unshare: new applet
function old new delta unshare_main - 873 +873 .rodata 154444 155131 +687 packed_usage 30329 30520 +191 unshare_longopts - 106 +106 mount_namespaces - 99 +99 mount_or_die - 51 +51 ns_list - 48 +48 wait_for_exitstatus - 41 +41 opt_str - 17 +17 applet_names 2510 2518 +8 applet_main 2912 2920 +8 applet_suid 91 92 +1 applet_install_loc 182 183 +1 ------------------------------------------------------------------------------ (add/remove: 8/0 grow/shrink: 6/0 up/down: 2131/0) Total: 2131 bytes text data bss dec hex filename 826110 4070 9080 839260 cce5c busybox_old 827961 4078 9080 841119 cd59f busybox_unstripped Signed-off-by: Bartosz Golaszewski <bartekgola@gmail.com> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Bartosz Golaszewski
committed by
Denys Vlasenko
Denys Vlasenko
parent
52977a7d60
commit
29b33b63d4
380
util-linux/unshare.c
Normal file
380
util-linux/unshare.c
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@@ -0,0 +1,380 @@
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/* vi: set sw=4 ts=4: */
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/*
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* Mini unshare implementation for busybox.
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*
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* Copyright (C) 2016 by Bartosz Golaszewski <bartekgola@gmail.com>
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*
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* Licensed under GPLv2 or later, see file LICENSE in this source tree.
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*/
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//config:config UNSHARE
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//config: bool "unshare"
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//config: default y
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//config: depends on LONG_OPTS && !NOMMU
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//config: select PLATFORM_LINUX
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//config: help
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//config: Run program with some namespaces unshared from parent.
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// depends on LONG_OPTS: it is awkward to exclude code which handles --propagation
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// and --setgroups based on LONG_OPTS, so instead applet requires LONG_OPTS.
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// depends on !NOMMU: we need fork()
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//applet:IF_UNSHARE(APPLET(unshare, BB_DIR_USR_BIN, BB_SUID_DROP))
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//kbuild:lib-$(CONFIG_UNSHARE) += unshare.o
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//usage:#define unshare_trivial_usage
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//usage: "[OPTIONS] [PROG [ARGS]]"
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//usage:#define unshare_full_usage "\n"
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//usage: "\n -m, --mount[=FILE] Unshare mount namespace"
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//usage: "\n -u, --uts[=FILE] Unshare UTS namespace (hostname etc.)"
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//usage: "\n -i, --ipc[=FILE] Unshare System V IPC namespace"
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//usage: "\n -n, --net[=FILE] Unshare network namespace"
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//usage: "\n -p, --pid[=FILE] Unshare PID namespace"
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//usage: "\n -U, --user[=FILE} Unshare user namespace"
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//usage: "\n -f, --fork Fork before execing PROG"
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//usage: "\n -r, --map-root-user Map current user to root (implies -u)"
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//usage: "\n --mount-proc[=DIR] Mount /proc filesystem first (implies -m)"
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//usage: "\n --propagation slave|shared|private|unchanged"
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//usage: "\n Modify mount propagation in mount namespace"
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//usage: "\n --setgroups allow|deny Control the setgroups syscall in user namespaces"
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#include <sched.h>
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#include <sys/mount.h>
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#include "libbb.h"
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static void mount_or_die(const char *source, const char *target,
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const char *fstype, unsigned long mountflags)
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{
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if (mount(source, target, fstype, mountflags, NULL)) {
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bb_perror_msg_and_die("can't mount %s on %s (flags:0x%lx)",
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source, target, mountflags);
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/* fstype is always either NULL or "proc".
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* "proc" is only used to mount /proc.
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* No need to clutter up error message with fstype,
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* it is easily deductible.
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*/
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}
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}
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// TODO: move to libbb
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static int wait_for_exitstatus(pid_t pid)
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{
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int exit_status, n;
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n = safe_waitpid(pid, &exit_status, 0);
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if (n < 0)
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bb_perror_msg_and_die("waitpid");
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return exit_status;
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}
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/*
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* Longest possible path to a procfs file used in unshare. Must be able to
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* contain the '/proc/' string, the '/ns/user' string which is the longest
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* namespace name and a 32-bit integer representing the process ID.
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*/
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#define PATH_PROC_SETGROUPS "/proc/self/setgroups"
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#define PATH_PROC_UIDMAP "/proc/self/uid_map"
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#define PATH_PROC_GIDMAP "/proc/self/gid_map"
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struct namespace_descr {
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int flag;
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const char nsfile4[4];
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};
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struct namespace_ctx {
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char *path;
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};
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enum {
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OPT_mount = 1 << 0,
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OPT_uts = 1 << 1,
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OPT_ipc = 1 << 2,
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OPT_network = 1 << 3,
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OPT_pid = 1 << 4,
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OPT_user = 1 << 5, /* OPT_user, NS_USR_POS, and ns_list[] index must match! */
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OPT_fork = 1 << 6,
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OPT_map_root = 1 << 7,
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OPT_mount_proc = 1 << 8,
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OPT_propagation = 1 << 9,
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OPT_setgroups = 1 << 10,
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};
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enum {
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NS_MNT_POS = 0,
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NS_UTS_POS,
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NS_IPC_POS,
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NS_NET_POS,
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NS_PID_POS,
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NS_USR_POS, /* OPT_user, NS_USR_POS, and ns_list[] index must match! */
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NS_COUNT,
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};
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static const struct namespace_descr ns_list[] = {
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{ CLONE_NEWNS, "mnt" },
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{ CLONE_NEWUTS, "uts" },
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{ CLONE_NEWIPC, "ipc" },
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{ CLONE_NEWNET, "net" },
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{ CLONE_NEWPID, "pid" },
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{ CLONE_NEWUSER, "user" }, /* OPT_user, NS_USR_POS, and ns_list[] index must match! */
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};
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/*
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* Upstream unshare doesn't support short options for --mount-proc,
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* --propagation, --setgroups.
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* Optional arguments (namespace mountpoints) exist only for long opts,
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* we are forced to use "fake" letters for them.
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* '+': stop at first non-option.
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*/
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static const char opt_str[] = "+muinpU""fr""\xfd::""\xfe:""\xff:";
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static const char unshare_longopts[] ALIGN1 =
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"mount\0" Optional_argument "\xf0"
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"uts\0" Optional_argument "\xf1"
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"ipc\0" Optional_argument "\xf2"
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"network\0" Optional_argument "\xf3"
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"pid\0" Optional_argument "\xf4"
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"user\0" Optional_argument "\xf5"
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"fork\0" No_argument "f"
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"map-root-user\0" No_argument "r"
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"mount-proc\0" Optional_argument "\xfd"
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"propagation\0" Required_argument "\xfe"
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"setgroups\0" Required_argument "\xff"
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;
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/* Ugly-looking string reuse trick */
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#define PRIVATE_STR "private\0""unchanged\0""shared\0""slave\0"
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#define PRIVATE_UNCHANGED_SHARED_SLAVE PRIVATE_STR
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static unsigned long parse_propagation(const char *prop_str)
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{
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int i = index_in_strings(PRIVATE_UNCHANGED_SHARED_SLAVE, prop_str);
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if (i < 0)
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bb_error_msg_and_die("unrecognized: --%s=%s", "propagation", prop_str);
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if (i == 0)
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return MS_REC | MS_PRIVATE;
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if (i == 1)
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return 0;
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if (i == 2)
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return MS_REC | MS_SHARED;
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return MS_REC | MS_SLAVE;
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}
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static void mount_namespaces(pid_t pid, struct namespace_ctx *ns_ctx_list)
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{
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const struct namespace_descr *ns;
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struct namespace_ctx *ns_ctx;
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int i;
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for (i = 0; i < NS_COUNT; i++) {
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char nsf[sizeof("/proc/%u/ns/AAAA") + sizeof(int)*3];
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ns = &ns_list[i];
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ns_ctx = &ns_ctx_list[i];
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if (!ns_ctx->path)
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continue;
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sprintf(nsf, "/proc/%u/ns/%.4s", (unsigned)pid, ns->nsfile4);
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mount_or_die(nsf, ns_ctx->path, NULL, MS_BIND);
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}
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}
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int unshare_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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int unshare_main(int argc UNUSED_PARAM, char **argv)
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{
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int i;
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unsigned int opts;
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int unsflags;
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uintptr_t need_mount;
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const char *proc_mnt_target;
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const char *prop_str;
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const char *setgrp_str;
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unsigned long prop_flags;
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uid_t reuid = geteuid();
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gid_t regid = getegid();
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struct fd_pair fdp;
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pid_t child = child; /* for compiler */
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struct namespace_ctx ns_ctx_list[NS_COUNT];
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memset(ns_ctx_list, 0, sizeof(ns_ctx_list));
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proc_mnt_target = "/proc";
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prop_str = PRIVATE_STR;
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setgrp_str = NULL;
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opt_complementary =
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"\xf0""m" /* long opts (via their "fake chars") imply short opts */
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":\xf1""u"
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":\xf2""i"
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":\xf3""n"
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":\xf4""p"
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":\xf5""U"
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":ru" /* --map-root-user or -r implies -u */
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":\xfd""m" /* --mount-proc implies -m */
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;
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applet_long_options = unshare_longopts;
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opts = getopt32(argv, opt_str,
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&proc_mnt_target, &prop_str, &setgrp_str,
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&ns_ctx_list[NS_MNT_POS].path,
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&ns_ctx_list[NS_UTS_POS].path,
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&ns_ctx_list[NS_IPC_POS].path,
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&ns_ctx_list[NS_NET_POS].path,
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&ns_ctx_list[NS_PID_POS].path,
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&ns_ctx_list[NS_USR_POS].path
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);
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argv += optind;
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//bb_error_msg("opts:0x%x", opts);
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//bb_error_msg("mount:%s", ns_ctx_list[NS_MNT_POS].path);
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//bb_error_msg("proc_mnt_target:%s", proc_mnt_target);
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//bb_error_msg("prop_str:%s", prop_str);
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//bb_error_msg("setgrp_str:%s", setgrp_str);
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//exit(1);
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if (setgrp_str) {
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if (strcmp(setgrp_str, "allow") == 0) {
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if (opts & OPT_map_root) {
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bb_error_msg_and_die(
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"--setgroups=allow and --map-root-user "
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"are mutually exclusive"
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);
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}
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} else {
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/* It's not "allow", must be "deny" */
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if (strcmp(setgrp_str, "deny") != 0)
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bb_error_msg_and_die("unrecognized: --%s=%s",
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"setgroups", setgrp_str);
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}
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}
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unsflags = 0;
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need_mount = 0;
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for (i = 0; i < NS_COUNT; i++) {
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const struct namespace_descr *ns = &ns_list[i];
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struct namespace_ctx *ns_ctx = &ns_ctx_list[i];
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if (opts & (1 << i))
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unsflags |= ns->flag;
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need_mount |= (uintptr_t)(ns_ctx->path);
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}
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/* need_mount != 0 if at least one FILE was given */
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prop_flags = MS_REC | MS_PRIVATE;
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/* Silently ignore --propagation if --mount is not requested. */
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if (opts & OPT_mount)
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prop_flags = parse_propagation(prop_str);
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/*
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* Special case: if we were requested to unshare the mount namespace
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* AND to make any namespace persistent (by bind mounting it) we need
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* to spawn a child process which will wait for the parent to call
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* unshare(), then mount parent's namespaces while still in the
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* previous namespace.
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*/
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fdp.wr = -1;
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if (need_mount && (opts & OPT_mount)) {
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/*
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* Can't use getppid() in child, as we can be unsharing the
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* pid namespace.
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*/
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pid_t ppid = getpid();
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xpiped_pair(fdp);
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child = xfork();
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if (child == 0) {
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/* Child */
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close(fdp.wr);
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/* Wait until parent calls unshare() */
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read(fdp.rd, ns_ctx_list, 1); /* ...using bogus buffer */
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/*close(fdp.rd);*/
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/* Mount parent's unshared namespaces. */
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mount_namespaces(ppid, ns_ctx_list);
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return EXIT_SUCCESS;
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}
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/* Parent continues */
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}
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if (unshare(unsflags) != 0)
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bb_perror_msg_and_die("unshare(0x%x)", unsflags);
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if (fdp.wr >= 0) {
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close(fdp.wr); /* Release child */
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/*close(fdp.rd);*/
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}
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if (need_mount) {
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/* Wait for the child to finish mounting the namespaces. */
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if (opts & OPT_mount) {
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int exit_status = wait_for_exitstatus(child);
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if (WIFEXITED(exit_status) &&
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WEXITSTATUS(exit_status) != EXIT_SUCCESS)
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return WEXITSTATUS(exit_status);
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} else {
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/*
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* Regular way - we were requested to mount some other
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* namespaces: mount them after the call to unshare().
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*/
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mount_namespaces(getpid(), ns_ctx_list);
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}
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}
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/*
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* When we're unsharing the pid namespace, it's not the process that
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* calls unshare() that is put into the new namespace, but its first
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* child. The user may want to use this option to spawn a new process
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* that'll become PID 1 in this new namespace.
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*/
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if (opts & OPT_fork) {
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pid_t pid = xfork();
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if (pid > 0) {
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/* Parent */
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int exit_status = wait_for_exitstatus(pid);
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if (WIFSIGNALED(exit_status))
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kill_myself_with_sig(WTERMSIG(exit_status));
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return WEXITSTATUS(exit_status);
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}
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/* Child continues */
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}
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if (opts & OPT_map_root) {
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char uidmap_buf[sizeof("%u 0 1") + sizeof(int)*3];
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/*
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* Since Linux 3.19 unprivileged writing of /proc/self/gid_map
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* has been disabled unless /proc/self/setgroups is written
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* first to permanently disable the ability to call setgroups
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* in that user namespace.
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*/
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xopen_xwrite_close(PATH_PROC_SETGROUPS, "deny");
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sprintf(uidmap_buf, "%u 0 1", (unsigned)reuid);
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xopen_xwrite_close(PATH_PROC_UIDMAP, uidmap_buf);
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sprintf(uidmap_buf, "%u 0 1", (unsigned)regid);
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xopen_xwrite_close(PATH_PROC_GIDMAP, uidmap_buf);
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} else
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if (setgrp_str) {
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/* Write "allow" or "deny" */
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xopen_xwrite_close(PATH_PROC_SETGROUPS, setgrp_str);
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}
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if (opts & OPT_mount) {
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mount_or_die("none", "/", NULL, prop_flags);
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}
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if (opts & OPT_mount_proc) {
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/*
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* When creating a new pid namespace, we might want the pid
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* subdirectories in /proc to remain consistent with the new
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* process IDs. Without --mount-proc the pids in /proc would
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* still reflect the old pid namespace. This is why we make
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* /proc private here and then do a fresh mount.
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*/
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mount_or_die("none", proc_mnt_target, NULL, MS_PRIVATE | MS_REC);
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mount_or_die("proc", proc_mnt_target, "proc", MS_NOSUID | MS_NOEXEC | MS_NODEV);
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}
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if (argv[0]) {
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BB_EXECVP_or_die(argv);
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}
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/* unshare from util-linux 2.27.1, despite not documenting it,
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* runs a login shell (argv0="-sh") if no PROG is given
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*/
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run_shell(getenv("SHELL"), /*login:*/ 1, NULL, NULL);
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}
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