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Merge pull request #13184 from poettering/nspawn-usr-root

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Allow "systemd-nspawn -D / --volatile=yes" to work
This commit is contained in:
Lennart Poettering 2019-07-29 13:40:23 +02:00 committed by GitHub
parent 88bc86fcf8 6f83d3d149
commit a13c64b1d7
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GPG key ID: 4AEE18F83AFDEB23
2 changed files with 65 additions and 18 deletions
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37
src/nspawn/nspawn.c
View file

@ -3264,8 +3264,24 @@ static int outer_child(
"Selected user namespace base " UID_FMT " and range " UID_FMT ".", arg_uid_shift, arg_uid_range);
}
if (!dissected_image) {
/* Turn directory into bind mount */
if (path_equal(directory, "/")) {
/* If the directory we shall boot is the host, let's operate on a bind mount at a different
* place, so that we can make changes to its mount structure (for example, to implement
* --volatile=) without this interfering with our ability to access files such as
* /etc/localtime to copy into the container. Note that we use a fixed place for this
* (instead of a temporary directory, since we are living in our own mount namspace here
* already, and thus don't need to be afraid of colliding with anyone else's mounts).*/
(void) mkdir_p("/run/systemd/nspawn-root", 0755);
r = mount_verbose(LOG_ERR, "/", "/run/systemd/nspawn-root", NULL, MS_BIND|MS_REC, NULL);
if (r < 0)
return r;
directory = "/run/systemd/nspawn-root";
} else if (!dissected_image) {
/* Turn directory into bind mount (we need that so that we can move the bind mount to root
* later on). */
r = mount_verbose(LOG_ERR, directory, directory, NULL, MS_BIND|MS_REC, NULL);
if (r < 0)
return r;
@ -4018,7 +4034,7 @@ static int load_settings(void) {
p = file_in_same_dir(arg_image, fn);
if (!p)
return log_oom();
} else if (arg_directory) {
} else if (arg_directory && !path_equal(arg_directory, "/")) {
p = file_in_same_dir(arg_directory, fn);
if (!p)
return log_oom();
@ -4740,8 +4756,12 @@ static int run(int argc, char *argv[]) {
if (arg_directory) {
assert(!arg_image);
if (path_equal(arg_directory, "/") && !arg_ephemeral) {
log_error("Spawning container on root directory is not supported. Consider using --ephemeral.");
/* Safety precaution: let's not allow running images from the live host OS image, as long as
* /var from the host will propagate into container dynamically (because bad things happen if
* two systems write to the same /var). Let's allow it for the special cases where /var is
* either copied (i.e. --ephemeral) or replaced (i.e. --volatile=yes|state). */
if (path_equal(arg_directory, "/") && !(arg_ephemeral || IN_SET(arg_volatile_mode, VOLATILE_YES, VOLATILE_STATE))) {
log_error("Spawning container on root directory is not supported. Consider using --ephemeral, --volatile=yes or --volatile=state.");
r = -EINVAL;
goto finish;
}
@ -4770,7 +4790,9 @@ static int run(int argc, char *argv[]) {
goto finish;
}
r = image_path_lock(np, (arg_read_only ? LOCK_SH : LOCK_EX) | LOCK_NB, &tree_global_lock, &tree_local_lock);
/* We take an exclusive lock on this image, since it's our private, ephemeral copy
* only owned by us and noone else. */
r = image_path_lock(np, LOCK_EX|LOCK_NB, &tree_global_lock, &tree_local_lock);
if (r < 0) {
log_error_errno(r, "Failed to lock %s: %m", np);
goto finish;
@ -4890,7 +4912,8 @@ static int run(int argc, char *argv[]) {
goto finish;
}
r = image_path_lock(np, (arg_read_only ? LOCK_SH : LOCK_EX) | LOCK_NB, &tree_global_lock, &tree_local_lock);
/* Always take an exclusive lock on our own ephemeral copy. */
r = image_path_lock(np, LOCK_EX|LOCK_NB, &tree_global_lock, &tree_local_lock);
if (r < 0) {
r = log_error_errno(r, "Failed to create image lock: %m");
goto finish;

46
src/shared/machine-image.c
View file

@ -989,28 +989,52 @@ int image_path_lock(const char *path, int operation, LockFile *global, LockFile
_cleanup_free_ char *p = NULL;
LockFile t = LOCK_FILE_INIT;
struct stat st;
bool exclusive;
int r;
assert(path);
assert(global);
assert(local);
/* Locks an image path. This actually creates two locks: one
* "local" one, next to the image path itself, which might be
* shared via NFS. And another "global" one, in /run, that
* uses the device/inode number. This has the benefit that we
* can even lock a tree that is a mount point, correctly. */
/* Locks an image path. This actually creates two locks: one "local" one, next to the image path
* itself, which might be shared via NFS. And another "global" one, in /run, that uses the
* device/inode number. This has the benefit that we can even lock a tree that is a mount point,
* correctly. */
if (!path_is_absolute(path))
return -EINVAL;
switch (operation & (LOCK_SH|LOCK_EX)) {
case LOCK_SH:
exclusive = false;
break;
case LOCK_EX:
exclusive = true;
break;
default:
return -EINVAL;
}
if (getenv_bool("SYSTEMD_NSPAWN_LOCK") == 0) {
*local = *global = (LockFile) LOCK_FILE_INIT;
return 0;
}
if (path_equal(path, "/"))
return -EBUSY;
/* Prohibit taking exclusive locks on the host image. We can't allow this, since we ourselves are
* running off it after all, and we don't want any images to manipulate the host image. We make an
* exception for shared locks however: we allow those (and make them NOPs since there's no point in
* taking them if there can't be exclusive locks). Strictly speaking these are questionable as well,
* since it means changes made to the host might propagate to the container as they happen (and a
* shared lock kinda suggests that no changes happen at all while it is in place), but it's too
* useful not to allow read-only containers off the host root, hence let's support this, and trust
* the user to do the right thing with this. */
if (path_equal(path, "/")) {
if (exclusive)
return -EBUSY;
*local = *global = (LockFile) LOCK_FILE_INIT;
return 0;
}
if (stat(path, &st) >= 0) {
if (S_ISBLK(st.st_mode))
@ -1024,12 +1048,12 @@ int image_path_lock(const char *path, int operation, LockFile *global, LockFile
return -ENOMEM;
}
/* For block devices we don't need the "local" lock, as the major/minor lock above should be sufficient, since
* block devices are device local anyway. */
if (!path_startswith(path, "/dev")) {
/* For block devices we don't need the "local" lock, as the major/minor lock above should be
* sufficient, since block devices are host local anyway. */
if (!path_startswith(path, "/dev/")) {
r = make_lock_file_for(path, operation, &t);
if (r < 0) {
if ((operation & LOCK_SH) && r == -EROFS)
if (!exclusive && r == -EROFS)
log_debug_errno(r, "Failed to create shared lock for '%s', ignoring: %m", path);
else
return r;