readfds;
+    FD_ZERO(&master);
+    FD_SET(STDIN_FILENO, &master);
+    FD_SET(sockfd, &master);
+
+    for (;;)
+    {
+        readfds = master;
+
+        if (select(sockfd + 1, &readfds, NULL, NULL, NULL) == -1)
+        {
+            perror("select");
+            return 7;
+        }
+
+        if (FD_ISSET(STDIN_FILENO, &readfds))
+        {
+            nbytes = read(STDIN_FILENO, buf, BUFFERSIZE);
+            if (nbytes < 1)
+            {
+                // perror("stdin closed");
+                break;
+            }
+            mbytes = send(sockfd, buf, nbytes, 0);
+        }
+
+        if (FD_ISSET(sockfd, &readfds))
+        {
+            nbytes = recv(sockfd, buf, BUFFERSIZE, 0);
+            if (nbytes < 1)
+            {
+                // perror("sockfd closed");
+                break;
+            }
+            mbytes = write(STDOUT_FILENO, buf, nbytes);
+        }
+        if (nbytes != mbytes)
+            printf("nbytes [%d] != mbytes [%d] \n", nbytes, mbytes);
+    }
+
+    close(sockfd);
+    printf("Bye 👋");
+    return 0;
+}

c/common.c

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+#include <stdarg.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdbool.h>
+#include <sys/socket.h>
+
+#include "common.h"
+
+void trace(const char *prefix, const char *fmt, ...)
+{
+    char line[1024];
+    char prefixed_line[1024];
+
+    va_list args;
+    va_start(args, fmt);
+    vsprintf(line, fmt, args);
+    va_end(args);
+
+    sprintf(prefixed_line, "%s: %s", prefix, line);
+    puts(prefixed_line);
+}
+
+bool sendall(int sockfd, const char *buf, size_t len)
+{
+    size_t total_bytes = 0;
+    size_t bytes = 0;
+
+    while (len > 0) {
+        bytes = send(sockfd, buf + total_bytes, len, 0);
+        CHECK(bytes != -1);
+
+        total_bytes += bytes;
+        len -= bytes;
+    }
+
+    return true;
+
+error:
+    TRACE("error");
+    return false;
+}

c/common.h

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+#ifndef __COMMON_H_
+#define __COMMON_H_
+
+#include <stdarg.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+#define TRACE(...) trace(__PRETTY_FUNCTION__, __VA_ARGS__)
+#define CHECK(expression) if (!(expression)) { goto error; }
+
+void trace(const char *prefix, const char *fmt, ...);
+
+bool sendall(int sockfd, const char *buf, size_t len);
+
+
+
+#endif // __COMMON_H_