--- /dev/null
+/* vi: set sw=4 ts=4: */
+/*
+ * Mini nsenter implementation for busybox.
+ *
+ * Copyright (C) 2016 by Bartosz Golaszewski <bartekgola@gmail.com>
+ *
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
+ */
+
+//config:config NSENTER
+//config: bool "nsenter"
+//config: default y
+//config: select PLATFORM_LINUX
+//config: help
+//config: Run program with namespaces of other processes.
+//config:
+//config:config FEATURE_NSENTER_LONG_OPTS
+//config: bool "Enable long options"
+//config: default y
+//config: depends on NSENTER && LONG_OPTS
+//config: help
+//config: Support long options for the nsenter applet. This makes
+//config: the busybox implementation more compatible with upstream.
+
+//applet:IF_NSENTER(APPLET(nsenter, BB_DIR_USR_BIN, BB_SUID_DROP))
+
+//kbuild:lib-$(CONFIG_NSENTER) += nsenter.o
+
+//usage:#define nsenter_trivial_usage
+//usage: "[OPTIONS] [PROG [ARGS]]"
+//usage:#if ENABLE_FEATURE_NSENTER_LONG_OPTS
+//usage:#define nsenter_full_usage "\n"
+//usage: "\n -t, --target=PID Target process to get namespaces from"
+//usage: "\n -m, --mount[=FILE] Enter mount namespace"
+//usage: "\n -u, --uts[=FILE] Enter UTS namespace (hostname etc)"
+//usage: "\n -i, --ipc[=FILE] Enter System V IPC namespace"
+//usage: "\n -n, --net[=FILE] Enter network namespace"
+//usage: "\n -p, --pid[=FILE] Enter pid namespace"
+//usage: "\n -U, --user[=FILE] Enter user namespace"
+//usage: "\n -S, --setuid=UID Set uid in entered namespace"
+//usage: "\n -G, --setgid=GID Set gid in entered namespace"
+//usage: "\n --preserve-credentials Don't touch uids or gids"
+//usage: "\n -r, --root[=DIR] Set root directory"
+//usage: "\n -w, --wd[=DIR] Set working directory"
+//usage: "\n -F, --no-fork Don't fork before exec'ing PROG"
+//usage:#else
+//usage:#define nsenter_full_usage "\n"
+//usage: "\n -t PID Target process to get namespaces from"
+//usage: "\n -m[FILE] Enter mount namespace"
+//usage: "\n -u[FILE] Enter UTS namespace (hostname etc)"
+//usage: "\n -i[FILE] Enter System V IPC namespace"
+//usage: "\n -n[FILE] Enter network namespace"
+//usage: "\n -p[FILE] Enter pid namespace"
+//usage: "\n -U[FILE] Enter user namespace"
+//usage: "\n -S UID Set uid in entered namespace"
+//usage: "\n -G GID Set gid in entered namespace"
+//usage: "\n -r[DIR] Set root directory"
+//usage: "\n -w[DIR] Set working directory"
+//usage: "\n -F Don't fork before exec'ing PROG"
+//usage:#endif
+
+#include <sched.h>
+#include "libbb.h"
+
+struct namespace_descr {
+ int flag; /* value passed to setns() */
+ char ns_nsfile8[8]; /* "ns/" + namespace file in process' procfs entry */
+};
+
+struct namespace_ctx {
+ char *path; /* optional path to a custom ns file */
+ int fd; /* opened namespace file descriptor */
+};
+
+enum {
+ OPT_user = 1 << 0,
+ OPT_ipc = 1 << 1,
+ OPT_uts = 1 << 2,
+ OPT_network = 1 << 3,
+ OPT_pid = 1 << 4,
+ OPT_mount = 1 << 5,
+ OPT_target = 1 << 6,
+ OPT_setuid = 1 << 7,
+ OPT_setgid = 1 << 8,
+ OPT_root = 1 << 9,
+ OPT_wd = 1 << 10,
+ OPT_nofork = 1 << 11,
+ OPT_prescred = (1 << 12) * ENABLE_FEATURE_NSENTER_LONG_OPTS,
+};
+enum {
+ NS_USR_POS = 0,
+ NS_IPC_POS,
+ NS_UTS_POS,
+ NS_NET_POS,
+ NS_PID_POS,
+ NS_MNT_POS,
+ NS_COUNT,
+};
+/*
+ * The order is significant in nsenter.
+ * The user namespace comes first, so that it is entered first.
+ * This gives an unprivileged user the potential to enter other namespaces.
+ */
+static const struct namespace_descr ns_list[] = {
+ { CLONE_NEWUSER, "ns/user", },
+ { CLONE_NEWIPC, "ns/ipc", },
+ { CLONE_NEWUTS, "ns/uts", },
+ { CLONE_NEWNET, "ns/net", },
+ { CLONE_NEWPID, "ns/pid", },
+ { CLONE_NEWNS, "ns/mnt", },
+};
+/*
+ * Upstream nsenter doesn't support the short option for --preserve-credentials
+ */
+static const char opt_str[] = "U::i::u::n::p::m::""t+S+G+r::w::F";
+
+#if ENABLE_FEATURE_NSENTER_LONG_OPTS
+static const char nsenter_longopts[] ALIGN1 =
+ "user\0" Optional_argument "U"
+ "ipc\0" Optional_argument "i"
+ "uts\0" Optional_argument "u"
+ "network\0" Optional_argument "n"
+ "pid\0" Optional_argument "p"
+ "mount\0" Optional_argument "m"
+ "target\0" Required_argument "t"
+ "setuid\0" Required_argument "S"
+ "setgid\0" Required_argument "G"
+ "root\0" Optional_argument "r"
+ "wd\0" Optional_argument "w"
+ "no-fork\0" No_argument "F"
+ "preserve-credentials\0" No_argument "\xff"
+ ;
+#endif
+
+/*
+ * Open a file and return the new descriptor. If a full path is provided in
+ * fs_path, then the file to which it points is opened. Otherwise (fd_path is
+ * NULL) the routine builds a path to a procfs file using the following
+ * template: '/proc/<target_pid>/<target_file>'.
+ */
+static int open_by_path_or_target(const char *path,
+ pid_t target_pid, const char *target_file)
+{
+ char proc_path_buf[sizeof("/proc/%u/1234567890") + sizeof(int)*3];
+
+ if (!path) {
+ if (target_pid == 0) {
+ /* Example:
+ * "nsenter -p PROG" - neither -pFILE nor -tPID given.
+ */
+ bb_show_usage();
+ }
+ snprintf(proc_path_buf, sizeof(proc_path_buf),
+ "/proc/%u/%s", (unsigned)target_pid, target_file);
+ path = proc_path_buf;
+ }
+
+ return xopen(path, O_RDONLY);
+}
+
+int nsenter_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int nsenter_main(int argc UNUSED_PARAM, char **argv)
+{
+ int i;
+ unsigned int opts;
+ const char *root_dir_str = NULL;
+ const char *wd_str = NULL;
+ struct namespace_ctx ns_ctx_list[NS_COUNT];
+ int setgroups_failed;
+ int root_fd, wd_fd;
+ int target_pid = 0;
+ int uid = 0;
+ int gid = 0;
+
+ memset(ns_ctx_list, 0, sizeof(ns_ctx_list));
+
+ IF_FEATURE_NSENTER_LONG_OPTS(applet_long_options = nsenter_longopts);
+ opts = getopt32(argv, opt_str,
+ &ns_ctx_list[NS_USR_POS].path,
+ &ns_ctx_list[NS_IPC_POS].path,
+ &ns_ctx_list[NS_UTS_POS].path,
+ &ns_ctx_list[NS_NET_POS].path,
+ &ns_ctx_list[NS_PID_POS].path,
+ &ns_ctx_list[NS_MNT_POS].path,
+ &target_pid, &uid, &gid,
+ &root_dir_str, &wd_str
+ );
+ argv += optind;
+
+ root_fd = wd_fd = -1;
+ if (opts & OPT_root)
+ root_fd = open_by_path_or_target(root_dir_str,
+ target_pid, "root");
+ if (opts & OPT_wd)
+ wd_fd = open_by_path_or_target(wd_str, target_pid, "cwd");
+
+ for (i = 0; i < NS_COUNT; i++) {
+ const struct namespace_descr *ns = &ns_list[i];
+ struct namespace_ctx *ns_ctx = &ns_ctx_list[i];
+
+ ns_ctx->fd = -1;
+ if (opts & (1 << i))
+ ns_ctx->fd = open_by_path_or_target(ns_ctx->path,
+ target_pid, ns->ns_nsfile8);
+ }
+
+ /*
+ * Entering the user namespace without --preserve-credentials implies
+ * --setuid & --setgid and clearing root's groups.
+ */
+ setgroups_failed = 0;
+ if ((opts & OPT_user) && !(opts & OPT_prescred)) {
+ opts |= (OPT_setuid | OPT_setgid);
+ /*
+ * We call setgroups() before and after setns() and only
+ * bail-out if it fails twice.
+ */
+ setgroups_failed = (setgroups(0, NULL) < 0);
+ }
+
+ for (i = 0; i < NS_COUNT; i++) {
+ const struct namespace_descr *ns = &ns_list[i];
+ struct namespace_ctx *ns_ctx = &ns_ctx_list[i];
+
+ if (ns_ctx->fd < 0)
+ continue;
+ if (setns(ns_ctx->fd, ns->flag)) {
+ bb_perror_msg_and_die(
+ "setns(): can't reassociate to namespace '%s'",
+ ns->ns_nsfile8 + 3 /* skip over "ns/" */
+ );
+ }
+ /*close(ns_ctx->fd);*/
+ /*ns_ctx->fd = -1;*/
+ }
+
+ if (root_fd >= 0) {
+ if (wd_fd < 0) {
+ /*
+ * Save the current working directory if we're not
+ * changing it.
+ */
+ wd_fd = xopen(".", O_RDONLY);
+ }
+ xfchdir(root_fd);
+ xchroot(".");
+ /*close(root_fd);*/
+ /*root_fd = -1;*/
+ }
+
+ if (wd_fd >= 0) {
+ xfchdir(wd_fd);
+ /*close(wd_fd);*/
+ /*wd_fd = -1;*/
+ }
+
+ /*
+ * Entering the pid namespace implies forking unless it's been
+ * explicitly requested by the user not to.
+ */
+ if (!(opts & OPT_nofork) && (opts & OPT_pid)) {
+ pid_t pid = xvfork();
+ if (pid > 0) {
+ /* Parent */
+ int exit_status = wait_for_exitstatus(pid);
+ if (WIFSIGNALED(exit_status))
+ kill_myself_with_sig(WTERMSIG(exit_status));
+ return WEXITSTATUS(exit_status);
+ }
+ /* Child continues */
+ }
+
+ if (opts & OPT_setgid) {
+ if (setgroups(0, NULL) < 0 && setgroups_failed)
+ bb_perror_msg_and_die("setgroups");
+ xsetgid(gid);
+ }
+ if (opts & OPT_setuid)
+ xsetuid(uid);
+
+ if (*argv) {
+ BB_EXECVP_or_die(argv);
+ }
+
+ run_shell(getenv("SHELL"), /*login:*/ 1, NULL, NULL);
+}
projects / oweals / busybox.git / commitdiff