Merge pull request #15955 from anitazha/nullorempty

core: check null_or_empty_path for masked units instead of /dev/null

3 files changed, 41 insertions, 10 deletions

diff --git a/src/core/unit.c b/src/core/unit.c
index edc96537cb..2c09def06f 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -5955,7 +5955,7 @@ const char *unit_label_path(const Unit *u) {
                 return NULL;
 
         /* If a unit is masked, then don't read the SELinux label of /dev/null, as that really makes no sense */
-        if (path_equal(p, "/dev/null"))
+        if (null_or_empty_path(p) > 0)
                 return NULL;
 
         return p;
diff --git a/src/shared/install.c b/src/shared/install.c
index bb2eff7387..fb5e166ff0 100644
--- a/src/shared/install.c
+++ b/src/shared/install.c
@@ -1236,8 +1236,7 @@ static int unit_file_load(
                                                "%s: unit type %s cannot be templated, ignoring.", path, unit_type_to_string(type));
 
                 if (!(flags & SEARCH_LOAD)) {
-                        r = lstat(path, &st);
-                        if (r < 0)
+                        if (lstat(path, &st) < 0)
                                 return -errno;
 
                         if (null_or_empty(&st))
@@ -1324,26 +1323,40 @@ static int unit_file_load_or_readlink(
                 const char *path,
                 const char *root_dir,
                 SearchFlags flags) {
-
-        _cleanup_free_ char *target = NULL;
+        _cleanup_free_ char *resolved = NULL;
+        struct stat st;
         int r;
 
         r = unit_file_load(c, info, path, root_dir, flags);
         if (r != -ELOOP || (flags & SEARCH_DROPIN))
                 return r;
 
-        /* This is a symlink, let's read it. */
+        r = chase_symlinks(path, root_dir, CHASE_WARN | CHASE_NONEXISTENT, &resolved, NULL);
+        if (r >= 0 &&
+            root_dir &&
+            path_equal_ptr(path_startswith(resolved, 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. */
+                info->type = UNIT_FILE_TYPE_MASKED;
 
-        r = readlink_malloc(path, &target);
-        if (r < 0)
-                return r;
+        else if (r > 0 &&
+                 stat(resolved, &st) >= 0 &&
+                 null_or_empty(&st))
 
-        if (path_equal(target, "/dev/null"))
                 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)) {
diff --git a/src/test/test-install-root.c b/src/test/test-install-root.c
index 515f14b8ca..f309160889 100644
--- a/src/test/test-install-root.c
+++ b/src/test/test-install-root.c
@@ -4,6 +4,7 @@
 
 #include "alloc-util.h"
 #include "fileio.h"
+#include "fs-util.h"
 #include "install.h"
 #include "mkdir.h"
 #include "rm-rf.h"
@@ -23,6 +24,7 @@ static void test_basic_mask_and_enable(const char *root) {
         assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "b.service", NULL) == -ENOENT);
         assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "c.service", NULL) == -ENOENT);
         assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "d.service", NULL) == -ENOENT);
+        assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "e.service", NULL) == -ENOENT);
 
         p = strjoina(root, "/usr/lib/systemd/system/a.service");
         assert_se(write_string_file(p,
@@ -150,6 +152,22 @@ static void test_basic_mask_and_enable(const char *root) {
         assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "b.service", &state) >= 0 && state == UNIT_FILE_ALIAS);
         assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "c.service", &state) >= 0 && state == UNIT_FILE_ALIAS);
         assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "d.service", &state) >= 0 && state == UNIT_FILE_ALIAS);
+
+        /* Test masking with relative symlinks */
+
+        p = strjoina(root, "/usr/lib/systemd/system/e.service");
+        assert_se(symlink("../../../../../../dev/null", p) >= 0);
+
+        assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "e.service", NULL) >= 0);
+        assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "e.service", &state) >= 0 && state == UNIT_FILE_MASKED);
+
+        assert_se(unlink(p) == 0);
+        assert_se(symlink("/usr/../dev/null", p) >= 0);
+
+        assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "e.service", NULL) >= 0);
+        assert_se(unit_file_get_state(UNIT_FILE_SYSTEM, root, "e.service", &state) >= 0 && state == UNIT_FILE_MASKED);
+
+        assert_se(unlink(p) == 0);
 }
 
 static void test_linked_units(const char *root) {