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shared/install: reuse the standard symlink verification subroutine

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We save a few lines, but the important thing is that we don't have two
different implementations with slightly different rules used for enablement
and loading. Fixes #22000.

Tested with:
- the report in #22000, it now says:
$ SYSTEMD_LOG_LEVEL=debug systemctl --root=/ enable test.service
Suspicious symlink /etc/systemd/system/test.service→/etc/systemd/system/myown.d/test.service, treating as alias.
unit_file_resolve_symlink: self-alias: /etc/systemd/system/test.service → test.service, ignoring.
running_in_chroot(): Permission denied
Suspicious symlink /etc/systemd/system/test.service→/etc/systemd/system/myown.d/test.service, treating as alias.
unit_file_resolve_symlink: self-alias: /etc/systemd/system/test.service → test.service, ignoring.
Failed to enable unit, refusing to operate on linked unit file test.service

- a symlink to /dev/null:
...
unit_file_resolve_symlink: linked unit file: /etc/systemd/system/test3.service → /dev/null
Failed to enable unit, unit /etc/systemd/system/test3.service is masked.

- the same from the host:
...
unit_file_resolve_symlink: linked unit file: /var/lib/machines/rawhide/etc/systemd/system/test3.service → /var/lib/machines/rawhide/dev/null
Failed to enable unit, unit /var/lib/machines/rawhide/etc/systemd/system/test3.service is masked.

- through the manager:
$ sudo systemctl enable test.service
Failed to enable unit: Refusing to operate on alias name or linked unit file: test.service
$ sudo systemctl enable test3.service
Failed to enable unit: Unit file /etc/systemd/system/test3.service is masked.

As seen in the first example, the warning is repeated. This is because we call
the lookup logic twice: first for sysv-compat, and then again for real. I think
that since this is only for broken setups, and when sysv-compat is enabled, and
in an infrequent manual operation, at debug level, this is OK.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2022-03-04 18:47:31 +01:00
parent 48542eac39
commit 047d37dc3d
3 changed files with 76 additions and 78 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

70
src/basic/unit-file.c
View File

@ -259,27 +259,50 @@ static int directory_name_is_valid(const char *name) {
return false;
}
static int unit_file_resolve_symlink(
int unit_file_resolve_symlink(
const char *root_dir,
char **search_path,
const char *dir,
int dirfd,
const char *filename,
bool resolve_destination_target,
char **ret_destination) {
_cleanup_free_ char *target = NULL, *simplified = NULL, *dst = NULL;
_cleanup_free_ char *target = NULL, *simplified = NULL, *dst = NULL, *_dir = NULL, *_filename = NULL;
int r;
assert(dir);
assert(dirfd >= 0);
/* This can be called with either dir+dirfd valid and filename just a name,
* or !dir && dirfd==AT_FDCWD, and filename being a full path.
*
* If resolve_destination_target is true, an absolute path will be returned.
* If not, an absolute path is returned for linked unit files, and a relative
* path otherwise. */
assert(filename);
assert(ret_destination);
assert(dir || path_is_absolute(filename));
assert(dirfd >= 0 || dirfd == AT_FDCWD);
r = readlinkat_malloc(dirfd, filename, &target);
if (r < 0)
return log_warning_errno(r, "Failed to read symlink %s%s%s: %m",
dir, dir ? "/" : "", filename);
if (!dir) {
r = path_extract_directory(filename, &_dir);
if (r < 0)
return r;
dir = _dir;
r = path_extract_filename(filename, &_filename);
if (r < 0)
return r;
if (r == O_DIRECTORY)
return log_warning_errno(SYNTHETIC_ERRNO(EISDIR),
"Unexpected path to a directory \"%s\", refusing.", filename);
filename = _filename;
}
bool is_abs = path_is_absolute(target);
if (root_dir || !is_abs) {
char *target_abs = path_join(is_abs ? root_dir : dir, target);
@ -295,24 +318,36 @@ static int unit_file_resolve_symlink(
return log_warning_errno(r, "Failed to resolve symlink %s/%s pointing to %s: %m",
dir, filename, target);
assert(path_is_absolute(simplified));
/* Check if the symlink goes outside of our search path.
* If yes, it's a linked unit file or mask, and we don't care about the target name.
* Let's just store the link source directly.
* If not, let's verify that it's a good symlink. */
* If yes, it's a linked unit file or mask, and we don't care about the target name
* when loading units, and we return the link *source* (resolve_destination_target == false);
* When this is called for installation purposes, we want the final destination,
* so we return the *target*.
*
* Otherwise, let's verify that it's a good alias.
*/
const char *tail = path_startswith_strv(simplified, search_path);
if (!tail) {
log_debug("Linked unit file: %s/%s → %s", dir, filename, simplified);
dst = path_join(dir, filename);
if (!dst)
return log_oom();
if (resolve_destination_target)
dst = TAKE_PTR(simplified);
else {
dst = path_join(dir, filename);
if (!dst)
return log_oom();
}
} else {
r = path_extract_filename(simplified, &dst);
_cleanup_free_ char *target_name = NULL;
r = path_extract_filename(simplified, &target_name);
if (r < 0)
return r;
bool self_alias = streq(dst, filename);
bool self_alias = streq(target_name, filename);
if (is_path(tail))
log_full(self_alias ? LOG_DEBUG : LOG_WARNING,
@ -323,13 +358,15 @@ static int unit_file_resolve_symlink(
if (r < 0)
return r;
if (self_alias)
/* A self-alias that has no effect */
if (self_alias && !resolve_destination_target)
/* A self-alias that has no effect when loading, let's just ignore it. */
return log_debug_errno(SYNTHETIC_ERRNO(ELOOP),
"Unit file self-alias: %s/%s → %s, ignoring.",
dir, filename, dst);
dir, filename, target_name);
log_debug("Unit file alias: %s/%s → %s", dir, filename, dst);
log_debug("Unit file alias: %s/%s → %s", dir, filename, target_name);
dst = resolve_destination_target ? TAKE_PTR(simplified) : TAKE_PTR(target_name);
}
*ret_destination = TAKE_PTR(dst);
@ -473,6 +510,7 @@ int unit_file_build_name_map(
r = unit_file_resolve_symlink(lp->root_dir, lp->search_path,
*dir, dirfd(d), de->d_name,
/* resolve_destination_target= */ false,
&dst);
if (r == -ENOMEM)
return r;

10
src/basic/unit-file.h
View File

@ -44,6 +44,16 @@ int unit_symlink_name_compatible(const char *symlink, const char *target, bool i
int unit_validate_alias_symlink_and_warn(const char *filename, const char *target);
bool lookup_paths_timestamp_hash_same(const LookupPaths *lp, uint64_t timestamp_hash, uint64_t *ret_new);
int unit_file_resolve_symlink(
const char *root_dir,
char **search_path,
const char *dir,
int dirfd,
const char *filename,
bool resolve_destination_target,
char **ret_destination);
int unit_file_build_name_map(
const LookupPaths *lp,
uint64_t *cache_timestamp_hash,

74
src/shared/install.c
View File

@ -1335,76 +1335,26 @@ static int unit_file_load_or_readlink(
const char *path,
const LookupPaths *lp,
SearchFlags flags) {
_cleanup_free_ char *resolved = NULL;
int r;
r = unit_file_load(c, info, path, lp->root_dir, flags);
if (r != -ELOOP || (flags & SEARCH_DROPIN))
return r;
r = chase_symlinks(path, lp->root_dir, CHASE_WARN | CHASE_NONEXISTENT, &resolved, NULL);
if (r >= 0 &&
lp->root_dir &&
path_equal_ptr(path_startswith(resolved, lp->root_dir), "dev/null"))
/* When looking under root_dir, we can't expect /dev/ to be mounted,
* so let's see if the path is a (possibly dangling) symlink to /dev/null. */
/* This is a symlink, let's read and verify it. */
r = unit_file_resolve_symlink(lp->root_dir, lp->search_path,
NULL, AT_FDCWD, path,
true, &info->symlink_target);
if (r < 0)
return r;
r = null_or_empty_path_with_root(info->symlink_target, lp->root_dir);
if (r < 0 && r != -ENOENT)
return log_debug_errno(r, "Failed to stat %s: %m", info->symlink_target);
if (r > 0)
info->type = UNIT_FILE_TYPE_MASKED;
else if (r > 0 && null_or_empty_path(resolved) > 0)
info->type = UNIT_FILE_TYPE_MASKED;
else {
_cleanup_free_ char *target = NULL;
const char *bn;
UnitType a, b;
/* This is a symlink, let's read it. We read the link again, because last time
* we followed the link until resolution, and here we need to do one step. */
r = readlink_malloc(path, &target);
if (r < 0)
return r;
bn = basename(target);
if (unit_name_is_valid(info->name, UNIT_NAME_PLAIN)) {
if (!unit_name_is_valid(bn, UNIT_NAME_PLAIN))
return -EINVAL;
} else if (unit_name_is_valid(info->name, UNIT_NAME_INSTANCE)) {
if (!unit_name_is_valid(bn, UNIT_NAME_INSTANCE|UNIT_NAME_TEMPLATE))
return -EINVAL;
} else if (unit_name_is_valid(info->name, UNIT_NAME_TEMPLATE)) {
if (!unit_name_is_valid(bn, UNIT_NAME_TEMPLATE))
return -EINVAL;
} else
return -EINVAL;
/* Enforce that the symlink destination does not
* change the unit file type. */
a = unit_name_to_type(info->name);
b = unit_name_to_type(bn);
if (a < 0 || b < 0 || a != b)
return -EINVAL;
if (path_is_absolute(target))
/* This is an absolute path, prefix the root so that we always deal with fully qualified paths */
info->symlink_target = path_join(lp->root_dir, target);
else
/* This is a relative path, take it relative to the dir the symlink is located in. */
info->symlink_target = file_in_same_dir(path, target);
if (!info->symlink_target)
return -ENOMEM;
else
info->type = UNIT_FILE_TYPE_SYMLINK;
}
return 0;
}