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nspawn: rework how /run/host/ is set up 

Let's find the right os-release file on the host side, and only mount
the one that matters, i.e. /etc/os-release if it exists and
/usr/lib/os-release otherwise. Use the fixed path /run/host/os-release
for that.

Let's also mount /run/host as a bind mount on itself before we set up
/run/host, and let's mount it MS_RDONLY after we are done, so that it
remains immutable as a whole.
This commit is contained in:
Lennart Poettering 2020-07-23 16:49:13 +02:00
parent 62b0ee9eb1
commit d64e32c245
3 changed files with 53 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

66
src/nspawn/nspawn-mount.c
View File

@ -563,15 +563,16 @@ int mount_all(const char *dest,
MOUNT_FATAL|MOUNT_MKDIR },
{ "tmpfs", "/run", "tmpfs", "mode=755" TMPFS_LIMITS_RUN, MS_NOSUID|MS_NODEV|MS_STRICTATIME,
MOUNT_FATAL|MOUNT_MKDIR },
{ "/usr/lib/os-release", "/run/host/usr/lib/os-release", NULL, NULL, MS_BIND,
MOUNT_FATAL|MOUNT_MKDIR|MOUNT_TOUCH }, /* As per kernel interface requirements, bind mount first (creating mount points) and make read-only later */
{ NULL, "/run/host/usr/lib/os-release", NULL, NULL, MS_BIND|MS_RDONLY|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_REMOUNT,
0 },
{ "/etc/os-release", "/run/host/etc/os-release", NULL, NULL, MS_BIND,
MOUNT_MKDIR|MOUNT_TOUCH },
{ NULL, "/run/host/etc/os-release", NULL, NULL, MS_BIND|MS_RDONLY|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_REMOUNT,
0 },
{ "/run/host", "/run/host", NULL, NULL, MS_BIND,
MOUNT_FATAL|MOUNT_MKDIR|MOUNT_PREFIX_ROOT }, /* Prepare this so that we can make it read-only when we are done */
{ "/etc/os-release", "/run/host/os-release", NULL, NULL, MS_BIND,
MOUNT_TOUCH }, /* As per kernel interface requirements, bind mount first (creating mount points) and make read-only later */
{ "/usr/lib/os-release", "/run/host/os-release", NULL, NULL, MS_BIND,
MOUNT_FATAL }, /* If /etc/os-release doesn't exist use the version in /usr/lib as fallback */
{ NULL, "/run/host/os-release", NULL, NULL, MS_BIND|MS_RDONLY|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_REMOUNT,
MOUNT_FATAL },
{ NULL, "/run/host", NULL, NULL, MS_BIND|MS_RDONLY|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_REMOUNT,
MOUNT_FATAL|MOUNT_IN_USERNS },
#if HAVE_SELINUX
{ "/sys/fs/selinux", "/sys/fs/selinux", NULL, NULL, MS_BIND,
MOUNT_MKDIR }, /* Bind mount first (mkdir/chown the mount point in case /sys/ is mounted as minimal skeleton tmpfs) */
@ -589,9 +590,9 @@ int mount_all(const char *dest,
int r;
for (k = 0; k < ELEMENTSOF(mount_table); k++) {
_cleanup_free_ char *where = NULL, *options = NULL;
const char *o;
_cleanup_free_ char *where = NULL, *options = NULL, *prefixed = NULL;
bool fatal = FLAGS_SET(mount_table[k].mount_settings, MOUNT_FATAL);
const char *o;
if (in_userns != FLAGS_SET(mount_table[k].mount_settings, MOUNT_IN_USERNS))
continue;
@ -616,20 +617,9 @@ int mount_all(const char *dest,
return log_error_errno(r, "Failed to detect whether %s is a mount point: %m", where);
if (r > 0)
continue;
/* Shortcut for optional bind mounts: if the source can't be found skip ahead to avoid creating
* empty and unused directories. */
if (!fatal && FLAGS_SET(mount_table[k].mount_settings, MOUNT_MKDIR) && FLAGS_SET(mount_table[k].flags, MS_BIND)) {
r = access(mount_table[k].what, F_OK);
if (r < 0) {
if (errno == ENOENT)
continue;
return log_error_errno(errno, "Failed to stat %s: %m", mount_table[k].what);
}
}
}
if (FLAGS_SET(mount_table[k].mount_settings, MOUNT_MKDIR)) {
if ((mount_table[k].mount_settings & (MOUNT_MKDIR|MOUNT_TOUCH)) != 0) {
uid_t u = (use_userns && !in_userns) ? uid_shift : UID_INVALID;
if (FLAGS_SET(mount_table[k].mount_settings, MOUNT_TOUCH))
@ -647,13 +637,17 @@ int mount_all(const char *dest,
if (r != -EROFS)
continue;
}
if (FLAGS_SET(mount_table[k].mount_settings, MOUNT_TOUCH)) {
r = touch(where);
if (r < 0 && r != -EEXIST) {
if (fatal)
return log_error_errno(r, "Failed to create mount point %s: %m", where);
log_debug_errno(r, "Failed to create mount point %s: %m", where);
}
}
if (FLAGS_SET(mount_table[k].mount_settings, MOUNT_TOUCH)) {
r = touch(where);
if (r < 0 && r != -EEXIST) {
if (fatal && r != -EROFS)
return log_error_errno(r, "Failed to create file %s: %m", where);
log_debug_errno(r, "Failed to create file %s: %m", where);
if (r != -EROFS)
continue;
}
}
@ -666,8 +660,18 @@ int mount_all(const char *dest,
o = options;
}
if (FLAGS_SET(mount_table[k].mount_settings, MOUNT_PREFIX_ROOT)) {
/* Optionally prefix the mount source with the root dir. This is useful in bind
* mounts to be created within the container image before we transition into it. Note
* that MOUNT_IN_USERNS is run after we transitioned hence prefixing is not ncessary
* for those. */
r = chase_symlinks(mount_table[k].what, dest, CHASE_PREFIX_ROOT, &prefixed, NULL);
if (r < 0)
return log_error_errno(r, "Failed to resolve %s/%s: %m", dest, mount_table[k].what);
}
r = mount_verbose(fatal ? LOG_ERR : LOG_DEBUG,
mount_table[k].what,
prefixed ?: mount_table[k].what,
where,
mount_table[k].type,
mount_table[k].flags,

1
src/nspawn/nspawn-mount.h
View File

@ -18,6 +18,7 @@ typedef enum MountSettingsMask {
MOUNT_NON_ROOT_ONLY = 1 << 7, /* if set, only non-root mounts are mounted */
MOUNT_MKDIR = 1 << 8, /* if set, make directory to mount over first */
MOUNT_TOUCH = 1 << 9, /* if set, touch file to mount over first */
MOUNT_PREFIX_ROOT = 1 << 10,/* if set, prefix the source path with the container's root directory */
} MountSettingsMask;
typedef enum CustomMountType {

21
test/units/testsuite-13.sh
View File

@ -66,12 +66,25 @@ if [ -n "${ID:+set}" ] && [ "${ID}" != "${container_host_id}" ]; then exit 1; fi
if [ -n "${VERSION_ID:+set}" ] && [ "${VERSION_ID}" != "${container_host_version_id}" ]; then exit 1; fi
if [ -n "${BUILD_ID:+set}" ] && [ "${BUILD_ID}" != "${container_host_build_id}" ]; then exit 1; fi
if [ -n "${VARIANT_ID:+set}" ] && [ "${VARIANT_ID}" != "${container_host_variant_id}" ]; then exit 1; fi
cd /tmp; (cd /run/host/usr/lib; md5sum os-release) | md5sum -c
if echo test >> /run/host/usr/lib/os-release; then exit 1; fi
if echo test >> /run/host/etc/os-release; then exit 1; fi
cd /tmp; (cd /run/host; md5sum os-release) | md5sum -c
if echo test >> /run/host/os-release; then exit 1; fi
'
systemd-nspawn --register=no -D /testsuite-13.nc-container --bind=/etc/os-release:/tmp/os-release /bin/sh -x -e -c "$_cmd"
local _os_release_source="/etc/os-release"
if [ ! -r "${_os_release_source}" ]; then
_os_release_source="/usr/lib/os-release"
elif [ -L "${_os_release_source}" ] && rm /etc/os-release; then
# Ensure that /etc always wins if available
cp /usr/lib/os-release /etc
echo MARKER=1 >> /etc/os-release
fi
systemd-nspawn --register=no -D /testsuite-13.nc-container --bind="${_os_release_source}":/tmp/os-release /bin/sh -x -e -c "$_cmd"
if grep -q MARKER /etc/os-release; then
rm /etc/os-release
ln -s ../usr/lib/os-release /etc/os-release
fi
}
function run {