selftests: add tests for using detached mount with overlayfs

Test that it is possible to use detached mounts as overlayfs layers.

Link: https://lore.kernel.org/r/20250123-erstbesteigung-angeeignet-1d30e64b7df2@brauner
Signed-off-by: Christian Brauner <brauner@kernel.org>

2 files changed, 147 insertions, 0 deletions

diff --git a/tools/testing/selftests/filesystems/overlayfs/set_layers_via_fds.c b/tools/testing/selftests/filesystems/overlayfs/set_layers_via_fds.c
index e693e4102d22..e65d95d97846 100644
--- a/tools/testing/selftests/filesystems/overlayfs/set_layers_via_fds.c
+++ b/tools/testing/selftests/filesystems/overlayfs/set_layers_via_fds.c
@@ -20,12 +20,16 @@ FIXTURE(set_layers_via_fds) {
 FIXTURE_SETUP(set_layers_via_fds)
 {
 	ASSERT_EQ(mkdir("/set_layers_via_fds", 0755), 0);
+	ASSERT_EQ(mkdir("/set_layers_via_fds_tmpfs", 0755), 0);
 }
 
 FIXTURE_TEARDOWN(set_layers_via_fds)
 {
 	umount2("/set_layers_via_fds", 0);
 	ASSERT_EQ(rmdir("/set_layers_via_fds"), 0);
+
+	umount2("/set_layers_via_fds_tmpfs", 0);
+	ASSERT_EQ(rmdir("/set_layers_via_fds_tmpfs"), 0);
 }
 
 TEST_F(set_layers_via_fds, set_layers_via_fds)
@@ -279,4 +283,130 @@ TEST_F(set_layers_via_fds, set_500_layers_via_opath_fds)
 	ASSERT_EQ(close(fd_overlay), 0);
 }
 
+TEST_F(set_layers_via_fds, set_layers_via_detached_mount_fds)
+{
+	int fd_context, fd_tmpfs, fd_overlay, fd_tmp;
+	int layer_fds[] = { [0 ... 8] = -EBADF };
+	bool layers_found[] = { [0 ... 8] =  false };
+	size_t len = 0;
+	char *line = NULL;
+	FILE *f_mountinfo;
+
+	ASSERT_EQ(unshare(CLONE_NEWNS), 0);
+	ASSERT_EQ(sys_mount(NULL, "/", NULL, MS_SLAVE | MS_REC, NULL), 0);
+
+	fd_context = sys_fsopen("tmpfs", 0);
+	ASSERT_GE(fd_context, 0);
+
+	ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_CMD_CREATE, NULL, NULL, 0), 0);
+	fd_tmpfs = sys_fsmount(fd_context, 0, 0);
+	ASSERT_GE(fd_tmpfs, 0);
+	ASSERT_EQ(close(fd_context), 0);
+
+	ASSERT_EQ(mkdirat(fd_tmpfs, "u", 0755), 0);
+	ASSERT_EQ(mkdirat(fd_tmpfs, "u/upper", 0755), 0);
+	ASSERT_EQ(mkdirat(fd_tmpfs, "u/work", 0755), 0);
+	ASSERT_EQ(mkdirat(fd_tmpfs, "l1", 0755), 0);
+	ASSERT_EQ(mkdirat(fd_tmpfs, "l2", 0755), 0);
+	ASSERT_EQ(mkdirat(fd_tmpfs, "l3", 0755), 0);
+	ASSERT_EQ(mkdirat(fd_tmpfs, "l4", 0755), 0);
+	ASSERT_EQ(mkdirat(fd_tmpfs, "d1", 0755), 0);
+	ASSERT_EQ(mkdirat(fd_tmpfs, "d2", 0755), 0);
+	ASSERT_EQ(mkdirat(fd_tmpfs, "d3", 0755), 0);
+
+	ASSERT_EQ(sys_move_mount(fd_tmpfs, "", -EBADF, "/set_layers_via_fds_tmpfs", MOVE_MOUNT_F_EMPTY_PATH), 0);
+
+	fd_tmp = open_tree(fd_tmpfs, "u", OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC);
+	ASSERT_GE(fd_tmp, 0);
+
+	layer_fds[0] = openat(fd_tmp, "upper", O_CLOEXEC | O_DIRECTORY | O_PATH);
+	ASSERT_GE(layer_fds[0], 0);
+
+	layer_fds[1] = openat(fd_tmp, "work", O_CLOEXEC | O_DIRECTORY | O_PATH);
+	ASSERT_GE(layer_fds[1], 0);
+
+	layer_fds[2] = open_tree(fd_tmpfs, "l1", OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC);
+	ASSERT_GE(layer_fds[2], 0);
+
+	layer_fds[3] = open_tree(fd_tmpfs, "l2", OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC);
+	ASSERT_GE(layer_fds[3], 0);
+
+	layer_fds[4] = open_tree(fd_tmpfs, "l3", OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC);
+	ASSERT_GE(layer_fds[4], 0);
+
+	layer_fds[5] = open_tree(fd_tmpfs, "l4", OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC);
+	ASSERT_GE(layer_fds[5], 0);
+
+	layer_fds[6] = open_tree(fd_tmpfs, "d1", OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC);
+	ASSERT_GE(layer_fds[6], 0);
+
+	layer_fds[7] = open_tree(fd_tmpfs, "d2", OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC);
+	ASSERT_GE(layer_fds[7], 0);
+
+	layer_fds[8] = open_tree(fd_tmpfs, "d3", OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC);
+	ASSERT_GE(layer_fds[8], 0);
+
+	ASSERT_EQ(close(fd_tmpfs), 0);
+
+	fd_context = sys_fsopen("overlay", 0);
+	ASSERT_GE(fd_context, 0);
+
+	ASSERT_NE(sys_fsconfig(fd_context, FSCONFIG_SET_FD, "lowerdir", NULL, layer_fds[2]), 0);
+
+	ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_SET_FD, "upperdir",  NULL, layer_fds[0]), 0);
+	ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_SET_FD, "workdir",   NULL, layer_fds[1]), 0);
+	ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_SET_FD, "lowerdir+", NULL, layer_fds[2]), 0);
+	ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_SET_FD, "lowerdir+", NULL, layer_fds[3]), 0);
+	ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_SET_FD, "lowerdir+", NULL, layer_fds[4]), 0);
+	ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_SET_FD, "lowerdir+", NULL, layer_fds[5]), 0);
+	ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_SET_FD, "datadir+",  NULL, layer_fds[6]), 0);
+	ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_SET_FD, "datadir+",  NULL, layer_fds[7]), 0);
+	ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_SET_FD, "datadir+",  NULL, layer_fds[8]), 0);
+
+	ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_SET_STRING, "metacopy", "on", 0), 0);
+
+	ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_CMD_CREATE, NULL, NULL, 0), 0);
+
+	fd_overlay = sys_fsmount(fd_context, 0, 0);
+	ASSERT_GE(fd_overlay, 0);
+
+	ASSERT_EQ(sys_move_mount(fd_overlay, "", -EBADF, "/set_layers_via_fds", MOVE_MOUNT_F_EMPTY_PATH), 0);
+
+	f_mountinfo = fopen("/proc/self/mountinfo", "r");
+	ASSERT_NE(f_mountinfo, NULL);
+
+	while (getline(&line, &len, f_mountinfo) != -1) {
+		char *haystack = line;
+
+		if (strstr(haystack, "workdir=/tmp/w"))
+			layers_found[0] = true;
+		if (strstr(haystack, "upperdir=/tmp/u"))
+			layers_found[1] = true;
+		if (strstr(haystack, "lowerdir+=/tmp/l1"))
+			layers_found[2] = true;
+		if (strstr(haystack, "lowerdir+=/tmp/l2"))
+			layers_found[3] = true;
+		if (strstr(haystack, "lowerdir+=/tmp/l3"))
+			layers_found[4] = true;
+		if (strstr(haystack, "lowerdir+=/tmp/l4"))
+			layers_found[5] = true;
+		if (strstr(haystack, "datadir+=/tmp/d1"))
+			layers_found[6] = true;
+		if (strstr(haystack, "datadir+=/tmp/d2"))
+			layers_found[7] = true;
+		if (strstr(haystack, "datadir+=/tmp/d3"))
+			layers_found[8] = true;
+	}
+	free(line);
+
+	for (int i = 0; i < ARRAY_SIZE(layer_fds); i++) {
+		ASSERT_EQ(layers_found[i], true);
+		ASSERT_EQ(close(layer_fds[i]), 0);
+	}
+
+	ASSERT_EQ(close(fd_context), 0);
+	ASSERT_EQ(close(fd_overlay), 0);
+	ASSERT_EQ(fclose(f_mountinfo), 0);
+}
+
 TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/filesystems/overlayfs/wrappers.h b/tools/testing/selftests/filesystems/overlayfs/wrappers.h
index 071b95fd2ac0..c38bc48e0cfa 100644
--- a/tools/testing/selftests/filesystems/overlayfs/wrappers.h
+++ b/tools/testing/selftests/filesystems/overlayfs/wrappers.h
@@ -44,4 +44,21 @@ static inline int sys_move_mount(int from_dfd, const char *from_pathname,
 		       to_pathname, flags);
 }
 
+#ifndef OPEN_TREE_CLONE
+#define OPEN_TREE_CLONE 1
+#endif
+
+#ifndef OPEN_TREE_CLOEXEC
+#define OPEN_TREE_CLOEXEC O_CLOEXEC
+#endif
+
+#ifndef AT_RECURSIVE
+#define AT_RECURSIVE 0x8000
+#endif
+
+static inline int sys_open_tree(int dfd, const char *filename, unsigned int flags)
+{
+	return syscall(__NR_open_tree, dfd, filename, flags);
+}
+
 #endif