Merge pull request #14400 from keszybz/alias-check

Alias check rework

src/shared/install.c

@@ -1703,6 +1703,82 @@ static int install_info_discover_and_check(
         return install_info_may_process(ret ? *ret : NULL, paths, changes, n_changes);
 }
 
+int unit_file_verify_alias(const UnitFileInstallInfo *i, const char *dst, char **ret_dst) {
+        _cleanup_free_ char *dst_updated = NULL;
+        int r;
+
+        /* Verify that dst is a valid either a valid alias or a valid .wants/.requires symlink for the target
+         * unit *i. Return negative on error or if not compatible, zero on success.
+         *
+         * ret_dst is set in cases where "instance propagation" happens, i.e. when the instance part is
+         * inserted into dst. It is not normally set, even on success, so that the caller can easily
+         * distinguish the case where instance propagation occured.
+         */
+
+        const char *path_alias = strrchr(dst, '/');
+        if (path_alias) {
+                /* This branch covers legacy Alias= function of creating .wants and .requires symlinks. */
+                _cleanup_free_ char *dir = NULL;
+                char *p;
+
+                path_alias ++; /* skip over slash */
+
+                dir = dirname_malloc(dst);
+                if (!dir)
+                        return log_oom();
+
+                p = endswith(dir, ".wants");
+                if (!p)
+                        p = endswith(dir, ".requires");
+                if (!p)
+                        return log_warning_errno(SYNTHETIC_ERRNO(EXDEV),
+                                                 "Invalid path \"%s\" in alias.", dir);
+                *p = '\0'; /* dir should now be a unit name */
+
+                r = unit_name_classify(dir);
+                if (r < 0)
+                        return log_warning_errno(SYNTHETIC_ERRNO(EXDEV),
+                                                 "Invalid unit name component \"%s\" in alias.", dir);
+
+                const bool instance_propagation = r == UNIT_NAME_TEMPLATE;
+
+                /* That's the name we want to use for verification. */
+                r = unit_symlink_name_compatible(path_alias, i->name, instance_propagation);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to verify alias validity: %m");
+                if (r == 0)
+                        return log_warning_errno(SYNTHETIC_ERRNO(EXDEV),
+                                                 "Invalid unit %s symlink %s.",
+                                                 i->name, dst);
+
+        } else {
+                /* If the symlink target has an instance set and the symlink source doesn't, we "propagate
+                 * the instance", i.e. instantiate the symlink source with the target instance. */
+                if (unit_name_is_valid(dst, UNIT_NAME_TEMPLATE)) {
+                        _cleanup_free_ char *inst = NULL;
+
+                        r = unit_name_to_instance(i->name, &inst);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to extract instance name from %s: %m", i->name);
+
+                        if (r == UNIT_NAME_INSTANCE) {
+                                r = unit_name_replace_instance(dst, inst, &dst_updated);
+                                if (r < 0)
+                                        return log_error_errno(r, "Failed to build unit name from %s+%s: %m",
+                                                               dst, inst);
+                        }
+                }
+
+                r = unit_validate_alias_symlink_and_warn(dst_updated ?: dst, i->name);
+                if (r < 0)
+                        return r;
+
+        }
+
+        *ret_dst = TAKE_PTR(dst_updated);
+        return 0;
+}
+
 static int install_info_symlink_alias(
                 UnitFileInstallInfo *i,
                 const LookupPaths *paths,
@@ -1719,13 +1795,17 @@ static int install_info_symlink_alias(
         assert(config_path);
 
         STRV_FOREACH(s, i->aliases) {
-                _cleanup_free_ char *alias_path = NULL, *dst = NULL;
+                _cleanup_free_ char *alias_path = NULL, *dst = NULL, *dst_updated = NULL;
 
                 q = install_full_printf(i, *s, &dst);
                 if (q < 0)
                         return q;
 
-                alias_path = path_make_absolute(dst, config_path);
+                q = unit_file_verify_alias(i, dst, &dst_updated);
+                if (q < 0)
+                        continue;
+
+                alias_path = path_make_absolute(dst_updated ?: dst, config_path);
                 if (!alias_path)
                         return -ENOMEM;
 

src/shared/install.h

@@ -187,6 +187,8 @@ int unit_file_changes_add(UnitFileChange **changes, size_t *n_changes, UnitFileC
 void unit_file_changes_free(UnitFileChange *changes, size_t n_changes);
 void unit_file_dump_changes(int r, const char *verb, const UnitFileChange *changes, size_t n_changes, bool quiet);
 
+int unit_file_verify_alias(const UnitFileInstallInfo *i, const char *dst, char **ret_dst);
+
 int unit_file_query_preset(UnitFileScope scope, const char *root_dir, const char *name);
 
 const char *unit_file_state_to_string(UnitFileState s) _const_;

src/shared/unit-file.c

@@ -31,6 +31,41 @@ bool unit_type_may_template(UnitType type) {
                       UNIT_PATH);
 }
 
+int unit_symlink_name_compatible(const char *symlink, const char *target, bool instance_propagation) {
+        _cleanup_free_ char *template = NULL;
+        int r, un_type1, un_type2;
+
+        un_type1 = unit_name_classify(symlink);
+
+        /* The straightforward case: the symlink name matches the target and we have a valid unit */
+        if (streq(symlink, target) &&
+            (un_type1 & (UNIT_NAME_PLAIN | UNIT_NAME_INSTANCE)))
+                return 1;
+
+        r = unit_name_template(symlink, &template);
+        if (r == -EINVAL)
+                return 0; /* Not a template */
+        if (r < 0)
+                return r;
+
+        un_type2 = unit_name_classify(target);
+
+        /* An instance name points to a target that is just the template name */
+        if (un_type1 == UNIT_NAME_INSTANCE &&
+            un_type2 == UNIT_NAME_TEMPLATE &&
+            streq(template, target))
+                return 1;
+
+        /* foo@.target.requires/bar@.service: instance will be propagated */
+        if (instance_propagation &&
+            un_type1 == UNIT_NAME_TEMPLATE &&
+            un_type2 == UNIT_NAME_TEMPLATE &&
+            streq(template, target))
+                return 1;
+
+        return 0;
+}
+
 int unit_validate_alias_symlink_and_warn(const char *filename, const char *target) {
         const char *src, *dst;
         _cleanup_free_ char *src_instance = NULL, *dst_instance = NULL;

src/shared/unit-file.h

@@ -39,6 +39,7 @@ enum UnitFileScope {
 bool unit_type_may_alias(UnitType type) _const_;
 bool unit_type_may_template(UnitType type) _const_;
 
+int unit_symlink_name_compatible(const char *symlink, const char *target, bool instance_propagation);
 int unit_validate_alias_symlink_and_warn(const char *filename, const char *target);
 
 int unit_file_build_name_map(