Merge pull request #18579 from keszybz/fix-fragment-id-crash

Fix fragment id crash

src/basic/unit-file.c

@@ -354,10 +354,16 @@ int unit_file_build_name_map(
 
                                 /* 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 destination directly.
+                                 * Let's just store the link source directly.
                                  * If not, let's verify that it's a good symlink. */
                                 char *tail = path_startswith_strv(simplified, lp->search_path);
-                                if (tail) {
+                                if (!tail) {
+                                        log_debug("%s: linked unit file: %s → %s",
+                                                  __func__, filename, simplified);
+
+                                        dst = filename;
+                                } else {
+
                                         bool self_alias;
 
                                         dst = basename(simplified);
@@ -380,10 +386,6 @@ int unit_file_build_name_map(
                                         }
 
                                         log_debug("%s: alias: %s/%s → %s", __func__, *dir, de->d_name, dst);
-                                } else {
-                                        dst  = simplified;
-
-                                        log_debug("%s: linked unit file: %s/%s → %s", __func__, *dir, de->d_name, dst);
                                 }
 
                         } else {

src/core/load-fragment.c

@@ -5536,10 +5536,11 @@ int unit_load_fragment(Unit *u) {
                 }
         }
 
-        /* We do the merge dance here because for some unit types, the unit might have aliases which are not
+        /* Call merge_by_names with the name derived from the fragment path as the preferred name.
+         *
+         * We do the merge dance here because for some unit types, the unit might have aliases which are not
          * declared in the file system. In particular, this is true (and frequent) for device and swap units.
          */
-        Unit *merged;
         const char *id = u->id;
         _cleanup_free_ char *free_id = NULL;
 
@@ -5556,7 +5557,7 @@ int unit_load_fragment(Unit *u) {
                 }
         }
 
-        merged = u;
+        Unit *merged = u;
         r = merge_by_names(&merged, names, id);
         if (r < 0)
                 return r;

test/units/testsuite-15.sh

@@ -124,6 +124,32 @@ EOF
     clear_services test15-a test15-b test15-c
 }
 
+test_linked_units () {
+    echo "Testing linked units..."
+    echo "*** test linked unit (same basename)"
+
+    create_service test15-a
+    mv /etc/systemd/system/test15-a.service /
+    ln -s /test15-a.service /etc/systemd/system/
+    ln -s test15-a.service /etc/systemd/system/test15-b.service
+
+    check_ok test15-a Names test15-a.service
+    check_ok test15-a Names test15-b.service
+
+    echo "*** test linked unit (cross basename)"
+
+    mv /test15-a.service /test15-a@.scope
+    ln -fs /test15-a@.scope /etc/systemd/system/test15-a.service
+    systemctl daemon-reload
+
+    check_ok test15-a Names test15-a.service
+    check_ok test15-a Names test15-b.service
+    check_ko test15-a Names test15-b@
+
+    rm /test15-a@.scope
+    clear_services test15-a test15-b
+}
+
 test_hierarchical_dropins () {
     echo "Testing hierarchical dropins..."
     echo "*** test service.d/ top level drop-in"
@@ -465,6 +491,7 @@ test_invalid_dropins () {
 }
 
 test_basic_dropins
+test_linked_units
 test_hierarchical_dropins
 test_template_dropins
 test_alias_dropins