path-util: Fix path_is_mount_point for files

Commits 27cc6f166 and f25afeb broke path_is_mount_point() for files (such as
/etc/machine-id → /run/machine-id bind mounts) as with the factorization of
fd_is_mount_point() we lost the parent directory. We cannot determine that from
an fd only as openat(fd, "..") only works for directory fds.

Change fd_is_mount_point() to behave like openat(): It now takes a file
descriptor of the containing directory, a file name in it, and flags (which can
be 0 or AT_SYMLINK_FOLLOW). Unlike name_to_handle_at() or openat(), fstatat()
only accepts the inverse flag AT_SYMLINK_NOFOLLOW and complains with EINVAL
about AT_SYMLINK_FOLLOW; so we need to transform the flags for that fallback.

Adjust rm_rf_children() accordingly (only other caller of fd_is_mount_point()
aside from path_is_mount_point()).

Add test cases for files, links, and file bind mounts (the latter will only
work when running as root). Split out a new test_path_is_mount_point() test
case function as it got significantly larger now.

1 files changed, 63 insertions, 13 deletions

diff --git a/src/test/test-path-util.c b/src/test/test-path-util.c
index 09f0f2f89e..80782ff902 100644
--- a/src/test/test-path-util.c
+++ b/src/test/test-path-util.c
@@ -21,6 +21,7 @@
 
 #include <stdio.h>
 #include <unistd.h>
+#include <sys/mount.h>
 
 #include "path-util.h"
 #include "util.h"
@@ -88,21 +89,9 @@ static void test_path(void) {
         test_parent("/aa///file...", "/aa///");
         test_parent("file.../", NULL);
 
-        assert_se(path_is_mount_point("/", true) > 0);
-        assert_se(path_is_mount_point("/", false) > 0);
-
         fd = open("/", O_RDONLY|O_CLOEXEC|O_DIRECTORY|O_NOCTTY);
         assert_se(fd >= 0);
-        assert_se(fd_is_mount_point(fd) > 0);
-
-        assert_se(path_is_mount_point("/proc", true) > 0);
-        assert_se(path_is_mount_point("/proc", false) > 0);
-
-        assert_se(path_is_mount_point("/proc/1", true) == 0);
-        assert_se(path_is_mount_point("/proc/1", false) == 0);
-
-        assert_se(path_is_mount_point("/sys", true) > 0);
-        assert_se(path_is_mount_point("/sys", false) > 0);
+        assert_se(fd_is_mount_point(fd, "/", 0) > 0);
 
         {
                 char p1[] = "aaa/bbb////ccc";
@@ -322,6 +311,66 @@ static void test_prefix_root(void) {
         test_prefix_root_one("/foo///", "//bar", "/foo/bar");
 }
 
+static void test_path_is_mount_point(void) {
+        int fd, rt, rf, rlt, rlf;
+        char tmp_dir[] = "/tmp/test-path-is-mount-point-XXXXXX";
+        _cleanup_free_ char *file1 = NULL, *file2 = NULL, *link1 = NULL, *link2 = NULL;
+
+        assert_se(path_is_mount_point("/", true) > 0);
+        assert_se(path_is_mount_point("/", false) > 0);
+
+        assert_se(path_is_mount_point("/proc", true) > 0);
+        assert_se(path_is_mount_point("/proc", false) > 0);
+
+        assert_se(path_is_mount_point("/proc/1", true) == 0);
+        assert_se(path_is_mount_point("/proc/1", false) == 0);
+
+        assert_se(path_is_mount_point("/sys", true) > 0);
+        assert_se(path_is_mount_point("/sys", false) > 0);
+
+        /* file mountpoints */
+        assert_se(mkdtemp(tmp_dir) != NULL);
+        file1 = path_join(NULL, tmp_dir, "file1");
+        assert_se(file1);
+        file2 = path_join(NULL, tmp_dir, "file2");
+        assert_se(file2);
+        fd = open(file1, O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0664);
+        assert_se(fd > 0);
+        close(fd);
+        fd = open(file2, O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, 0664);
+        assert_se(fd > 0);
+        close(fd);
+        link1 = path_join(NULL, tmp_dir, "link1");
+        assert_se(link1);
+        assert_se(symlink("file1", link1) == 0);
+        link2 = path_join(NULL, tmp_dir, "link2");
+        assert_se(link1);
+        assert_se(symlink("file2", link2) == 0);
+
+        assert_se(path_is_mount_point(file1, true) == 0);
+        assert_se(path_is_mount_point(file1, false) == 0);
+        assert_se(path_is_mount_point(link1, true) == 0);
+        assert_se(path_is_mount_point(link1, false) == 0);
+
+        /* this test will only work as root */
+        if (mount(file1, file2, NULL, MS_BIND, NULL) >= 0) {
+                rf = path_is_mount_point(file2, false);
+                rt = path_is_mount_point(file2, true);
+                rlf = path_is_mount_point(link2, false);
+                rlt = path_is_mount_point(link2, true);
+
+                assert_se(umount(file2) == 0);
+
+                assert_se(rf == 1);
+                assert_se(rt == 1);
+                assert_se(rlf == 0);
+                assert_se(rlt == 1);
+        } else
+                printf("Skipping bind mount file test: %m\n");
+
+        assert_se(rm_rf(tmp_dir, REMOVE_ROOT|REMOVE_PHYSICAL) == 0);
+}
+
 int main(int argc, char **argv) {
         test_path();
         test_find_binary(argv[0], true);
@@ -333,6 +382,7 @@ int main(int argc, char **argv) {
         test_strv_resolve();
         test_path_startswith();
         test_prefix_root();
+        test_path_is_mount_point();
 
         return 0;
 }