tmpfiles: add conditionalized execute bit (X) support

According to setfacl(1), "the character X stands for
the execute permission if the file is a directory
or already has execute permission for some user."

After this commit, parse_acl() would return 3 acl
objects. The newly-added acl_exec object contains
entries that are subject to conditionalized execute
bit mangling. In tmpfiles, we would iterate the acl_exec
object, check the permission of the target files,
and remove the execute bit if necessary.

Here's an example entry:
A /tmp/test - - - - u:test:rwX

Closes #25114

src/shared/acl-util.c

@@ -209,14 +209,20 @@ int acl_search_groups(const char *path, char ***ret_groups) {
         return ret;
 }
 
-int parse_acl(const char *text, acl_t *ret_acl_access, acl_t *ret_acl_default, bool want_mask) {
-        _cleanup_free_ char **a = NULL, **d = NULL; /* strings are not freed */
-        _cleanup_strv_free_ char **split = NULL;
-        int r = -EINVAL;
-        _cleanup_(acl_freep) acl_t a_acl = NULL, d_acl = NULL;
+int parse_acl(
+                const char *text,
+                acl_t *ret_acl_access,
+                acl_t *ret_acl_access_exec, /* extra rules to apply to inodes subject to uppercase X handling */
+                acl_t *ret_acl_default,
+                bool want_mask) {
+
+        _cleanup_strv_free_ char **a = NULL, **e = NULL, **d = NULL, **split = NULL;
+        _cleanup_(acl_freep) acl_t a_acl = NULL, e_acl = NULL, d_acl = NULL;
+        int r;
 
         assert(text);
         assert(ret_acl_access);
+        assert(ret_acl_access_exec);
         assert(ret_acl_default);
 
         split = strv_split(text, ",");
@@ -224,13 +230,38 @@ int parse_acl(const char *text, acl_t *ret_acl_access, acl_t *ret_acl_default, b
                 return -ENOMEM;
 
         STRV_FOREACH(entry, split) {
-                char *p;
+                _cleanup_strv_free_ char **entry_split = NULL;
+                _cleanup_free_ char *entry_join = NULL;
+                int n;
 
-                p = STARTSWITH_SET(*entry, "default:", "d:");
-                if (p)
-                        r = strv_push(&d, p);
-                else
-                        r = strv_push(&a, *entry);
+                n = strv_split_full(&entry_split, *entry, ":", EXTRACT_DONT_COALESCE_SEPARATORS|EXTRACT_RETAIN_ESCAPE);
+                if (n < 0)
+                        return n;
+
+                if (n < 3 || n > 4)
+                        return -EINVAL;
+
+                string_replace_char(entry_split[n-1], 'X', 'x');
+
+                if (n == 4) {
+                        if (!STR_IN_SET(entry_split[0], "default", "d"))
+                                return -EINVAL;
+
+                        entry_join = strv_join(entry_split + 1, ":");
+                        if (!entry_join)
+                                return -ENOMEM;
+
+                        r = strv_consume(&d, TAKE_PTR(entry_join));
+                } else { /* n == 3 */
+                        entry_join = strv_join(entry_split, ":");
+                        if (!entry_join)
+                                return -ENOMEM;
+
+                        if (!streq(*entry, entry_join))
+                                r = strv_consume(&e, TAKE_PTR(entry_join));
+                        else
+                                r = strv_consume(&a, TAKE_PTR(entry_join));
+                }
                 if (r < 0)
                         return r;
         }
@@ -253,6 +284,20 @@ int parse_acl(const char *text, acl_t *ret_acl_access, acl_t *ret_acl_default, b
                 }
         }
 
+        if (!strv_isempty(e)) {
+                _cleanup_free_ char *join = NULL;
+
+                join = strv_join(e, ",");
+                if (!join)
+                        return -ENOMEM;
+
+                e_acl = acl_from_text(join);
+                if (!e_acl)
+                        return -errno;
+
+                /* The mask must be calculated after deciding whether the execute bit should be set. */
+        }
+
         if (!strv_isempty(d)) {
                 _cleanup_free_ char *join = NULL;
 
@@ -272,6 +317,7 @@ int parse_acl(const char *text, acl_t *ret_acl_access, acl_t *ret_acl_default, b
         }
 
         *ret_acl_access = TAKE_PTR(a_acl);
+        *ret_acl_access_exec = TAKE_PTR(e_acl);
         *ret_acl_default = TAKE_PTR(d_acl);
 
         return 0;

src/shared/acl-util.h

@@ -15,7 +15,12 @@ int acl_find_uid(acl_t acl, uid_t uid, acl_entry_t *entry);
 int calc_acl_mask_if_needed(acl_t *acl_p);
 int add_base_acls_if_needed(acl_t *acl_p, const char *path);
 int acl_search_groups(const char* path, char ***ret_groups);
-int parse_acl(const char *text, acl_t *ret_acl_access, acl_t *ret_acl_default, bool want_mask);
+int parse_acl(
+                const char *text,
+                acl_t *ret_acl_access,
+                acl_t *ret_acl_access_exec,
+                acl_t *ret_acl_default,
+                bool want_mask);
 int acls_for_file(const char *path, acl_type_t type, acl_t new, acl_t *ret);
 int fd_add_uid_acl_permission(int fd, uid_t uid, unsigned mask);