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switch-root: use MS_REC for /run, unless we are soft-rebooting

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There are applications that rely on mounts under /run surviving the
switch from initrd to rootfs, so use MS_REC unless we are soft
rebooting.

Follow-up for 7c764d4599

Fixes https://github.com/systemd/systemd/issues/28452
This commit is contained in:
Luca Boccassi 2023-07-22 22:45:16 +01:00
parent acfff02c8f
commit b12d41a8bb
3 changed files with 21 additions and 10 deletions
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3
src/core/main.c
View File

@ -1884,7 +1884,8 @@ static int do_reexecute(
if (switch_root_dir) {
r = switch_root(/* new_root= */ switch_root_dir,
/* old_root_after= */ NULL,
/* flags= */ objective == MANAGER_SWITCH_ROOT ? SWITCH_ROOT_DESTROY_OLD_ROOT : 0);
/* flags= */ (objective == MANAGER_SWITCH_ROOT ? SWITCH_ROOT_DESTROY_OLD_ROOT : 0) |
(objective == MANAGER_SOFT_REBOOT ? SWITCH_ROOT_SKIP_RECURSIVE_RUN : 0));
if (r < 0)
log_error_errno(r, "Failed to switch root, trying to continue: %m");
}

23
src/shared/switch-root.c
View File

@ -30,17 +30,23 @@ int switch_root(const char *new_root,
const char *old_root_after, /* path below the new root, where to place the old root after the transition; may be NULL to unmount it */
SwitchRootFlags flags) {
/* Stuff mounted below /run we don't save on soft reboot, as it might have lost its relevance, i.e.
* credentials, removable media and such, we rather want that the new boot mounts this fresh.
* But on the switch from initrd we do use MS_REC, as it is expected that mounts set up in /run
* are maintained. */
unsigned long run_mount_flags = MS_BIND|(!FLAGS_SET(flags, SWITCH_ROOT_SKIP_RECURSIVE_RUN) ? MS_REC : 0);
struct {
const char *path;
unsigned long mount_flags;
bool skip_if_run_is_rec; /* For child mounts of /run, if it's moved recursively no need to handle */
} transfer_table[] = {
{ "/dev", MS_BIND|MS_REC }, /* Recursive, because we want to save the original /dev/shm + /dev/pts and similar */
{ "/sys", MS_BIND|MS_REC }, /* Similar, we want to retain various API VFS, or the cgroupv1 /sys/fs/cgroup/ tree */
{ "/proc", MS_BIND|MS_REC }, /* Similar */
{ "/run", MS_BIND }, /* Stuff mounted below this we don't save, as it might have lost its relevance, i.e. credentials, removable media and such, we rather want that the new boot mounts this fresh */
{ SYSTEM_CREDENTIALS_DIRECTORY, MS_BIND }, /* Credentials passed into the system should survive */
{ ENCRYPTED_SYSTEM_CREDENTIALS_DIRECTORY, MS_BIND }, /* Similar */
{ "/run/host", MS_BIND|MS_REC }, /* Host supplied hierarchy should also survive */
{ "/dev", MS_BIND|MS_REC, false }, /* Recursive, because we want to save the original /dev/shm + /dev/pts and similar */
{ "/sys", MS_BIND|MS_REC, false }, /* Similar, we want to retain various API VFS, or the cgroupv1 /sys/fs/cgroup/ tree */
{ "/proc", MS_BIND|MS_REC, false }, /* Similar */
{ "/run", run_mount_flags, false }, /* Recursive except on soft reboot, see above */
{ SYSTEM_CREDENTIALS_DIRECTORY, MS_BIND, true }, /* Credentials passed into the system should survive */
{ ENCRYPTED_SYSTEM_CREDENTIALS_DIRECTORY, MS_BIND, true }, /* Similar */
{ "/run/host", MS_BIND|MS_REC, true }, /* Host supplied hierarchy should also survive */
};
_cleanup_close_ int old_root_fd = -EBADF, new_root_fd = -EBADF;
@ -112,6 +118,9 @@ int switch_root(const char *new_root,
FOREACH_ARRAY(transfer, transfer_table, ELEMENTSOF(transfer_table)) {
_cleanup_free_ char *chased = NULL;
if (transfer->skip_if_run_is_rec && !FLAGS_SET(flags, SWITCH_ROOT_SKIP_RECURSIVE_RUN))
continue;
if (access(transfer->path, F_OK) < 0) {
log_debug_errno(errno, "Path '%s' to move to target root directory, not found, ignoring: %m", transfer->path);
continue;

5
src/shared/switch-root.h
View File

@ -4,8 +4,9 @@
#include <stdbool.h>
typedef enum SwitchRootFlags {
SWITCH_ROOT_DESTROY_OLD_ROOT = 1 << 0, /* rm -rf old root when switching – under the condition that it is backed by non-persistent tmpfs/ramfs/… */
SWITCH_ROOT_DONT_SYNC = 1 << 1, /* don't call sync() immediately before switching root */
SWITCH_ROOT_DESTROY_OLD_ROOT = 1 << 0, /* rm -rf old root when switching – under the condition that it is backed by non-persistent tmpfs/ramfs/… */
SWITCH_ROOT_DONT_SYNC = 1 << 1, /* don't call sync() immediately before switching root */
SWITCH_ROOT_SKIP_RECURSIVE_RUN = 1 << 2, /* move /run without MS_REC */
} SwitchRootFlags;
int switch_root(const char *new_root, const char *old_root_after, SwitchRootFlags flags);