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process-util: add a new FORK_MOUNTNS_SLAVE flag for safe_fork() 

We already have a flag for creating a new mount namespace for the child.
Let's add an extension to that: a new FORK_MOUNTNFS_SLAVE flag. When
used in combination will mark all mounts in the child namespace as
MS_SLAVE so that the child can freely mount or unmount stuff but it
won't leak into the parent.
This commit is contained in:
Lennart Poettering 2018-03-23 20:52:46 +01:00
parent 03bcb6d408
commit e2047ba9ed
3 changed files with 13 additions and 5 deletions
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11
src/basic/process-util.c
View File

@ -17,6 +17,7 @@
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/personality.h>
#include <sys/prctl.h>
#include <sys/types.h>
@ -1344,6 +1345,16 @@ int safe_fork_full(
}
}
if ((flags & (FORK_NEW_MOUNTNS|FORK_MOUNTNS_SLAVE)) == (FORK_NEW_MOUNTNS|FORK_MOUNTNS_SLAVE)) {
/* Optionally, make sure we never propagate mounts to the host. */
if (mount(NULL, "/", NULL, MS_SLAVE | MS_REC, NULL) < 0) {
log_full_errno(prio, errno, "Failed to remount root directory as MS_SLAVE: %m");
_exit(EXIT_FAILURE);
}
}
if (flags & FORK_CLOSE_ALL_FDS) {
/* Close the logs here in case it got reopened above, as close_all_fds() would close them for us */
log_close();

1
src/basic/process-util.h
View File

@ -163,6 +163,7 @@ typedef enum ForkFlags {
FORK_LOG = 1U << 5,
FORK_WAIT = 1U << 6,
FORK_NEW_MOUNTNS = 1U << 7,
FORK_MOUNTNS_SLAVE = 1U << 8,
} ForkFlags;
int safe_fork_full(const char *name, const int except_fds[], size_t n_except_fds, ForkFlags flags, pid_t *ret_pid);

6
src/shared/dissect-image.c
View File

@ -1278,14 +1278,10 @@ int dissected_image_acquire_metadata(DissectedImage *m) {
if (r < 0)
goto finish;
r = safe_fork("(sd-dissect)", FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_NEW_MOUNTNS, &child);
r = safe_fork("(sd-dissect)", FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_NEW_MOUNTNS|FORK_MOUNTNS_SLAVE, &child);
if (r < 0)
goto finish;
if (r == 0) {
/* Make sure we never propagate to the host */
if (mount(NULL, "/", NULL, MS_SLAVE | MS_REC, NULL) < 0)
_exit(EXIT_FAILURE);
r = dissected_image_mount(m, t, UID_INVALID, DISSECT_IMAGE_READ_ONLY|DISSECT_IMAGE_MOUNT_ROOT_ONLY|DISSECT_IMAGE_VALIDATE_OS);
if (r < 0) {
log_debug_errno(r, "Failed to mount dissected image: %m");