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| -rw-r--r-- | util-linux/unshare.c | 380 |
1 files changed, 380 insertions, 0 deletions
diff --git a/util-linux/unshare.c b/util-linux/unshare.c new file mode 100644 index 0000000..f1a9cdf --- /dev/null +++ b/util-linux/unshare.c @@ -0,0 +1,380 @@ +/* vi: set sw=4 ts=4: */ +/* + * Mini unshare 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 UNSHARE +//config: bool "unshare" +//config: default y +//config: depends on LONG_OPTS && !NOMMU +//config: select PLATFORM_LINUX +//config: help +//config: Run program with some namespaces unshared from parent. + +// depends on LONG_OPTS: it is awkward to exclude code which handles --propagation +// and --setgroups based on LONG_OPTS, so instead applet requires LONG_OPTS. +// depends on !NOMMU: we need fork() + +//applet:IF_UNSHARE(APPLET(unshare, BB_DIR_USR_BIN, BB_SUID_DROP)) + +//kbuild:lib-$(CONFIG_UNSHARE) += unshare.o + +//usage:#define unshare_trivial_usage +//usage: "[OPTIONS] [PROG [ARGS]]" +//usage:#define unshare_full_usage "\n" +//usage: "\n -m, --mount[=FILE] Unshare mount namespace" +//usage: "\n -u, --uts[=FILE] Unshare UTS namespace (hostname etc.)" +//usage: "\n -i, --ipc[=FILE] Unshare System V IPC namespace" +//usage: "\n -n, --net[=FILE] Unshare network namespace" +//usage: "\n -p, --pid[=FILE] Unshare PID namespace" +//usage: "\n -U, --user[=FILE} Unshare user namespace" +//usage: "\n -f, --fork Fork before execing PROG" +//usage: "\n -r, --map-root-user Map current user to root (implies -u)" +//usage: "\n --mount-proc[=DIR] Mount /proc filesystem first (implies -m)" +//usage: "\n --propagation slave|shared|private|unchanged" +//usage: "\n Modify mount propagation in mount namespace" +//usage: "\n --setgroups allow|deny Control the setgroups syscall in user namespaces" + +#include <sched.h> +#include <sys/mount.h> +#include "libbb.h" + +static void mount_or_die(const char *source, const char *target, + const char *fstype, unsigned long mountflags) +{ + if (mount(source, target, fstype, mountflags, NULL)) { + bb_perror_msg_and_die("can't mount %s on %s (flags:0x%lx)", + source, target, mountflags); + /* fstype is always either NULL or "proc". + * "proc" is only used to mount /proc. + * No need to clutter up error message with fstype, + * it is easily deductible. + */ + } +} + +// TODO: move to libbb +static int wait_for_exitstatus(pid_t pid) +{ + int exit_status, n; + + n = safe_waitpid(pid, &exit_status, 0); + if (n < 0) + bb_perror_msg_and_die("waitpid"); + return exit_status; +} + +/* + * Longest possible path to a procfs file used in unshare. Must be able to + * contain the '/proc/' string, the '/ns/user' string which is the longest + * namespace name and a 32-bit integer representing the process ID. + */ +#define PATH_PROC_SETGROUPS "/proc/self/setgroups" +#define PATH_PROC_UIDMAP "/proc/self/uid_map" +#define PATH_PROC_GIDMAP "/proc/self/gid_map" + +struct namespace_descr { + int flag; + const char nsfile4[4]; +}; + +struct namespace_ctx { + char *path; +}; + +enum { + OPT_mount = 1 << 0, + OPT_uts = 1 << 1, + OPT_ipc = 1 << 2, + OPT_network = 1 << 3, + OPT_pid = 1 << 4, + OPT_user = 1 << 5, /* OPT_user, NS_USR_POS, and ns_list[] index must match! */ + OPT_fork = 1 << 6, + OPT_map_root = 1 << 7, + OPT_mount_proc = 1 << 8, + OPT_propagation = 1 << 9, + OPT_setgroups = 1 << 10, +}; +enum { + NS_MNT_POS = 0, + NS_UTS_POS, + NS_IPC_POS, + NS_NET_POS, + NS_PID_POS, + NS_USR_POS, /* OPT_user, NS_USR_POS, and ns_list[] index must match! */ + NS_COUNT, +}; +static const struct namespace_descr ns_list[] = { + { CLONE_NEWNS, "mnt" }, + { CLONE_NEWUTS, "uts" }, + { CLONE_NEWIPC, "ipc" }, + { CLONE_NEWNET, "net" }, + { CLONE_NEWPID, "pid" }, + { CLONE_NEWUSER, "user" }, /* OPT_user, NS_USR_POS, and ns_list[] index must match! */ +}; + +/* + * Upstream unshare doesn't support short options for --mount-proc, + * --propagation, --setgroups. + * Optional arguments (namespace mountpoints) exist only for long opts, + * we are forced to use "fake" letters for them. + * '+': stop at first non-option. + */ +static const char opt_str[] = "+muinpU""fr""\xfd::""\xfe:""\xff:"; +static const char unshare_longopts[] ALIGN1 = + "mount\0" Optional_argument "\xf0" + "uts\0" Optional_argument "\xf1" + "ipc\0" Optional_argument "\xf2" + "network\0" Optional_argument "\xf3" + "pid\0" Optional_argument "\xf4" + "user\0" Optional_argument "\xf5" + "fork\0" No_argument "f" + "map-root-user\0" No_argument "r" + "mount-proc\0" Optional_argument "\xfd" + "propagation\0" Required_argument "\xfe" + "setgroups\0" Required_argument "\xff" +; + +/* Ugly-looking string reuse trick */ +#define PRIVATE_STR "private\0""unchanged\0""shared\0""slave\0" +#define PRIVATE_UNCHANGED_SHARED_SLAVE PRIVATE_STR + +static unsigned long parse_propagation(const char *prop_str) +{ + int i = index_in_strings(PRIVATE_UNCHANGED_SHARED_SLAVE, prop_str); + if (i < 0) + bb_error_msg_and_die("unrecognized: --%s=%s", "propagation", prop_str); + if (i == 0) + return MS_REC | MS_PRIVATE; + if (i == 1) + return 0; + if (i == 2) + return MS_REC | MS_SHARED; + return MS_REC | MS_SLAVE; +} + +static void mount_namespaces(pid_t pid, struct namespace_ctx *ns_ctx_list) +{ + const struct namespace_descr *ns; + struct namespace_ctx *ns_ctx; + int i; + + for (i = 0; i < NS_COUNT; i++) { + char nsf[sizeof("/proc/%u/ns/AAAA") + sizeof(int)*3]; + + ns = &ns_list[i]; + ns_ctx = &ns_ctx_list[i]; + if (!ns_ctx->path) + continue; + sprintf(nsf, "/proc/%u/ns/%.4s", (unsigned)pid, ns->nsfile4); + mount_or_die(nsf, ns_ctx->path, NULL, MS_BIND); + } +} + +int unshare_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; +int unshare_main(int argc UNUSED_PARAM, char **argv) +{ + int i; + unsigned int opts; + int unsflags; + uintptr_t need_mount; + const char *proc_mnt_target; + const char *prop_str; + const char *setgrp_str; + unsigned long prop_flags; + uid_t reuid = geteuid(); + gid_t regid = getegid(); + struct fd_pair fdp; + pid_t child = child; /* for compiler */ + struct namespace_ctx ns_ctx_list[NS_COUNT]; + + memset(ns_ctx_list, 0, sizeof(ns_ctx_list)); + proc_mnt_target = "/proc"; + prop_str = PRIVATE_STR; + setgrp_str = NULL; + + opt_complementary = + "\xf0""m" /* long opts (via their "fake chars") imply short opts */ + ":\xf1""u" + ":\xf2""i" + ":\xf3""n" + ":\xf4""p" + ":\xf5""U" + ":ru" /* --map-root-user or -r implies -u */ + ":\xfd""m" /* --mount-proc implies -m */ + ; + applet_long_options = unshare_longopts; + opts = getopt32(argv, opt_str, + &proc_mnt_target, &prop_str, &setgrp_str, + &ns_ctx_list[NS_MNT_POS].path, + &ns_ctx_list[NS_UTS_POS].path, + &ns_ctx_list[NS_IPC_POS].path, + &ns_ctx_list[NS_NET_POS].path, + &ns_ctx_list[NS_PID_POS].path, + &ns_ctx_list[NS_USR_POS].path + ); + argv += optind; + //bb_error_msg("opts:0x%x", opts); + //bb_error_msg("mount:%s", ns_ctx_list[NS_MNT_POS].path); + //bb_error_msg("proc_mnt_target:%s", proc_mnt_target); + //bb_error_msg("prop_str:%s", prop_str); + //bb_error_msg("setgrp_str:%s", setgrp_str); + //exit(1); + + if (setgrp_str) { + if (strcmp(setgrp_str, "allow") == 0) { + if (opts & OPT_map_root) { + bb_error_msg_and_die( + "--setgroups=allow and --map-root-user " + "are mutually exclusive" + ); + } + } else { + /* It's not "allow", must be "deny" */ + if (strcmp(setgrp_str, "deny") != 0) + bb_error_msg_and_die("unrecognized: --%s=%s", + "setgroups", setgrp_str); + } + } + + unsflags = 0; + need_mount = 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 (opts & (1 << i)) + unsflags |= ns->flag; + + need_mount |= (uintptr_t)(ns_ctx->path); + } + /* need_mount != 0 if at least one FILE was given */ + + prop_flags = MS_REC | MS_PRIVATE; + /* Silently ignore --propagation if --mount is not requested. */ + if (opts & OPT_mount) + prop_flags = parse_propagation(prop_str); + + /* + * Special case: if we were requested to unshare the mount namespace + * AND to make any namespace persistent (by bind mounting it) we need + * to spawn a child process which will wait for the parent to call + * unshare(), then mount parent's namespaces while still in the + * previous namespace. + */ + fdp.wr = -1; + if (need_mount && (opts & OPT_mount)) { + /* + * Can't use getppid() in child, as we can be unsharing the + * pid namespace. + */ + pid_t ppid = getpid(); + + xpiped_pair(fdp); + + child = xfork(); + if (child == 0) { + /* Child */ + close(fdp.wr); + + /* Wait until parent calls unshare() */ + read(fdp.rd, ns_ctx_list, 1); /* ...using bogus buffer */ + /*close(fdp.rd);*/ + + /* Mount parent's unshared namespaces. */ + mount_namespaces(ppid, ns_ctx_list); + return EXIT_SUCCESS; + } + /* Parent continues */ + } + + if (unshare(unsflags) != 0) + bb_perror_msg_and_die("unshare(0x%x)", unsflags); + + if (fdp.wr >= 0) { + close(fdp.wr); /* Release child */ + /*close(fdp.rd);*/ + } + + if (need_mount) { + /* Wait for the child to finish mounting the namespaces. */ + if (opts & OPT_mount) { + int exit_status = wait_for_exitstatus(child); + if (WIFEXITED(exit_status) && + WEXITSTATUS(exit_status) != EXIT_SUCCESS) + return WEXITSTATUS(exit_status); + } else { + /* + * Regular way - we were requested to mount some other + * namespaces: mount them after the call to unshare(). + */ + mount_namespaces(getpid(), ns_ctx_list); + } + } + + /* + * When we're unsharing the pid namespace, it's not the process that + * calls unshare() that is put into the new namespace, but its first + * child. The user may want to use this option to spawn a new process + * that'll become PID 1 in this new namespace. + */ + if (opts & OPT_fork) { + pid_t pid = xfork(); + 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_map_root) { + char uidmap_buf[sizeof("%u 0 1") + sizeof(int)*3]; + + /* + * Since Linux 3.19 unprivileged writing of /proc/self/gid_map + * has been disabled unless /proc/self/setgroups is written + * first to permanently disable the ability to call setgroups + * in that user namespace. + */ + xopen_xwrite_close(PATH_PROC_SETGROUPS, "deny"); + sprintf(uidmap_buf, "%u 0 1", (unsigned)reuid); + xopen_xwrite_close(PATH_PROC_UIDMAP, uidmap_buf); + sprintf(uidmap_buf, "%u 0 1", (unsigned)regid); + xopen_xwrite_close(PATH_PROC_GIDMAP, uidmap_buf); + } else + if (setgrp_str) { + /* Write "allow" or "deny" */ + xopen_xwrite_close(PATH_PROC_SETGROUPS, setgrp_str); + } + + if (opts & OPT_mount) { + mount_or_die("none", "/", NULL, prop_flags); + } + + if (opts & OPT_mount_proc) { + /* + * When creating a new pid namespace, we might want the pid + * subdirectories in /proc to remain consistent with the new + * process IDs. Without --mount-proc the pids in /proc would + * still reflect the old pid namespace. This is why we make + * /proc private here and then do a fresh mount. + */ + mount_or_die("none", proc_mnt_target, NULL, MS_PRIVATE | MS_REC); + mount_or_die("proc", proc_mnt_target, "proc", MS_NOSUID | MS_NOEXEC | MS_NODEV); + } + + if (argv[0]) { + BB_EXECVP_or_die(argv); + } + /* unshare from util-linux 2.27.1, despite not documenting it, + * runs a login shell (argv0="-sh") if no PROG is given + */ + run_shell(getenv("SHELL"), /*login:*/ 1, NULL, NULL); +} |