FAILED: patch "[PATCH] landlock: Require LANDLOCK_ACCESS_FS_MAKE_REG for whiteout" failed to apply to 6.6-stable tree

index 272f047df438..27ae3f39cafb 100644
@@ -351,6 +351,7 @@ struct landlock_net_port_attr {
  *   device.
  * - %LANDLOCK_ACCESS_FS_MAKE_DIR: Create (or rename) a directory.
  * - %LANDLOCK_ACCESS_FS_MAKE_REG: Create (or rename or link) a regular file.
+ *   This also guards the creation of whiteout objects as used in OverlayFS.
  * - %LANDLOCK_ACCESS_FS_MAKE_SOCK: Create (or rename or link) a UNIX domain
  *   socket.
  * - %LANDLOCK_ACCESS_FS_MAKE_FIFO: Create (or rename or link) a named pipe.

index 3f099555f059..315ea7e0fe50 100644
@@ -22,3 +22,26 @@
  * from their original mount points.
  */
 LANDLOCK_ERRATUM(3)
+
+/**
+ * DOC: erratum_4
+ *
+ * Erratum 4: Creation of whiteout objects
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * This fix changes the access rights required for the creation of whiteout
+ * objects through :manpage:`mknod(2)`, :manpage:`renameat2(2)`, or
+ * :manpage:`link(2)`.  Creating whiteout objects is now guarded by
+ * ``LANDLOCK_ACCESS_FS_MAKE_REG`` instead of ``LANDLOCK_ACCESS_FS_MAKE_CHAR``.
+ *
+ * Whiteout objects are used in OverlayFS to mark the absence of a file in an
+ * upper file system.  Despite being created with ``S_IFCHR``, whiteout objects
+ * do not count as character devices.
+ *
+ * Impact:
+ *
+ * Sandboxed programs that create OverlayFS whiteouts (such as fuse-overlayfs)
+ * now require ``LANDLOCK_ACCESS_FS_MAKE_REG`` instead of
+ * ``LANDLOCK_ACCESS_FS_MAKE_CHAR``.
+ */
+LANDLOCK_ERRATUM(4)

109 lines not on this page · raw message

index f82a66361a1e..4dc38ef34cbd 100644
@@ -126,6 +126,7 @@ struct landlock_path_beneath_attr {
  *   device.
  * - %LANDLOCK_ACCESS_FS_MAKE_DIR: Create (or rename) a directory.
  * - %LANDLOCK_ACCESS_FS_MAKE_REG: Create (or rename or link) a regular file.
+ *   This also guards the creation of whiteout objects as used in OverlayFS.
  * - %LANDLOCK_ACCESS_FS_MAKE_SOCK: Create (or rename or link) a UNIX domain
  *   socket.
  * - %LANDLOCK_ACCESS_FS_MAKE_FIFO: Create (or rename or link) a named pipe.

index e8a2bff2e5b6..80930957e84d 100644
@@ -14,3 +14,26 @@
  * actions.
  */
 LANDLOCK_ERRATUM(3)
+
+/**
+ * DOC: erratum_4
+ *
+ * Erratum 4: Creation of whiteout objects
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * This fix changes the access rights required for the creation of whiteout
+ * objects through :manpage:`mknod(2)`, :manpage:`renameat2(2)`, or
+ * :manpage:`link(2)`.  Creating whiteout objects is now guarded by
+ * ``LANDLOCK_ACCESS_FS_MAKE_REG`` instead of ``LANDLOCK_ACCESS_FS_MAKE_CHAR``.
+ *
+ * Whiteout objects are used in OverlayFS to mark the absence of a file in an
+ * upper file system.  Despite being created with ``S_IFCHR``, whiteout objects
+ * do not count as character devices.
+ *
+ * Impact:
+ *
+ * Sandboxed programs that create OverlayFS whiteouts (such as fuse-overlayfs)
+ * now require ``LANDLOCK_ACCESS_FS_MAKE_REG`` instead of
+ * ``LANDLOCK_ACCESS_FS_MAKE_CHAR``.
+ */
+LANDLOCK_ERRATUM(4)

index 7145162f1e59..9c1cee4c4c3c 100644
@@ -15,6 +15,7 @@
 #include <linux/err.h>
 #include <linux/fs.h>
 #include <linux/init.h>
+#include <linux/kdev_t.h>
 #include <linux/kernel.h>
 #include <linux/limits.h>
 #include <linux/list.h>

@@ -671,7 +672,7 @@ static inline int current_check_access_path(const struct path *const path,
 	return check_access_path(dom, path, access_request);
 }
 
-static inline access_mask_t get_mode_access(const umode_t mode)
+static inline access_mask_t get_mode_access(const umode_t mode, const dev_t dev)
 {
 	switch (mode & S_IFMT) {
 	case S_IFLNK:

@@ -679,6 +680,9 @@ static inline access_mask_t get_mode_access(const umode_t mode)
 	case S_IFDIR:
 		return LANDLOCK_ACCESS_FS_MAKE_DIR;
 	case S_IFCHR:
+		/* Whiteout objects are guarded with MAKE_REG. */
+		if (dev == WHITEOUT_DEV)
+			return LANDLOCK_ACCESS_FS_MAKE_REG;
 		return LANDLOCK_ACCESS_FS_MAKE_CHAR;
 	case S_IFBLK:
 		return LANDLOCK_ACCESS_FS_MAKE_BLOCK;

@@ -695,6 +699,13 @@ static inline access_mask_t get_mode_access(const umode_t mode)
 	}
 }
 
+static inline access_mask_t get_dentry_access(const struct dentry *const dentry)
+{
+	const struct inode *const inode = d_backing_inode(dentry);
+
+	return get_mode_access(inode->i_mode, inode->i_rdev);
+}
+
 static inline access_mask_t maybe_remove(const struct dentry *const dentry)
 {
 	if (d_is_negative(dentry))

@@ -782,6 +793,7 @@ static bool collect_domain_accesses(
  * @new_dentry: Destination file or directory.
  * @removable: Sets to true if it is a rename operation.
  * @exchange: Sets to true if it is a rename operation with RENAME_EXCHANGE.
+ * @whiteout: Sets to true if it is a rename operation with RENAME_WHITEOUT.
  *
  * Because of its unprivileged constraints, Landlock relies on file hierarchies
  * (and not only inodes) to tie access rights to files.  Being able to link or

@@ -830,7 +842,8 @@ static bool collect_domain_accesses(
 static int current_check_refer_path(struct dentry *const old_dentry,
 				    const struct path *const new_dir,
 				    struct dentry *const new_dentry,
-				    const bool removable, const bool exchange)
+				    const bool removable, const bool exchange,
+				    const bool whiteout)
 {
 	const struct landlock_ruleset *const dom =
 		landlock_get_current_domain();

@@ -850,18 +863,25 @@ static int current_check_refer_path(struct dentry *const old_dentry,
 	if (exchange) {
 		if (unlikely(d_is_negative(new_dentry)))
 			return -ENOENT;
-		access_request_parent1 =
-			get_mode_access(d_backing_inode(new_dentry)->i_mode);
+		access_request_parent1 = get_dentry_access(new_dentry);
 	} else {
 		access_request_parent1 = 0;
 	}
-	access_request_parent2 =
-		get_mode_access(d_backing_inode(old_dentry)->i_mode);
+	access_request_parent2 = get_dentry_access(old_dentry);
 	if (removable) {
 		access_request_parent1 |= maybe_remove(old_dentry);
 		access_request_parent2 |= maybe_remove(new_dentry);
 	}
 
+	/*
+	 * In case of renameat2(2) with RENAME_WHITEOUT, a whiteout object is
+	 * created in the source location, so we require an additional access
+	 * right there.
+	 */
+	if (whiteout)
+		access_request_parent1 |=
+			get_mode_access(S_IFCHR | WHITEOUT_MODE, WHITEOUT_DEV);
+
 	/* The mount points are the same for old and new paths, cf. EXDEV. */
 	if (old_dentry->d_parent == new_dir->dentry) {
 		/*

@@ -1130,7 +1150,7 @@ static int hook_path_link(struct dentry *const old_dentry,
 			  struct dentry *const new_dentry)
 {
 	return current_check_refer_path(old_dentry, new_dir, new_dentry, false,
-					false);
+					false, false);
 }
 
 static int hook_path_rename(const struct path *const old_dir,

@@ -1141,7 +1161,8 @@ static int hook_path_rename(const struct path *const old_dir,
 {
 	/* old_dir refers to old_dentry->d_parent and new_dir->mnt */
 	return current_check_refer_path(old_dentry, new_dir, new_dentry, true,
-					!!(flags & RENAME_EXCHANGE));
+					!!(flags & RENAME_EXCHANGE),
+					!!(flags & RENAME_WHITEOUT));
 }
 
 static int hook_path_mkdir(const struct path *const dir,

@@ -1159,7 +1180,8 @@ static int hook_path_mknod(const struct path *const dir,
 
 	if (!dom)
 		return 0;
-	return check_access_path(dom, dir, get_mode_access(mode));
+	return check_access_path(dom, dir,
+				 get_mode_access(mode, new_decode_dev(dev)));
 }
 
 static int hook_path_symlink(const struct path *const dir,

index 9082ee10256a..f235552407af 100644
@@ -73,6 +73,8 @@ static const char file1_s3d1[] = TMP_DIR "/s3d1/f1";
 /* dir_s3d2 is a mount point. */
 static const char dir_s3d2[] = TMP_DIR "/s3d1/s3d2";
 static const char dir_s3d3[] = TMP_DIR "/s3d1/s3d2/s3d3";
+static const char file1_s3d3[] = TMP_DIR "/s3d1/s3d2/s3d3/f1";
+static const char file1_s3d4[] = TMP_DIR "/s3d1/s3d2/s3d4/f1";
 
 /*
  * layout1 hierarchy:

@@ -348,7 +350,8 @@ static void create_layout1(struct __test_metadata *const _metadata)
 	ASSERT_EQ(0, mount_opt(&mnt_tmp, dir_s3d2));
 	clear_cap(_metadata, CAP_SYS_ADMIN);
 
-	ASSERT_EQ(0, mkdir(dir_s3d3, 0700));
+	create_file(_metadata, file1_s3d3);
+	create_file(_metadata, file1_s3d4);
 }
 
 static void remove_layout1(struct __test_metadata *const _metadata)

@@ -368,7 +371,8 @@ static void remove_layout1(struct __test_metadata *const _metadata)
 	EXPECT_EQ(0, remove_path(dir_s2d2));
 
 	EXPECT_EQ(0, remove_path(file1_s3d1));
-	EXPECT_EQ(0, remove_path(dir_s3d3));
+	EXPECT_EQ(0, remove_path(file1_s3d3));
+	EXPECT_EQ(0, remove_path(file1_s3d4));
 	set_cap(_metadata, CAP_SYS_ADMIN);
 	umount(dir_s3d2);
 	clear_cap(_metadata, CAP_SYS_ADMIN);

@@ -710,6 +714,27 @@ static void enforce_ruleset(struct __test_metadata *const _metadata,
 	}
 }
 
+static void enforce_fs(struct __test_metadata *const _metadata,
+		       const __u64 access_fs, const struct rule rules[])
+{
+	int ruleset_fd;
+
+	if (rules) {
+		ruleset_fd = create_ruleset(_metadata, access_fs, rules);
+	} else {
+		const struct landlock_ruleset_attr ruleset_attr = {
+			.handled_access_fs = access_fs,
+		};
+
+		ruleset_fd = landlock_create_ruleset(&ruleset_attr,
+						     sizeof(ruleset_attr), 0);
+		ASSERT_LE(0, ruleset_fd);
+	}
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+}
+
 TEST_F_FORK(layout0, proc_nsfs)
 {
 	const struct rule rules[] = {

@@ -2086,6 +2111,170 @@ TEST_F_FORK(layout1, rename_file)
 			       RENAME_EXCHANGE));
 }
 
+TEST_F_FORK(layout1, rename_whiteout_denied)
+{
+	/* The affected file is a FIFO. */
+	ASSERT_EQ(0, unlink(file1_s3d3));
+	ASSERT_EQ(0, mknod(file1_s3d3, S_IFIFO | 0600, 0));
+
+	/* Deny MAKE_REG, but allow MAKE_FIFO. */
+	enforce_fs(_metadata, LANDLOCK_ACCESS_FS_MAKE_REG, NULL);
+
+	/*
+	 * Try to rename a file with RENAME_WHITEOUT.
+	 * file1_s3d3 is in dir_s3d2 (tmpfs), so it supports RENAME_WHITEOUT.
+	 * Denied, because whiteout creation is guarded with MAKE_REG.
+	 */
+	EXPECT_EQ(-1, renameat2(AT_FDCWD, file1_s3d3, AT_FDCWD,
+				TMP_DIR "/s3d1/s3d2/s3d3/f2", RENAME_WHITEOUT));
+	EXPECT_EQ(EACCES, errno);
+}
+
+static bool is_whiteout(const char *const path)
+{
+	struct stat st;
+
+	if (stat(path, &st) == -1)
+		return false;
+
+	return S_ISCHR(st.st_mode) && st.st_rdev == makedev(0, 0);
+}
+
+static bool is_fifo(const char *const path)
+{
+	struct stat st;
+
+	return stat(path, &st) == 0 && S_ISFIFO(st.st_mode);
+}
+
+TEST_F_FORK(layout1, rename_whiteout_allowed)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s3d3,
+			.access = LANDLOCK_ACCESS_FS_MAKE_REG,
+		},
+		{},
+	};
+
+	/* The affected file is a FIFO. */
+	ASSERT_EQ(0, unlink(file1_s3d3));
+	ASSERT_EQ(0, mknod(file1_s3d3, S_IFIFO | 0600, 0));
+
+	/* Allow MAKE_REG below dir_s3d3. */
+	enforce_fs(_metadata, LANDLOCK_ACCESS_FS_MAKE_REG, rules);
+
+	/*
+	 * Rename a file with RENAME_WHITEOUT within the same directory.
+	 * Allowed, because MAKE_REG is granted for the whiteout object which
+	 * gets created in the source location.
+	 */
+	EXPECT_EQ(0, renameat2(AT_FDCWD, file1_s3d3, AT_FDCWD,
+			       TMP_DIR "/s3d1/s3d2/s3d3/f2", RENAME_WHITEOUT));
+
+	/* A whiteout object took the place of the moved FIFO. */
+	EXPECT_TRUE(is_whiteout(file1_s3d3));
+	EXPECT_TRUE(is_fifo(TMP_DIR "/s3d1/s3d2/s3d3/f2"));
+}
+
+TEST_F_FORK(layout1, rename_whiteout_reparenting)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s3d2,
+			.access = LANDLOCK_ACCESS_FS_REFER,
+		},
+		{
+			.path = dir_s3d3,
+			.access = LANDLOCK_ACCESS_FS_MAKE_REG,
+		},
+		{},
+	};
+
+	/* The moved files are FIFOs. */
+	ASSERT_EQ(0, unlink(file1_s3d3));
+	ASSERT_EQ(0, mknod(file1_s3d3, S_IFIFO | 0600, 0));
+	ASSERT_EQ(0, unlink(file1_s3d4));
+	ASSERT_EQ(0, mknod(file1_s3d4, S_IFIFO | 0600, 0));
+
+	/* Allow REFER below dir_s3d2, but MAKE_REG only below dir_s3d3. */
+	enforce_fs(_metadata,
+		   LANDLOCK_ACCESS_FS_MAKE_REG | LANDLOCK_ACCESS_FS_REFER,
+		   rules);
+
+	/*
+	 * The whiteout object is created in the source directory: Moving the
+	 * FIFO out of dir_s3d4 is denied because MAKE_REG is not granted
+	 * there, even though it is granted in the destination directory
+	 * dir_s3d3.
+	 */
+	EXPECT_EQ(-1, renameat2(AT_FDCWD, file1_s3d4, AT_FDCWD,
+				TMP_DIR "/s3d1/s3d2/s3d3/f2", RENAME_WHITEOUT));
+	EXPECT_EQ(EACCES, errno);
+
+	/*
+	 * Moving the FIFO out of dir_s3d3 is allowed, because MAKE_REG is
+	 * granted there for the created whiteout object.
+	 */
+	EXPECT_EQ(0, renameat2(AT_FDCWD, file1_s3d3, AT_FDCWD,
+			       TMP_DIR "/s3d1/s3d2/s3d4/f2", RENAME_WHITEOUT));
+
+	/* A whiteout object took the place of the moved FIFO. */
+	EXPECT_TRUE(is_whiteout(file1_s3d3));
+	EXPECT_TRUE(is_fifo(TMP_DIR "/s3d1/s3d2/s3d4/f2"));
+}
+
+TEST_F_FORK(layout1, rename_whiteout_exchange)
+{
+	const char *const whiteout_s3d3 = TMP_DIR "/s3d1/s3d2/s3d3/f2";
+	const struct rule rules[] = {
+		{
+			.path = dir_s3d2,
+			.access = LANDLOCK_ACCESS_FS_REFER,
+		},
+		{
+			.path = dir_s3d3,
+			.access = LANDLOCK_ACCESS_FS_MAKE_REG,
+		},
+		{},
+	};
+
+	/* The exchanged files are FIFOs and an existing whiteout object. */
+	ASSERT_EQ(0, unlink(file1_s3d3));
+	ASSERT_EQ(0, mknod(file1_s3d3, S_IFIFO | 0600, 0));
+	ASSERT_EQ(0, mknod(whiteout_s3d3, S_IFCHR | 0600, makedev(0, 0)));
+	ASSERT_EQ(0, unlink(file1_s3d4));
+	ASSERT_EQ(0, mknod(file1_s3d4, S_IFIFO | 0600, 0));
+
+	/* Allow REFER below dir_s3d2, but MAKE_REG only below dir_s3d3. */
+	enforce_fs(_metadata,
+		   LANDLOCK_ACCESS_FS_MAKE_REG | LANDLOCK_ACCESS_FS_REFER,
+		   rules);
+
+	/*
+	 * With RENAME_EXCHANGE, the whiteout object moves into the source
+	 * directory of the rename: Exchanging the FIFO in dir_s3d4 with the
+	 * whiteout object is denied because MAKE_REG is not granted in
+	 * dir_s3d4, even though it is granted in the whiteout object's own
+	 * directory dir_s3d3.
+	 */
+	EXPECT_EQ(-1, renameat2(AT_FDCWD, file1_s3d4, AT_FDCWD, whiteout_s3d3,
+				RENAME_EXCHANGE));
+	EXPECT_EQ(EACCES, errno);
+
+	/*
+	 * Exchanging the FIFO in dir_s3d3 with the whiteout object is
+	 * allowed, because MAKE_REG is granted in the directory into which
+	 * the whiteout object moves.
+	 */
+	EXPECT_EQ(0, renameat2(AT_FDCWD, file1_s3d3, AT_FDCWD, whiteout_s3d3,
+			       RENAME_EXCHANGE));
+
+	/* The FIFO and the whiteout object swapped places. */
+	EXPECT_TRUE(is_whiteout(file1_s3d3));
+	EXPECT_TRUE(is_fifo(whiteout_s3d3));
+}
+
 TEST_F_FORK(layout1, rename_dir)
 {
 	const struct rule rules[] = {

@@ -3139,6 +3328,18 @@ TEST_F_FORK(layout1, make_char)
 		       makedev(1, 3));
 }
 
+TEST_F_FORK(layout1, make_whiteout)
+{
+	/*
+	 * Creates a whiteout object (creation guarded by MAKE_REG).
+	 *
+	 * Contrary to the other character devices, this does not require
+	 * CAP_MKNOD, cf. vfs_mknod().
+	 */
+	test_make_file(_metadata, LANDLOCK_ACCESS_FS_MAKE_REG, S_IFCHR,
+		       makedev(0, 0));
+}
+
 TEST_F_FORK(layout1, make_block)
 {
 	/* Creates a /dev/loop0 device. */

index a085dd88fd11..ffb5af406b86 100644
@@ -51,6 +51,10 @@ int open_tree(int dfd, const char *filename, unsigned int flags)
 #define RENAME_EXCHANGE (1 << 1)
 #endif
 
+#ifndef RENAME_WHITEOUT
+#define RENAME_WHITEOUT (1 << 2)
+#endif
+
 #define TMP_DIR "tmp"
 #define BINARY_PATH "./true"
 

@@ -78,6 +82,8 @@ static const char file1_s3d1[] = TMP_DIR "/s3d1/f1";
 /* dir_s3d2 is a mount point. */
 static const char dir_s3d2[] = TMP_DIR "/s3d1/s3d2";
 static const char dir_s3d3[] = TMP_DIR "/s3d1/s3d2/s3d3";
+static const char file1_s3d3[] = TMP_DIR "/s3d1/s3d2/s3d3/f1";
+static const char file1_s3d4[] = TMP_DIR "/s3d1/s3d2/s3d4/f1";
 
 /*
  * layout1 hierarchy:

@@ -353,7 +359,8 @@ static void create_layout1(struct __test_metadata *const _metadata)
 	ASSERT_EQ(0, mount_opt(&mnt_tmp, dir_s3d2));
 	clear_cap(_metadata, CAP_SYS_ADMIN);
 
-	ASSERT_EQ(0, mkdir(dir_s3d3, 0700));
+	create_file(_metadata, file1_s3d3);
+	create_file(_metadata, file1_s3d4);
 }
 
 static void remove_layout1(struct __test_metadata *const _metadata)

@@ -373,7 +380,8 @@ static void remove_layout1(struct __test_metadata *const _metadata)
 	EXPECT_EQ(0, remove_path(dir_s2d2));
 
 	EXPECT_EQ(0, remove_path(file1_s3d1));
-	EXPECT_EQ(0, remove_path(dir_s3d3));
+	EXPECT_EQ(0, remove_path(file1_s3d3));
+	EXPECT_EQ(0, remove_path(file1_s3d4));
 	set_cap(_metadata, CAP_SYS_ADMIN);
 	umount(dir_s3d2);
 	clear_cap(_metadata, CAP_SYS_ADMIN);

@@ -715,6 +723,27 @@ static void enforce_ruleset(struct __test_metadata *const _metadata,
 	}
 }
 
+static void enforce_fs(struct __test_metadata *const _metadata,
+		       const __u64 access_fs, const struct rule rules[])
+{
+	int ruleset_fd;
+
+	if (rules) {
+		ruleset_fd = create_ruleset(_metadata, access_fs, rules);
+	} else {
+		const struct landlock_ruleset_attr ruleset_attr = {
+			.handled_access_fs = access_fs,
+		};
+
+		ruleset_fd = landlock_create_ruleset(&ruleset_attr,
+						     sizeof(ruleset_attr), 0);
+		ASSERT_LE(0, ruleset_fd);
+	}
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+}
+
 TEST_F_FORK(layout0, proc_nsfs)
 {
 	const struct rule rules[] = {

@@ -2091,6 +2120,170 @@ TEST_F_FORK(layout1, rename_file)
 			       RENAME_EXCHANGE));
 }
 
+TEST_F_FORK(layout1, rename_whiteout_denied)
+{
+	/* The affected file is a FIFO. */
+	ASSERT_EQ(0, unlink(file1_s3d3));
+	ASSERT_EQ(0, mknod(file1_s3d3, S_IFIFO | 0600, 0));
+
+	/* Deny MAKE_REG, but allow MAKE_FIFO. */
+	enforce_fs(_metadata, LANDLOCK_ACCESS_FS_MAKE_REG, NULL);
+
+	/*
+	 * Try to rename a file with RENAME_WHITEOUT.
+	 * file1_s3d3 is in dir_s3d2 (tmpfs), so it supports RENAME_WHITEOUT.
+	 * Denied, because whiteout creation is guarded with MAKE_REG.
+	 */
+	EXPECT_EQ(-1, renameat2(AT_FDCWD, file1_s3d3, AT_FDCWD,
+				TMP_DIR "/s3d1/s3d2/s3d3/f2", RENAME_WHITEOUT));
+	EXPECT_EQ(EACCES, errno);
+}
+
+static bool is_whiteout(const char *const path)
+{
+	struct stat st;
+
+	if (stat(path, &st) == -1)
+		return false;
+
+	return S_ISCHR(st.st_mode) && st.st_rdev == makedev(0, 0);
+}
+
+static bool is_fifo(const char *const path)
+{
+	struct stat st;
+
+	return stat(path, &st) == 0 && S_ISFIFO(st.st_mode);
+}
+
+TEST_F_FORK(layout1, rename_whiteout_allowed)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s3d3,
+			.access = LANDLOCK_ACCESS_FS_MAKE_REG,
+		},
+		{},
+	};
+
+	/* The affected file is a FIFO. */
+	ASSERT_EQ(0, unlink(file1_s3d3));
+	ASSERT_EQ(0, mknod(file1_s3d3, S_IFIFO | 0600, 0));
+
+	/* Allow MAKE_REG below dir_s3d3. */
+	enforce_fs(_metadata, LANDLOCK_ACCESS_FS_MAKE_REG, rules);
+
+	/*
+	 * Rename a file with RENAME_WHITEOUT within the same directory.
+	 * Allowed, because MAKE_REG is granted for the whiteout object which
+	 * gets created in the source location.
+	 */
+	EXPECT_EQ(0, renameat2(AT_FDCWD, file1_s3d3, AT_FDCWD,
+			       TMP_DIR "/s3d1/s3d2/s3d3/f2", RENAME_WHITEOUT));
+
+	/* A whiteout object took the place of the moved FIFO. */
+	EXPECT_TRUE(is_whiteout(file1_s3d3));
+	EXPECT_TRUE(is_fifo(TMP_DIR "/s3d1/s3d2/s3d3/f2"));
+}
+
+TEST_F_FORK(layout1, rename_whiteout_reparenting)
+{
+	const struct rule rules[] = {
+		{
+			.path = dir_s3d2,
+			.access = LANDLOCK_ACCESS_FS_REFER,
+		},
+		{
+			.path = dir_s3d3,
+			.access = LANDLOCK_ACCESS_FS_MAKE_REG,
+		},
+		{},
+	};
+
+	/* The moved files are FIFOs. */
+	ASSERT_EQ(0, unlink(file1_s3d3));
+	ASSERT_EQ(0, mknod(file1_s3d3, S_IFIFO | 0600, 0));
+	ASSERT_EQ(0, unlink(file1_s3d4));
+	ASSERT_EQ(0, mknod(file1_s3d4, S_IFIFO | 0600, 0));
+
+	/* Allow REFER below dir_s3d2, but MAKE_REG only below dir_s3d3. */
+	enforce_fs(_metadata,
+		   LANDLOCK_ACCESS_FS_MAKE_REG | LANDLOCK_ACCESS_FS_REFER,
+		   rules);
+
+	/*
+	 * The whiteout object is created in the source directory: Moving the
+	 * FIFO out of dir_s3d4 is denied because MAKE_REG is not granted
+	 * there, even though it is granted in the destination directory
+	 * dir_s3d3.
+	 */
+	EXPECT_EQ(-1, renameat2(AT_FDCWD, file1_s3d4, AT_FDCWD,
+				TMP_DIR "/s3d1/s3d2/s3d3/f2", RENAME_WHITEOUT));
+	EXPECT_EQ(EACCES, errno);
+
+	/*
+	 * Moving the FIFO out of dir_s3d3 is allowed, because MAKE_REG is
+	 * granted there for the created whiteout object.
+	 */
+	EXPECT_EQ(0, renameat2(AT_FDCWD, file1_s3d3, AT_FDCWD,
+			       TMP_DIR "/s3d1/s3d2/s3d4/f2", RENAME_WHITEOUT));
+
+	/* A whiteout object took the place of the moved FIFO. */
+	EXPECT_TRUE(is_whiteout(file1_s3d3));
+	EXPECT_TRUE(is_fifo(TMP_DIR "/s3d1/s3d2/s3d4/f2"));
+}
+
+TEST_F_FORK(layout1, rename_whiteout_exchange)
+{
+	const char *const whiteout_s3d3 = TMP_DIR "/s3d1/s3d2/s3d3/f2";
+	const struct rule rules[] = {
+		{
+			.path = dir_s3d2,
+			.access = LANDLOCK_ACCESS_FS_REFER,
+		},
+		{
+			.path = dir_s3d3,
+			.access = LANDLOCK_ACCESS_FS_MAKE_REG,
+		},
+		{},
+	};
+
+	/* The exchanged files are FIFOs and an existing whiteout object. */
+	ASSERT_EQ(0, unlink(file1_s3d3));
+	ASSERT_EQ(0, mknod(file1_s3d3, S_IFIFO | 0600, 0));
+	ASSERT_EQ(0, mknod(whiteout_s3d3, S_IFCHR | 0600, makedev(0, 0)));
+	ASSERT_EQ(0, unlink(file1_s3d4));
+	ASSERT_EQ(0, mknod(file1_s3d4, S_IFIFO | 0600, 0));
+
+	/* Allow REFER below dir_s3d2, but MAKE_REG only below dir_s3d3. */
+	enforce_fs(_metadata,
+		   LANDLOCK_ACCESS_FS_MAKE_REG | LANDLOCK_ACCESS_FS_REFER,
+		   rules);
+
+	/*
+	 * With RENAME_EXCHANGE, the whiteout object moves into the source
+	 * directory of the rename: Exchanging the FIFO in dir_s3d4 with the
+	 * whiteout object is denied because MAKE_REG is not granted in
+	 * dir_s3d4, even though it is granted in the whiteout object's own
+	 * directory dir_s3d3.
+	 */
+	EXPECT_EQ(-1, renameat2(AT_FDCWD, file1_s3d4, AT_FDCWD, whiteout_s3d3,
+				RENAME_EXCHANGE));
+	EXPECT_EQ(EACCES, errno);
+
+	/*
+	 * Exchanging the FIFO in dir_s3d3 with the whiteout object is
+	 * allowed, because MAKE_REG is granted in the directory into which
+	 * the whiteout object moves.
+	 */
+	EXPECT_EQ(0, renameat2(AT_FDCWD, file1_s3d3, AT_FDCWD, whiteout_s3d3,
+			       RENAME_EXCHANGE));
+
+	/* The FIFO and the whiteout object swapped places. */
+	EXPECT_TRUE(is_whiteout(file1_s3d3));
+	EXPECT_TRUE(is_fifo(whiteout_s3d3));
+}
+
 TEST_F_FORK(layout1, rename_dir)
 {
 	const struct rule rules[] = {

@@ -3144,6 +3337,18 @@ TEST_F_FORK(layout1, make_char)
 		       makedev(1, 3));
 }
 
+TEST_F_FORK(layout1, make_whiteout)
+{
+	/*
+	 * Creates a whiteout object (creation guarded by MAKE_REG).
+	 *
+	 * Contrary to the other character devices, this does not require
+	 * CAP_MKNOD, cf. vfs_mknod().
+	 */
+	test_make_file(_metadata, LANDLOCK_ACCESS_FS_MAKE_REG, S_IFCHR,
+		       makedev(0, 0));
+}
+
 TEST_F_FORK(layout1, make_block)
 {
 	/* Creates a /dev/loop0 device. */