diff options
| -rw-r--r-- | src/nspawn/nspawn.c | 226 |
1 files changed, 189 insertions, 37 deletions
diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c index a3190545fa..c330456ff9 100644 --- a/src/nspawn/nspawn.c +++ b/src/nspawn/nspawn.c @@ -22,7 +22,9 @@ #endif #include <errno.h> #include <getopt.h> +#include <grp.h> #include <linux/loop.h> +#include <pwd.h> #include <sched.h> #ifdef HAVE_SECCOMP #include <seccomp.h> @@ -102,6 +104,11 @@ #include "user-util.h" #include "util.h" +/* Note that devpts's gid= parameter parses GIDs as signed values, hence we stay away from the upper half of the 32bit + * UID range here */ +#define UID_SHIFT_PICK_MIN ((uid_t) UINT32_C(0x00080000)) +#define UID_SHIFT_PICK_MAX ((uid_t) UINT32_C(0x6FFF0000)) + typedef enum ContainerStatus { CONTAINER_TERMINATED, CONTAINER_REBOOTED @@ -174,9 +181,10 @@ static char *arg_image = NULL; static VolatileMode arg_volatile_mode = VOLATILE_NO; static ExposePort *arg_expose_ports = NULL; static char **arg_property = NULL; -static uid_t arg_uid_shift = UID_INVALID, arg_uid_range = 0x10000U; static bool arg_userns = false; static bool arg_userns_chown = false; +static uid_t arg_uid_shift = UID_INVALID, arg_uid_range = 0x10000U; +static bool arg_uid_shift_pick = false; static int arg_kill_signal = 0; static bool arg_unified_cgroup_hierarchy = false; static SettingsMask arg_settings_mask = 0; @@ -275,9 +283,15 @@ static int custom_mounts_prepare(void) { for (i = 0; i < arg_n_custom_mounts; i++) { CustomMount *m = &arg_custom_mounts[i]; - if (arg_userns && arg_uid_shift == UID_INVALID && path_equal(m->destination, "/")) { - log_error("--private-users with automatic UID shift may not be combined with custom root mounts."); - return -EINVAL; + if (path_equal(m->destination, "/") && arg_userns) { + + if (arg_userns_chown) { + log_error("--private-users-chown may not be combined with custom root mounts."); + return -EINVAL; + } else if (arg_uid_shift == UID_INVALID) { + log_error("--private-users with automatic UID shift may not be combined with custom root mounts."); + return -EINVAL; + } } if (m->type != CUSTOM_MOUNT_OVERLAY) @@ -806,25 +820,37 @@ static int parse_argv(int argc, char *argv[]) { _cleanup_free_ char *buffer = NULL; const char *range, *shift; - range = strchr(optarg, ':'); - if (range) { - buffer = strndup(optarg, range - optarg); - if (!buffer) - return log_oom(); - shift = buffer; - - range++; - if (safe_atou32(range, &arg_uid_range) < 0 || arg_uid_range <= 0) { - log_error("Failed to parse UID range: %s", range); + if (streq(optarg, "pick")) { + arg_uid_shift = UID_INVALID; + arg_uid_range = 0x10000U; + arg_uid_shift_pick = true; + } else { + range = strchr(optarg, ':'); + if (range) { + buffer = strndup(optarg, range - optarg); + if (!buffer) + return log_oom(); + shift = buffer; + + range++; + if (safe_atou32(range, &arg_uid_range) < 0 || arg_uid_range <= 0) { + log_error("Failed to parse UID range: %s", range); + return -EINVAL; + } + } else + shift = optarg; + + if (parse_uid(shift, &arg_uid_shift) < 0) { + log_error("Failed to parse UID: %s", optarg); return -EINVAL; } - } else - shift = optarg; - if (parse_uid(shift, &arg_uid_shift) < 0) { - log_error("Failed to parse UID: %s", optarg); - return -EINVAL; + arg_uid_shift_pick = false; } + } else { + arg_uid_shift = UID_INVALID; + arg_uid_range = 0x10000U; + arg_uid_shift_pick = false; } arg_userns = true; @@ -902,6 +928,9 @@ static int parse_argv(int argc, char *argv[]) { if (arg_share_system) arg_register = false; + if (arg_uid_shift_pick) + arg_userns_chown = true; + if (arg_start_mode != START_PID1 && arg_share_system) { log_error("--boot and --share-system may not be combined."); return -EINVAL; @@ -2501,7 +2530,6 @@ static int determine_uid_shift(const char *directory) { return -EINVAL; } - log_info("Using user namespaces with base " UID_FMT " and range " UID_FMT ".", arg_uid_shift, arg_uid_range); return 0; } @@ -2789,6 +2817,7 @@ static int outer_child( return r; if (arg_userns) { + /* Let the parent know which UID shift we read from the image */ l = send(uid_shift_socket, &arg_uid_shift, sizeof(arg_uid_shift), MSG_NOSIGNAL); if (l < 0) return log_error_errno(errno, "Failed to send UID shift: %m"); @@ -2796,6 +2825,22 @@ static int outer_child( log_error("Short write while sending UID shift."); return -EIO; } + + if (arg_uid_shift_pick) { + /* When we are supposed to pick the UID shift, the parent will check now whether the UID shift + * we just read from the image is available. If yes, it will send the UID shift back to us, if + * not it will pick a different one, and send it back to us. */ + + l = recv(uid_shift_socket, &arg_uid_shift, sizeof(arg_uid_shift), 0); + if (l < 0) + return log_error_errno(errno, "Failed to recv UID shift: %m"); + if (l != sizeof(arg_uid_shift)) { + log_error("Short read while recieving UID shift."); + return -EIO; + } + } + + log_info("Selected user namespace base " UID_FMT " and range " UID_FMT ".", arg_uid_shift, arg_uid_range); } /* Turn directory into bind mount */ @@ -2925,6 +2970,61 @@ static int outer_child( return 0; } +static int uid_shift_pick(uid_t *shift, LockFile *ret_lock_file) { + unsigned n_tries = 100; + uid_t candidate; + int r; + + assert(shift); + assert(ret_lock_file); + assert(arg_uid_shift_pick); + assert(arg_uid_range == 0x10000U); + + candidate = *shift; + + (void) mkdir("/run/systemd/nspawn-uid", 0755); + + for (;;) { + char lock_path[strlen("/run/systemd/nspawn-uid/") + DECIMAL_STR_MAX(uid_t) + 1]; + _cleanup_release_lock_file_ LockFile lf = LOCK_FILE_INIT; + + if (--n_tries <= 0) + return -EBUSY; + + if (candidate < UID_SHIFT_PICK_MIN || candidate > UID_SHIFT_PICK_MAX) + goto next; + if ((candidate & UINT32_C(0xFFFF)) != 0) + goto next; + + xsprintf(lock_path, "/run/systemd/nspawn-uid/" UID_FMT, candidate); + r = make_lock_file(lock_path, LOCK_EX|LOCK_NB, &lf); + if (r == -EBUSY) /* Range already taken by another nspawn instance */ + goto next; + if (r < 0) + return r; + + /* Make some superficial checks whether the range is currently known in the user database */ + if (getpwuid(candidate)) + goto next; + if (getpwuid(candidate + UINT32_C(0xFFFE))) + goto next; + if (getgrgid(candidate)) + goto next; + if (getgrgid(candidate + UINT32_C(0xFFFE))) + goto next; + + *ret_lock_file = lf; + lf = (struct LockFile) LOCK_FILE_INIT; + *shift = candidate; + return 0; + + next: + random_bytes(&candidate, sizeof(candidate)); + candidate = (candidate % (UID_SHIFT_PICK_MAX - UID_SHIFT_PICK_MIN)) + UID_SHIFT_PICK_MIN; + candidate &= (uid_t) UINT32_C(0xFFFF0000); + } +} + static int setup_uid_map(pid_t pid) { char uid_map[strlen("/proc//uid_map") + DECIMAL_STR_MAX(uid_t) + 1], line[DECIMAL_STR_MAX(uid_t)*3+3+1]; int r; @@ -3394,20 +3494,42 @@ int main(int argc, char *argv[]) { } for (;;) { - _cleanup_close_pair_ int kmsg_socket_pair[2] = { -1, -1 }, rtnl_socket_pair[2] = { -1, -1 }, - pid_socket_pair[2] = { -1, -1 }, uuid_socket_pair[2] = { -1, -1 }, uid_shift_socket_pair[2] = { -1, -1 }; - ContainerStatus container_status; - _cleanup_(barrier_destroy) Barrier barrier = BARRIER_NULL; static const struct sigaction sa = { .sa_handler = nop_signal_handler, .sa_flags = SA_NOCLDSTOP, }; - int ifi = 0; - ssize_t l; + + _cleanup_release_lock_file_ LockFile uid_shift_lock = LOCK_FILE_INIT; + _cleanup_close_ int etc_passwd_lock = -1; + _cleanup_close_pair_ int + kmsg_socket_pair[2] = { -1, -1 }, + rtnl_socket_pair[2] = { -1, -1 }, + pid_socket_pair[2] = { -1, -1 }, + uuid_socket_pair[2] = { -1, -1 }, + uid_shift_socket_pair[2] = { -1, -1 }; + _cleanup_(barrier_destroy) Barrier barrier = BARRIER_NULL; _cleanup_(sd_event_unrefp) sd_event *event = NULL; _cleanup_(pty_forward_freep) PTYForward *forward = NULL; _cleanup_(sd_netlink_unrefp) sd_netlink *rtnl = NULL; + ContainerStatus container_status; char last_char = 0; + int ifi = 0; + ssize_t l; + + if (arg_uid_shift_pick) { + /* When we shall pick the UID/GID range, let's first lock /etc/passwd, so that we can safely + * check with getpwuid() if the specific user already exists. Note that /etc might be + * read-only, in which case this will fail with EROFS. But that's really OK, as in that case we + * can be reasonably sure that no users are going to be added. Note that getpwuid() checks are + * really just an extra safety net. We kinda assume that the UID range we allocate from is + * really ours. */ + + etc_passwd_lock = take_etc_passwd_lock(NULL); + if (etc_passwd_lock < 0 && etc_passwd_lock != -EROFS) { + log_error_errno(r, "Failed to take /etc/passwd lock: %m"); + goto finish; + } + } r = barrier_create(&barrier); if (r < 0) { @@ -3511,6 +3633,43 @@ int main(int argc, char *argv[]) { uuid_socket_pair[1] = safe_close(uuid_socket_pair[1]); uid_shift_socket_pair[1] = safe_close(uid_shift_socket_pair[1]); + if (arg_userns) { + /* The child just let us know the UID shift it might have read from the image. */ + l = recv(uid_shift_socket_pair[0], &arg_uid_shift, sizeof(arg_uid_shift), 0); + if (l < 0) { + r = log_error_errno(errno, "Failed to read UID shift: %m"); + goto finish; + } + if (l != sizeof(arg_uid_shift)) { + log_error("Short read while reading UID shift."); + r = EIO; + goto finish; + } + + if (arg_uid_shift_pick) { + /* If we are supposed to pick the UID shift, let's try to use the shift read from the + * image, but if that's already in use, pick a new one, and report back to the child, + * which one we now picked. */ + + r = uid_shift_pick(&arg_uid_shift, &uid_shift_lock); + if (r < 0) { + log_error_errno(r, "Failed to pick suitable UID/GID range: %m"); + goto finish; + } + + l = send(uid_shift_socket_pair[0], &arg_uid_shift, sizeof(arg_uid_shift), MSG_NOSIGNAL); + if (l < 0) { + r = log_error_errno(errno, "Failed to send UID shift: %m"); + goto finish; + } + if (l != sizeof(arg_uid_shift)) { + log_error("Short write while writing UID shift."); + r = -EIO; + goto finish; + } + } + } + /* Wait for the outer child. */ r = wait_for_terminate_and_warn("namespace helper", pid, NULL); if (r < 0) @@ -3554,17 +3713,6 @@ int main(int argc, char *argv[]) { goto finish; } - l = recv(uid_shift_socket_pair[0], &arg_uid_shift, sizeof(arg_uid_shift), 0); - if (l < 0) { - r = log_error_errno(errno, "Failed to read UID shift: %m"); - goto finish; - } - if (l != sizeof(arg_uid_shift)) { - log_error("Short read while reading UID shift."); - r = EIO; - goto finish; - } - r = setup_uid_map(pid); if (r < 0) goto finish; @@ -3662,6 +3810,10 @@ int main(int argc, char *argv[]) { goto finish; } + /* At this point we have made use of the UID we picked, and thus nss-mymachines will make them appear + * in getpwuid(), thus we can release the /etc/passwd lock. */ + etc_passwd_lock = safe_close(etc_passwd_lock); + sd_notifyf(false, "READY=1\n" "STATUS=Container running.\n" |