commit 440f4151a20aeb9817f9cc726b6582d6fc998059
Author: E. S. <the@rootless.one>
Date:   Wed Nov 27 02:19:12 2024 +0300

    initial

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..aeaa3ad
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+*.o
+rl_clearnet
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..26ab702
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,22 @@
+CC	:= gcc
+
+CFLAGS	= -O2 -std=c99 -Wall -W
+LDFLAGS	=
+
+INSTALL	= /usr/bin/env install
+PREFIX	= /usr/local
+
+all: rl_clearnet.o
+	$(CC) $(CFLAGS) -o rl_clearnet $^ $(LDFLAGS)
+
+install: all
+	$(INSTALL) rl_clearnet $(PREFIX)/bin
+	chmod u+s $(PREFIX)/bin/rl_clearnet
+
+clean:
+	rm -f *.o rl_clearnet
+
+%.o: %.c
+	$(CC) $(CFLAGS) -c $^ -I. -o $@
+
+.PHONY: all install clean
diff --git a/config.def.h b/config.def.h
new file mode 100644
index 0000000..9500c6e
--- /dev/null
+++ b/config.def.h
@@ -0,0 +1,13 @@
+#define NETNS_PATH "/run/netns/clearnet"
+#define DHCPCD_PATH "/usr/bin/dhcpcd"
+#define EXEC_UID 1000
+#define EXEC_GUD 1000
+
+static char *env_vars[] = {"DISPLAY", "HOME", "PWD", "EDITOR", "USER", "XAUTHORITY", "LANG", "DBUS_SESSION_BUS_ADDRESS"};
+
+static char *firefox_cmd[] = {"firefox", "-P", "clearnet", NULL};
+static char *thunderbird_cmd[] = {"thunderbird", "-P", "clearnet", NULL};
+static char *ping_cmd[] = {"ping", "8.8.8.8", NULL};
+
+static char **commands[] = {firefox_cmd, thunderbird_cmd, ping_cmd};
+static char *aliases[] = {"fx", "tb", "ping"};
diff --git a/rl_clearnet.c b/rl_clearnet.c
new file mode 100644
index 0000000..080e65e
--- /dev/null
+++ b/rl_clearnet.c
@@ -0,0 +1,350 @@
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sched.h>
+#include <fcntl.h>
+#include <assert.h>
+#include <signal.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <linux/limits.h>
+#include <linux/if_arp.h>
+
+#include "rl_clearnet.h"
+#include "config.def.h"
+
+static pid_t child_pid = -1;
+
+static void sigint_handler(int);
+static void usage(const char *);
+static int get_default_iface(char [IFNAMSIZ]);
+static int get_domain_name_servers(const char *, char *[4]);
+
+int
+main(int argc, char* argv[])
+{
+    assert(ARRAY_SIZE(commands) == ARRAY_SIZE(aliases));
+
+    int rc = 1;
+    int tempfd = 0;
+    int nsfd = 0;
+    char cwd[PATH_MAX];
+    char temp_name[PATH_MAX] = {0};
+    char iface[IFNAMSIZ];
+    int mounted = 0;
+    int cmdi = -1;
+    char *dns[4] = {0};
+    size_t i;
+
+    if (argc != 2) {
+        usage(argv[0]);
+        return 1;
+    }
+
+    if (!strcmp(argv[1], "-h")) {
+        usage(argv[0]);
+        return 1;
+    }
+
+    for (i = 0; i < (int)ARRAY_SIZE(aliases); i++) {
+        if (!strcmp(argv[1], aliases[i])) {
+            cmdi = (int)i;
+            break;
+        }
+    }
+
+    if (cmdi == -1) {
+        fprintf(stderr, "error: alias %s not found\n", argv[1]);
+        return 1;
+    }
+
+    if (geteuid() != 0) {
+        fprintf(stderr, "error: you must be root.\n");
+        return 1;
+    }
+
+    if (unshare(CLONE_NEWNS) == -1) {
+        perror("unshare");
+        return 1;
+    }
+
+    /* save cwd */
+    if (!getcwd(cwd, PATH_MAX)) {
+        perror("getcwd");
+        return 1;
+    }
+
+    /* get default network interface */
+    if (get_default_iface(iface) != 0) {
+        fprintf(stderr, "error: get_default_iface failed");
+        return 1;
+    }
+
+    /* get default domain name servers */
+    if (get_domain_name_servers(iface, dns) != 0) {
+        fprintf(stderr, "error: get_domain_name_servers failed");
+        return 1;
+    }
+
+    /* create temp resolv.conf */
+    strcpy(temp_name, "/tmp/rl_clearnet.XXXXXX");
+    if ((tempfd = mkstemp(temp_name)) == -1) {
+        perror("mkstemp");
+        goto end;
+    }
+    for (i = 0; i < ARRAY_SIZE(dns); i++) {
+        if (dns[i])
+            dprintf(tempfd, "nameserver %s\n", dns[i]);
+    }
+    close(tempfd);
+    chmod(temp_name, 0644);
+
+    /* bind-mount it as /etc/resolv.conf */
+    if (mount(temp_name, "/etc/resolv.conf", NULL, MS_BIND, NULL) == -1) {
+        perror("mount");
+        goto end;
+    }
+    mounted = 1;
+
+    nsfd = open(NETNS_PATH, O_RDONLY);
+    if (nsfd == -1) {
+        perror("open");
+        goto end;
+    }
+
+    /* change to netns */
+    if (setns(nsfd, CLONE_NEWNET) == -1) {
+        perror("setns");
+        goto end;
+    }
+
+    /* handle ctrl+c */
+    struct sigaction sa;
+    sa.sa_handler = sigint_handler;
+    sigemptyset(&sa.sa_mask);
+    sa.sa_flags = 0;
+    sigaction(SIGINT, &sa, NULL);
+
+    child_pid = fork();
+    if (!child_pid) {
+        /* change real and effective user and group */
+        if (EXEC_GUD != getegid()) {
+            if (setregid(EXEC_GUD, EXEC_GUD) == -1) {
+                perror("setregid");
+                goto end;
+            }
+        }
+
+        if (EXEC_UID != geteuid()) {
+            if (setreuid(EXEC_UID, EXEC_UID) == -1) {
+                perror("setreuid");
+                goto end;
+            }
+        }
+
+        /* restore cwd */
+        if (chdir(cwd) == -1) {
+            perror("chdir");
+            goto end;
+        }
+
+        /* allocate environment variables list */
+        char **envp = malloc((ARRAY_SIZE(env_vars) + 1) * sizeof(char *));
+        if (!envp) {
+            perror("malloc");
+            goto end;
+        }
+
+        size_t count = 0;
+        for (i = 0; i < ARRAY_SIZE(env_vars); i++) {
+            char *value = getenv(env_vars[i]);
+            if (value && *value) {
+                size_t len = strlen(env_vars[i]) + strlen(value) + 2; // key=value + '=' + '\0'
+                envp[count] = malloc(len);
+                if (!envp[count]) {
+                    for (size_t j = 0; j < count; j++)
+                        free(envp[j]);
+                    free(envp);
+                    perror("malloc");
+                    return 1;
+                }
+                snprintf(envp[count], len, "%s=%s", env_vars[i], value);
+                count++;
+            }
+        }
+        envp[count] = NULL;
+
+        /* launch program */
+        if (execvpe(*commands[cmdi], (char *const *)commands[cmdi], envp) == -1)
+            perror("execvpe");
+        else
+            rc = 0;
+        for (i = 0; i < count; i++)
+            free(envp[i]);
+        free(envp);
+        return rc;
+    }
+
+    rc = 0;
+
+    int status = 0;
+    wait(&status);
+    if (WIFEXITED(status))
+        rc = WEXITSTATUS(status);
+    else if (WIFSIGNALED(status))
+        rc = 128 + WTERMSIG(status);
+
+end:
+    for (i = 0; i < ARRAY_SIZE(dns); i++) {
+        if (dns[i])
+            free(dns[i]);
+    }
+
+    if (mounted)
+        umount(temp_name);
+
+    if (nsfd > 0)
+        close(nsfd);
+
+    if (*temp_name)
+        unlink(temp_name);
+
+    return rc;
+}
+
+void
+usage(const char *prog)
+{
+    printf("Usage: %s [-h] ALIAS\n\n", prog);
+    printf("Aliases:\n");
+    for (size_t i = 0; i < ARRAY_SIZE(aliases); i++)
+        printf("    %s\n", aliases[i]);
+    printf("\n");
+}
+
+int
+get_default_iface(char dst[IFNAMSIZ])
+{
+    FILE *fp;
+    char line[256];
+    char iface[IFNAMSIZ];
+    char destination[64], gateway[64], flags[64], refcnt[64], use[64], metric[64], mask[64], mtu[64], window[64], irtt[64];
+    struct ifreq ifr;
+    int found = 0;
+
+    fp = fopen("/proc/net/route", "r");
+    if (!fp) {
+        perror("fopen");
+        return 1;
+    }
+
+    fgets(line, sizeof(line), fp); /* skip header */
+    while (fgets(line, sizeof(line), fp)) {
+        sscanf(line, "%s %s %s %s %s %s %s %s %s %s %s",
+               iface, destination, gateway, flags, refcnt, use, metric, mask, mtu, window, irtt);
+
+        /* check if default route */
+        if (strcmp(destination, "00000000") == 0) {
+            int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
+            if (sockfd < 0) {
+                perror("socket");
+                fclose(fp);
+                return 1;
+            }
+
+            memset(&ifr, 0, sizeof(ifr));
+            strlcpy(ifr.ifr_name, iface, IFNAMSIZ-1);
+
+            if (ioctl(sockfd, SIOCGIFHWADDR, &ifr) == 0) {
+                if (ifr.ifr_hwaddr.sa_family == ARPHRD_ETHER) {
+                    strlcpy(dst, iface, IFNAMSIZ-1);
+                    found = 1;
+                    close(sockfd);
+                    break;
+                }
+            } else {
+                perror("ioctl");
+            }
+            close(sockfd);
+        }
+    }
+
+    fclose(fp);
+
+    return found ? 0 : 1;
+}
+
+int
+get_domain_name_servers(const char *iface, char *servers[4])
+{
+    char cmd[256];
+    FILE *fp;
+    char line[1024];
+    char domain_name_servers_line[1024];
+    int found = 0;
+    int server_count = 0;
+    size_t len;
+
+    if (snprintf(cmd, sizeof(cmd), DHCPCD_PATH " -U %s", iface) >= (int)sizeof(cmd)) {
+        fprintf(stderr, "error: interface name is too long\n");
+        return 1;
+    }
+
+    fp = popen(cmd, "r");
+    if (!fp) {
+        perror("popen");
+        return 1;
+    }
+
+    while (fgets(line, sizeof(line), fp)) {
+        /* remove any trailing newline character */
+        line[strcspn(line, "\n")] = '\0';
+
+        /* if line starts with "domain_name_servers=" */
+        if (strncmp(line, "domain_name_servers=", 20) == 0) {
+            found = 1;
+            len = strlen(line + 20);
+            if (len >= sizeof(domain_name_servers_line))
+                len = sizeof(domain_name_servers_line)-1;
+            memcpy(domain_name_servers_line, line + 20, len);
+            domain_name_servers_line[len] = '\0';
+            break;
+        }
+    }
+
+    if (pclose(fp) == -1) {
+        perror("pclose");
+        return 1;
+    }
+
+    if (!found) {
+        fprintf(stderr, "error: domain_name_servers not found\n");
+        return 1;
+    }
+
+    /* parse domain_name_servers_line */
+    char *token = strtok(domain_name_servers_line, " ");
+    while (token && server_count < 4) {
+        servers[server_count] = strdup(token);
+        if (!servers[server_count]) {
+            fprintf(stderr, "error: memory allocation failed\n");
+            return 1;
+        }
+        server_count++;
+        token = strtok(NULL, " ");
+    }
+
+    return 0;
+}
+
+void
+sigint_handler(int sig)
+{
+    (void)sig;
+    if (!child_pid)
+        kill(child_pid, SIGTERM);
+}
\ No newline at end of file
diff --git a/rl_clearnet.h b/rl_clearnet.h
new file mode 100644
index 0000000..ca31914
--- /dev/null
+++ b/rl_clearnet.h
@@ -0,0 +1 @@
+#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))