1 files changed, 124 insertions, 0 deletions
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..7cb565b
--- /dev/null
+++ b/main.c
@@ -0,0 +1,124 @@
+/* See LICENSE file for copyright and license details. */
+#define _GNU_SOURCE
+#include <sched.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/wait.h>
+#include "mount.c"
+
+#ifndef MNTRUN_VERSION
+#define MNTRUN_VERSION "(unknown)"
+#endif
+
+#define USAGE "usage: mntrun [-dhv] [-b source dest] [[-o|-m] upperdir lowerdir workdir mountpoint] command\n"
+
+static inline int checkflag(char *arg, char f) {
+    return arg && (arg[0] == '-' && arg[1] == f && arg[2] == '\0');
+}
+
+int namespace_main(void *data) {
+    uid_t uid = getuid();
+    gid_t gid = getgid();
+
+    int verbose = 0;
+    char **argv = data;
+
+    if(checkflag(argv[0], 'h')) {
+        fputs(USAGE, stderr);
+        return EXIT_SUCCESS;
+    }
+
+    if(checkflag(argv[0], 'v')) {
+        puts("mntrun " MNTRUN_VERSION);
+        return EXIT_SUCCESS;
+    }
+
+    if(checkflag(argv[0], 'd')) {
+        verbose = 1;
+        argv ++;
+    }
+
+    /* Jump back here over-and-over until all mount directives are parsed. */
+    do_mounts:
+    if(checkflag(argv[0], 'b')) {
+        if(!argv[1] || !argv[2]) goto exit_usage;
+
+        if(mount_bind(argv[1], argv[2]) == -1) {
+            if(errno) fprintf(stderr, "Failed to bind '%s' to '%s': %s\n", argv[1], argv[2], strerror(errno));
+            return EXIT_FAILURE;
+        }
+        argv += 3;
+        goto do_mounts;
+    }
+
+    int merge = 0;
+    if(checkflag(argv[0], 'o') || (merge = checkflag(argv[0], 'm'))) {
+        char *type_str = merge ? "merge" : "overlay";
+
+        if(!argv[1] || !argv[2] || !argv[3] || !argv[4]) goto exit_usage;
+        if(verbose) printf("[%s]\n\tlower=%s\n\tupper=%s\n\twork=%s\n\tmount=%s\n", type_str, argv[1], argv[2], argv[3], argv[4]);
+
+        char *lowers = argv[1];
+        if(merge) {
+            lowers = malloc(strlen(argv[4]) + 1 + strlen(argv[1]));
+            sprintf(lowers, "%s:%s", argv[4], argv[1]);
+        }
+
+        if(mount_overlay(uid, gid, lowers, argv[2], argv[3], argv[4]) == -1) {
+            if(errno) fprintf(stderr, "Failed to mount %s on '%s': %s\n", type_str, argv[4], strerror(errno));
+            return EXIT_FAILURE;
+        }
+        argv += 5;
+        if(merge) {
+            free(lowers);
+            merge = 0;
+        }
+        goto do_mounts;
+    }
+    /* Check if a command was specified */
+    if(!argv[0]) goto exit_usage;
+
+    setuid(uid);
+
+    /* These next lines take the remaining values in `argv` and join them with spaces in `command`. */
+    int charc;
+    for(int i = 0; argv[i]; i ++) charc += strlen(argv[i]);
+    char *command = malloc(charc + 1);
+    command[0] = '\0';
+    for(int i = 0; argv[i]; i ++) {
+        strcat(command, " ");
+        strcat(command, argv[i]);
+    }
+    
+    int status = system(command);
+    if(status == -1) {
+        perror("system");
+        return EXIT_FAILURE;
+    }
+    return status;
+
+exit_usage:
+    fputs(USAGE, stderr);
+    return EXIT_FAILURE;
+}
+
+int main(int argc, char **argv) {
+    #define STACK_SIZE 1024 * 1024
+    char *stack = malloc(STACK_SIZE);
+    pid_t pid = clone(namespace_main, stack + STACK_SIZE, CLONE_NEWNS | SIGCHLD, argv + 1);
+    if(pid == -1) {
+        perror("Failed to create a new mount namespace");
+        return EXIT_FAILURE;
+    }
+    
+    int wstatus;
+    if (waitpid(pid, &wstatus, 0) == -1) {
+        /* The only error which may occurs is EINTR, but I'm not 100% sure. */
+        perror("waitpid");
+        return EXIT_FAILURE;
+    }
+    return WEXITSTATUS(wstatus);
+}