Merge tag 'landlock-5.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/mic/linux

Pull Landlock updates from Mickaël Salaün:

 - improve the path_rename LSM hook implementations for RENAME_EXCHANGE;

 - fix a too-restrictive filesystem control for a rare corner case;

 - set the nested sandbox limitation to 16 layers;

 - add a new LANDLOCK_ACCESS_FS_REFER access right to properly handle
   file reparenting (i.e. full rename and link support);

 - add new tests and documentation;

 - format code with clang-format to make it easier to maintain and
   contribute.

* tag 'landlock-5.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/mic/linux: (30 commits)
  landlock: Explain how to support Landlock
  landlock: Add design choices documentation for filesystem access rights
  landlock: Document good practices about filesystem policies
  landlock: Document LANDLOCK_ACCESS_FS_REFER and ABI versioning
  samples/landlock: Add support for file reparenting
  selftests/landlock: Add 11 new test suites dedicated to file reparenting
  landlock: Add support for file reparenting with LANDLOCK_ACCESS_FS_REFER
  LSM: Remove double path_rename hook calls for RENAME_EXCHANGE
  landlock: Move filesystem helpers and add a new one
  landlock: Fix same-layer rule unions
  landlock: Create find_rule() from unmask_layers()
  landlock: Reduce the maximum number of layers to 16
  landlock: Define access_mask_t to enforce a consistent access mask size
  selftests/landlock: Test landlock_create_ruleset(2) argument check ordering
  landlock: Change landlock_restrict_self(2) check ordering
  landlock: Change landlock_add_rule(2) argument check ordering
  selftests/landlock: Add tests for O_PATH
  selftests/landlock: Fully test file rename with "remove" access
  selftests/landlock: Extend access right tests to directories
  selftests/landlock: Add tests for unknown access rights
  ...

1 files changed, 81 insertions, 51 deletions

diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index 8859fc193542..3e404e51ec64 100644
--- a/samples/landlock/sandboxer.c
+++ b/samples/landlock/sandboxer.c
@@ -22,9 +22,9 @@
 #include <unistd.h>
 
 #ifndef landlock_create_ruleset
-static inline int landlock_create_ruleset(
-		const struct landlock_ruleset_attr *const attr,
-		const size_t size, const __u32 flags)
+static inline int
+landlock_create_ruleset(const struct landlock_ruleset_attr *const attr,
+			const size_t size, const __u32 flags)
 {
 	return syscall(__NR_landlock_create_ruleset, attr, size, flags);
 }
@@ -32,17 +32,18 @@ static inline int landlock_create_ruleset(
 
 #ifndef landlock_add_rule
 static inline int landlock_add_rule(const int ruleset_fd,
-		const enum landlock_rule_type rule_type,
-		const void *const rule_attr, const __u32 flags)
+				    const enum landlock_rule_type rule_type,
+				    const void *const rule_attr,
+				    const __u32 flags)
 {
-	return syscall(__NR_landlock_add_rule, ruleset_fd, rule_type,
-			rule_attr, flags);
+	return syscall(__NR_landlock_add_rule, ruleset_fd, rule_type, rule_attr,
+		       flags);
 }
 #endif
 
 #ifndef landlock_restrict_self
 static inline int landlock_restrict_self(const int ruleset_fd,
-		const __u32 flags)
+					 const __u32 flags)
 {
 	return syscall(__NR_landlock_restrict_self, ruleset_fd, flags);
 }
@@ -70,14 +71,17 @@ static int parse_path(char *env_path, const char ***const path_list)
 	return num_paths;
 }
 
+/* clang-format off */
+
 #define ACCESS_FILE ( \
 	LANDLOCK_ACCESS_FS_EXECUTE | \
 	LANDLOCK_ACCESS_FS_WRITE_FILE | \
 	LANDLOCK_ACCESS_FS_READ_FILE)
 
-static int populate_ruleset(
-		const char *const env_var, const int ruleset_fd,
-		const __u64 allowed_access)
+/* clang-format on */
+
+static int populate_ruleset(const char *const env_var, const int ruleset_fd,
+			    const __u64 allowed_access)
 {
 	int num_paths, i, ret = 1;
 	char *env_path_name;
@@ -107,12 +111,10 @@ static int populate_ruleset(
 	for (i = 0; i < num_paths; i++) {
 		struct stat statbuf;
 
-		path_beneath.parent_fd = open(path_list[i], O_PATH |
-				O_CLOEXEC);
+		path_beneath.parent_fd = open(path_list[i], O_PATH | O_CLOEXEC);
 		if (path_beneath.parent_fd < 0) {
 			fprintf(stderr, "Failed to open \"%s\": %s\n",
-					path_list[i],
-					strerror(errno));
+				path_list[i], strerror(errno));
 			goto out_free_name;
 		}
 		if (fstat(path_beneath.parent_fd, &statbuf)) {
@@ -123,9 +125,10 @@ static int populate_ruleset(
 		if (!S_ISDIR(statbuf.st_mode))
 			path_beneath.allowed_access &= ACCESS_FILE;
 		if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
-					&path_beneath, 0)) {
-			fprintf(stderr, "Failed to update the ruleset with \"%s\": %s\n",
-					path_list[i], strerror(errno));
+				      &path_beneath, 0)) {
+			fprintf(stderr,
+				"Failed to update the ruleset with \"%s\": %s\n",
+				path_list[i], strerror(errno));
 			close(path_beneath.parent_fd);
 			goto out_free_name;
 		}
@@ -139,6 +142,8 @@ out_free_name:
 	return ret;
 }
 
+/* clang-format off */
+
 #define ACCESS_FS_ROUGHLY_READ ( \
 	LANDLOCK_ACCESS_FS_EXECUTE | \
 	LANDLOCK_ACCESS_FS_READ_FILE | \
@@ -154,64 +159,89 @@ out_free_name:
 	LANDLOCK_ACCESS_FS_MAKE_SOCK | \
 	LANDLOCK_ACCESS_FS_MAKE_FIFO | \
 	LANDLOCK_ACCESS_FS_MAKE_BLOCK | \
-	LANDLOCK_ACCESS_FS_MAKE_SYM)
+	LANDLOCK_ACCESS_FS_MAKE_SYM | \
+	LANDLOCK_ACCESS_FS_REFER)
+
+#define ACCESS_ABI_2 ( \
+	LANDLOCK_ACCESS_FS_REFER)
+
+/* clang-format on */
 
 int main(const int argc, char *const argv[], char *const *const envp)
 {
 	const char *cmd_path;
 	char *const *cmd_argv;
-	int ruleset_fd;
+	int ruleset_fd, abi;
+	__u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ,
+	      access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE;
 	struct landlock_ruleset_attr ruleset_attr = {
-		.handled_access_fs = ACCESS_FS_ROUGHLY_READ |
-			ACCESS_FS_ROUGHLY_WRITE,
+		.handled_access_fs = access_fs_rw,
 	};
 
 	if (argc < 2) {
-		fprintf(stderr, "usage: %s=\"...\" %s=\"...\" %s <cmd> [args]...\n\n",
-				ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
-		fprintf(stderr, "Launch a command in a restricted environment.\n\n");
+		fprintf(stderr,
+			"usage: %s=\"...\" %s=\"...\" %s <cmd> [args]...\n\n",
+			ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
+		fprintf(stderr,
+			"Launch a command in a restricted environment.\n\n");
 		fprintf(stderr, "Environment variables containing paths, "
 				"each separated by a colon:\n");
-		fprintf(stderr, "* %s: list of paths allowed to be used in a read-only way.\n",
-				ENV_FS_RO_NAME);
-		fprintf(stderr, "* %s: list of paths allowed to be used in a read-write way.\n",
-				ENV_FS_RW_NAME);
-		fprintf(stderr, "\nexample:\n"
-				"%s=\"/bin:/lib:/usr:/proc:/etc:/dev/urandom\" "
-				"%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
-				"%s bash -i\n",
-				ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
+		fprintf(stderr,
+			"* %s: list of paths allowed to be used in a read-only way.\n",
+			ENV_FS_RO_NAME);
+		fprintf(stderr,
+			"* %s: list of paths allowed to be used in a read-write way.\n",
+			ENV_FS_RW_NAME);
+		fprintf(stderr,
+			"\nexample:\n"
+			"%s=\"/bin:/lib:/usr:/proc:/etc:/dev/urandom\" "
+			"%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
+			"%s bash -i\n",
+			ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
 		return 1;
 	}
 
-	ruleset_fd = landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
-	if (ruleset_fd < 0) {
+	abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION);
+	if (abi < 0) {
 		const int err = errno;
 
-		perror("Failed to create a ruleset");
+		perror("Failed to check Landlock compatibility");
 		switch (err) {
 		case ENOSYS:
-			fprintf(stderr, "Hint: Landlock is not supported by the current kernel. "
-					"To support it, build the kernel with "
-					"CONFIG_SECURITY_LANDLOCK=y and prepend "
-					"\"landlock,\" to the content of CONFIG_LSM.\n");
+			fprintf(stderr,
+				"Hint: Landlock is not supported by the current kernel. "
+				"To support it, build the kernel with "
+				"CONFIG_SECURITY_LANDLOCK=y and prepend "
+				"\"landlock,\" to the content of CONFIG_LSM.\n");
 			break;
 		case EOPNOTSUPP:
-			fprintf(stderr, "Hint: Landlock is currently disabled. "
-					"It can be enabled in the kernel configuration by "
-					"prepending \"landlock,\" to the content of CONFIG_LSM, "
-					"or at boot time by setting the same content to the "
-					"\"lsm\" kernel parameter.\n");
+			fprintf(stderr,
+				"Hint: Landlock is currently disabled. "
+				"It can be enabled in the kernel configuration by "
+				"prepending \"landlock,\" to the content of CONFIG_LSM, "
+				"or at boot time by setting the same content to the "
+				"\"lsm\" kernel parameter.\n");
 			break;
 		}
 		return 1;
 	}
-	if (populate_ruleset(ENV_FS_RO_NAME, ruleset_fd,
-				ACCESS_FS_ROUGHLY_READ)) {
+	/* Best-effort security. */
+	if (abi < 2) {
+		ruleset_attr.handled_access_fs &= ~ACCESS_ABI_2;
+		access_fs_ro &= ~ACCESS_ABI_2;
+		access_fs_rw &= ~ACCESS_ABI_2;
+	}
+
+	ruleset_fd =
+		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+	if (ruleset_fd < 0) {
+		perror("Failed to create a ruleset");
+		return 1;
+	}
+	if (populate_ruleset(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) {
 		goto err_close_ruleset;
 	}
-	if (populate_ruleset(ENV_FS_RW_NAME, ruleset_fd,
-				ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE)) {
+	if (populate_ruleset(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) {
 		goto err_close_ruleset;
 	}
 	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
@@ -228,7 +258,7 @@ int main(const int argc, char *const argv[], char *const *const envp)
 	cmd_argv = argv + 1;
 	execvpe(cmd_path, cmd_argv, envp);
 	fprintf(stderr, "Failed to execute \"%s\": %s\n", cmd_path,
-			strerror(errno));
+		strerror(errno));
 	fprintf(stderr, "Hint: access to the binary, the interpreter or "
 			"shared libraries may be denied.\n");
 	return 1;