initial commit

ns_child_exec.c

@@ -0,0 +1,97 @@
+/* ns_child_exec.c
+
+   Copyright 2013, Michael Kerrisk
+   Licensed under GNU General Public License v2 or later
+
+   Create a child process that executes a shell command in new namespace(s).
+*/
+#define _GNU_SOURCE
+#include <sched.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <sys/wait.h>
+#include <signal.h>
+#include <stdio.h>
+
+/* A simple error-handling function: print an error message based
+   on the value in 'errno' and terminate the calling process */
+
+#define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
+                        } while (0)
+
+static void
+usage(char *pname)
+{
+    fprintf(stderr, "Usage: %s [options] cmd [arg...]\n", pname);
+    fprintf(stderr, "Options can be:\n");
+    fprintf(stderr, "    -i   new IPC namespace\n");
+    fprintf(stderr, "    -m   new mount namespace\n");
+    fprintf(stderr, "    -n   new network namespace\n");
+    fprintf(stderr, "    -p   new PID namespace\n");
+    fprintf(stderr, "    -u   new UTS namespace\n");
+    fprintf(stderr, "    -U   new user namespace\n");
+    fprintf(stderr, "    -v   Display verbose messages\n");
+    exit(EXIT_FAILURE);
+}
+
+static int              /* Start function for cloned child */
+childFunc(void *arg)
+{
+    char **argv = arg;
+
+    execvp(argv[0], &argv[0]);
+    errExit("execvp");
+}
+
+#define STACK_SIZE (1024 * 1024)
+
+static char child_stack[STACK_SIZE];    /* Space for child's stack */
+
+int
+main(int argc, char *argv[])
+{
+    int flags, opt, verbose;
+    pid_t child_pid;
+
+    flags = 0;
+    verbose = 0;
+
+    /* Parse command-line options. The initial '+' character in
+       the final getopt() argument prevents GNU-style permutation
+       of command-line options. That's useful, since sometimes
+       the 'command' to be executed by this program itself
+       has command-line options. We don't want getopt() to treat
+       those as options to this program. */
+
+    while ((opt = getopt(argc, argv, "+imnpuUv")) != -1) {
+        switch (opt) {
+        case 'i': flags |= CLONE_NEWIPC;        break;
+        case 'm': flags |= CLONE_NEWNS;         break;
+        case 'n': flags |= CLONE_NEWNET;        break;
+        case 'p': flags |= CLONE_NEWPID;        break;
+        case 'u': flags |= CLONE_NEWUTS;        break;
+        case 'U': flags |= CLONE_NEWUSER;       break;
+        case 'v': verbose = 1;                  break;
+        default:  usage(argv[0]);
+        }
+    }
+
+    child_pid = clone(childFunc,
+                    child_stack + STACK_SIZE,
+                    flags | SIGCHLD, &argv[optind]);
+    if (child_pid == -1)
+        errExit("clone");
+
+    if (verbose)
+        printf("%s: PID of child created by clone() is %ld\n",
+                argv[0], (long) child_pid);
+
+    /* Parent falls through to here */
+
+    if (waitpid(child_pid, NULL, 0) == -1)      /* Wait for child */
+        errExit("waitpid");
+
+    if (verbose)
+        printf("%s: terminating\n", argv[0]);
+    exit(EXIT_SUCCESS);
+}