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Diffstat (limited to 'src/nspawn/nspawn.c')
-rw-r--r--src/nspawn/nspawn.c226
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"
generated by cgit v1.2.3-54-g00ecf (git 2.45.2) at 2024-12-04 09:45:58 +0000