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core: deduplicate identical dm-verity ExtensionImages=

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It turns out OverlayFS doesn't handle gracefully when the same source is
specified multiple times in lowerdir= and it fails with ELOOP:

Failed to mount overlay (type overlay) on /run/systemd/mount-rootfs/opt (MS_RDONLY "lowerdir=/run/systemd/unit-extensions/1/opt:/run/systemd/unit-extensions/0/opt:/run/systemd/mount-rootfs/opt"): Too many levels of symbolic links

This happens even if we mount each image in a different internal mount
path, as OverlayFS will resolve it and look for the backing device, which
will be the same device mapper entity, and return a hard error.
This error does not appear if dm-verity is not used, so it is very
confusing for users, and unnecessary.

When mounting ExtensionImages, check if an image is dm-veritied,
and drop duplicates if the root hashes match, to avoid this user-unfriendly
hard error.
This commit is contained in:
Luca Boccassi 2024-06-04 16:00:03 +01:00
parent b268a71069
commit a1a40297db
6 changed files with 85 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

47
src/core/namespace.c
View File

@ -112,6 +112,7 @@ typedef struct MountEntry {
unsigned n_followed;
LIST_HEAD(MountOptions, image_options_const);
char **overlay_layers;
VeritySettings verity;
} MountEntry;
typedef struct MountList {
@ -343,6 +344,7 @@ static void mount_entry_done(MountEntry *p) {
p->source_malloc = mfree(p->source_malloc);
p->options_malloc = mfree(p->options_malloc);
p->overlay_layers = strv_free(p->overlay_layers);
verity_settings_done(&p->verity);
}
static void mount_list_done(MountList *ml) {
@ -505,6 +507,7 @@ static int append_extensions(
/* First, prepare a mount for each image, but these won't be visible to the unit, instead
* they will be mounted in our propagate directory, and used as a source for the overlay. */
for (size_t i = 0; i < n_mount_images; i++) {
_cleanup_(verity_settings_done) VeritySettings verity = VERITY_SETTINGS_DEFAULT;
_cleanup_(pick_result_done) PickResult result = PICK_RESULT_NULL;
_cleanup_free_ char *mount_point = NULL;
const MountImage *m = mount_images + i;
@ -523,6 +526,10 @@ static int append_extensions(
"No matching entry in .v/ directory %s found.",
m->source);
r = verity_settings_load(&verity, result.path, /* root_hash_path= */ NULL, /* root_hash_sig_path= */ NULL);
if (r < 0)
return log_debug_errno(r, "Failed to check verity root hash of %s: %m", result.path);
if (asprintf(&mount_point, "%s/unit-extensions/%zu", private_namespace_dir, i) < 0)
return -ENOMEM;
@ -547,6 +554,7 @@ static int append_extensions(
.source_malloc = TAKE_PTR(result.path),
.mode = MOUNT_EXTENSION_IMAGE,
.has_prefix = true,
.verity = TAKE_GENERIC(verity, VeritySettings, VERITY_SETTINGS_DEFAULT),
};
}
@ -787,6 +795,36 @@ static int prefix_where_needed(MountList *ml, const char *root_directory) {
return 0;
}
static bool verity_has_later_duplicates(MountList *ml, const MountEntry *needle) {
assert(ml);
assert(needle);
assert(needle >= ml->mounts && needle < ml->mounts + ml->n_mounts);
assert(needle->mode == MOUNT_EXTENSION_IMAGE);
if (needle->verity.root_hash_size == 0)
return false;
/* Overlayfs rejects supplying the same directory inode twice as determined by filesystem UUID and
* file handle in lowerdir=, even if they are mounted on different paths, as it resolves each mount
* to its source filesystem, so drop duplicates, and keep the last one. This only covers non-DDI
* verity images. Note that the list is ordered, so we only check for the reminder of the list for
* each item, rather than the full list from the beginning, as any earlier duplicates will have
* already been pruned. */
for (const MountEntry *m = needle + 1; m < ml->mounts + ml->n_mounts; m++) {
if (m->mode != MOUNT_EXTENSION_IMAGE)
continue;
if (memcmp_nn(m->verity.root_hash,
m->verity.root_hash_size,
needle->verity.root_hash,
needle->verity.root_hash_size) == 0)
return true;
}
return false;
}
static void drop_duplicates(MountList *ml) {
MountEntry *f, *t, *previous;
@ -810,6 +848,12 @@ static void drop_duplicates(MountList *ml) {
continue;
}
if (f->mode == MOUNT_EXTENSION_IMAGE && verity_has_later_duplicates(ml, f)) {
log_debug("Skipping duplicate extension image %s", mount_entry_source(f));
mount_entry_done(f);
continue;
}
*t = *f;
previous = t;
t++;
@ -1347,7 +1391,7 @@ static int mount_mqueuefs(const MountEntry *m) {
}
static int mount_image(
const MountEntry *m,
MountEntry *m,
const char *root_directory,
const ImagePolicy *image_policy) {
@ -1387,6 +1431,7 @@ static int mount_image(
host_os_release_sysext_level,
host_os_release_confext_level,
/* required_sysext_scope= */ NULL,
&m->verity,
/* ret_image= */ NULL);
if (r == -ENOENT && m->ignore)
return 0;

31
src/shared/dissect-image.c
View File

@ -4034,11 +4034,12 @@ int verity_dissect_and_mount(
const char *required_host_os_release_sysext_level,
const char *required_host_os_release_confext_level,
const char *required_sysext_scope,
VeritySettings *verity,
DissectedImage **ret_image) {
_cleanup_(loop_device_unrefp) LoopDevice *loop_device = NULL;
_cleanup_(dissected_image_unrefp) DissectedImage *dissected_image = NULL;
_cleanup_(verity_settings_done) VeritySettings verity = VERITY_SETTINGS_DEFAULT;
_cleanup_(verity_settings_done) VeritySettings local_verity = VERITY_SETTINGS_DEFAULT;
DissectImageFlags dissect_image_flags;
bool relax_extension_release_check;
int r;
@ -4050,13 +4051,19 @@ int verity_dissect_and_mount(
relax_extension_release_check = mount_options_relax_extension_release_checks(options);
/* We might get an FD for the image, but we use the original path to look for the dm-verity files */
r = verity_settings_load(&verity, src, NULL, NULL);
if (r < 0)
return log_debug_errno(r, "Failed to load root hash: %m");
/* We might get an FD for the image, but we use the original path to look for the dm-verity files.
* The caller might also give us a pre-loaded VeritySettings, in which case we just use it. It will
* also be extended, as dissected_image_load_verity_sig_partition() is invoked. */
if (!verity) {
r = verity_settings_load(&local_verity, src, NULL, NULL);
if (r < 0)
return log_debug_errno(r, "Failed to load root hash: %m");
verity = &local_verity;
}
dissect_image_flags =
(verity.data_path ? DISSECT_IMAGE_NO_PARTITION_TABLE : 0) |
(verity->data_path ? DISSECT_IMAGE_NO_PARTITION_TABLE : 0) |
(relax_extension_release_check ? DISSECT_IMAGE_RELAX_EXTENSION_CHECK : 0) |
DISSECT_IMAGE_ADD_PARTITION_DEVICES |
DISSECT_IMAGE_PIN_PARTITION_DEVICES |
@ -4068,7 +4075,7 @@ int verity_dissect_and_mount(
src_fd >= 0 ? FORMAT_PROC_FD_PATH(src_fd) : src,
/* open_flags= */ -1,
/* sector_size= */ UINT32_MAX,
verity.data_path ? 0 : LO_FLAGS_PARTSCAN,
verity->data_path ? 0 : LO_FLAGS_PARTSCAN,
LOCK_SH,
&loop_device);
if (r < 0)
@ -4076,16 +4083,16 @@ int verity_dissect_and_mount(
r = dissect_loop_device(
loop_device,
&verity,
verity,
options,
image_policy,
dissect_image_flags,
&dissected_image);
/* No partition table? Might be a single-filesystem image, try again */
if (!verity.data_path && r == -ENOPKG)
if (!verity->data_path && r == -ENOPKG)
r = dissect_loop_device(
loop_device,
&verity,
verity,
options,
image_policy,
dissect_image_flags | DISSECT_IMAGE_NO_PARTITION_TABLE,
@ -4093,14 +4100,14 @@ int verity_dissect_and_mount(
if (r < 0)
return log_debug_errno(r, "Failed to dissect image: %m");
r = dissected_image_load_verity_sig_partition(dissected_image, loop_device->fd, &verity);
r = dissected_image_load_verity_sig_partition(dissected_image, loop_device->fd, verity);
if (r < 0)
return r;
r = dissected_image_decrypt(
dissected_image,
NULL,
&verity,
verity,
dissect_image_flags);
if (r < 0)
return log_debug_errno(r, "Failed to decrypt dissected image: %m");

2
src/shared/dissect-image.h
View File

@ -226,7 +226,7 @@ bool dissected_image_verity_sig_ready(const DissectedImage *image, PartitionDesi
int mount_image_privately_interactively(const char *path, const ImagePolicy *image_policy, DissectImageFlags flags, char **ret_directory, int *ret_dir_fd, LoopDevice **ret_loop_device);
int verity_dissect_and_mount(int src_fd, const char *src, const char *dest, const MountOptions *options, const ImagePolicy *image_policy, const char *required_host_os_release_id, const char *required_host_os_release_version_id, const char *required_host_os_release_sysext_level, const char *required_host_os_release_confext_level, const char *required_sysext_scope, DissectedImage **ret_image);
int verity_dissect_and_mount(int src_fd, const char *src, const char *dest, const MountOptions *options, const ImagePolicy *image_policy, const char *required_host_os_release_id, const char *required_host_os_release_version_id, const char *required_host_os_release_sysext_level, const char *required_host_os_release_confext_level, const char *required_sysext_scope, VeritySettings *verity, DissectedImage **ret_image);
int dissect_fstype_ok(const char *fstype);

2
src/shared/mount-util.c
View File

@ -941,6 +941,7 @@ static int mount_in_namespace_legacy(
/* required_host_os_release_sysext_level= */ NULL,
/* required_host_os_release_confext_level= */ NULL,
/* required_sysext_scope= */ NULL,
/* verity= */ NULL,
/* ret_image= */ NULL);
else
r = mount_follow_verbose(LOG_DEBUG, FORMAT_PROC_FD_PATH(chased_src_fd), mount_tmp, NULL, MS_BIND, NULL);
@ -1166,6 +1167,7 @@ static int mount_in_namespace(
/* required_host_os_release_sysext_level= */ NULL,
/* required_host_os_release_confext_level= */ NULL,
/* required_sysext_scope= */ NULL,
/* verity= */ NULL,
&img);
if (r < 0)
return log_debug_errno(

1
test/TEST-50-DISSECT/test.sh
View File

@ -37,6 +37,7 @@ test_append_files() {
inst_binary mksquashfs
inst_binary unsquashfs
inst_binary pkcheck
inst_binary veritysetup
install_verity_minimal
}

16
test/units/TEST-50-DISSECT.dissect.sh
View File

@ -389,6 +389,22 @@ systemd-run -P \
--property RootImage="$MINIMAL_IMAGE.raw" \
"${BIND_LOG_SOCKETS[@]}" \
cat /etc/systemd/system/some_file | grep -q -F "MARKER_CONFEXT_123"
# Check that two identical verity images at different paths do not fail with -ELOOP from OverlayFS
mkdir -p /tmp/loop
cp /tmp/app0.raw /tmp/loop/app0.raw
veritysetup format /tmp/loop/app0.raw /tmp/loop/app0.verity --root-hash-file /tmp/loop/app0.roothash
cp /tmp/loop/app0.raw /tmp/loop/app0_copy.raw
cp /tmp/loop/app0.verity /tmp/loop/app0_copy.verity
cp /tmp/loop/app0.roothash /tmp/loop/app0_copy.roothash
systemd-run -P \
--property ExtensionImages=/tmp/loop/app0.raw \
--property ExtensionImages=/tmp/loop/app0_copy.raw \
--property RootImage="$MINIMAL_IMAGE.raw" \
"${BIND_LOG_SOCKETS[@]}" \
cat /opt/script0.sh | grep -q -F "extension-release.app0"
rm -rf /tmp/loop/
# Check that using a symlink to NAME-VERSION.raw works as long as the symlink has the correct name NAME.raw
mkdir -p /tmp/symlink-test/
cp /tmp/app-nodistro.raw /tmp/symlink-test/app-nodistro-v1.raw