Re: [PATCH -next v2 3/6] landlock: add chmod and chown support

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Hi,

在 2022/8/27 19:12, Xiu Jianfeng 写道:
Add two flags LANDLOCK_ACCESS_FS_CHMOD and LANDLOCK_ACCESS_FS_CHGRP to
support restriction to chmod(2) and chown(2) with landlock.

If these two access rights are set on a directory, they only take effect
for its context, not the directory itself.

This patch also change the landlock ABI version from 3 to 4.

Signed-off-by: Xiu Jianfeng <xiujianfeng@xxxxxxxxxx>
---
  include/uapi/linux/landlock.h                | 10 +++--
  security/landlock/fs.c                       | 43 +++++++++++++++++++-
  security/landlock/limits.h                   |  2 +-
  security/landlock/syscalls.c                 |  2 +-
  tools/testing/selftests/landlock/base_test.c |  2 +-
  tools/testing/selftests/landlock/fs_test.c   |  6 ++-
  6 files changed, 56 insertions(+), 9 deletions(-)

diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
index 735b1fe8326e..07b73626ff20 100644
--- a/include/uapi/linux/landlock.h
+++ b/include/uapi/linux/landlock.h
@@ -141,14 +141,16 @@ struct landlock_path_beneath_attr {
   *   directory) parent.  Otherwise, such actions are denied with errno set to
   *   EACCES.  The EACCES errno prevails over EXDEV to let user space
   *   efficiently deal with an unrecoverable error.
+ * - %LANDLOCK_ACCESS_FS_CHMOD: Change the file mode bits of a file.
+ * - %LANDLOCK_ACCESS_FS_CHGRP: Change the owner and/or group of a file.
   *
   * .. warning::
   *
   *   It is currently not possible to restrict some file-related actions
   *   accessible through these syscall families: :manpage:`chdir(2)`,
- *   :manpage:`stat(2)`, :manpage:`flock(2)`, :manpage:`chmod(2)`,
- *   :manpage:`chown(2)`, :manpage:`setxattr(2)`, :manpage:`utime(2)`,
- *   :manpage:`ioctl(2)`, :manpage:`fcntl(2)`, :manpage:`access(2)`.
+ *   :manpage:`stat(2)`, :manpage:`flock(2)`, :manpage:`setxattr(2)`,
+ *   :manpage:`utime(2)`,:manpage:`ioctl(2)`, :manpage:`fcntl(2)`,
+ *   :manpage:`access(2)`.
   *   Future Landlock evolutions will enable to restrict them.
   */
  /* clang-format off */
@@ -167,6 +169,8 @@ struct landlock_path_beneath_attr {
  #define LANDLOCK_ACCESS_FS_MAKE_SYM			(1ULL << 12)
  #define LANDLOCK_ACCESS_FS_REFER			(1ULL << 13)
  #define LANDLOCK_ACCESS_FS_TRUNCATE			(1ULL << 14)
+#define LANDLOCK_ACCESS_FS_CHMOD			(1ULL << 15)
+#define LANDLOCK_ACCESS_FS_CHGRP			(1ULL << 16)
  /* clang-format on */
#endif /* _UAPI_LINUX_LANDLOCK_H */
diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 4ef614a4ea22..6ac83d96ada7 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -185,7 +185,9 @@ static struct landlock_object *get_inode_object(struct inode *const inode)
  	LANDLOCK_ACCESS_FS_EXECUTE | \
  	LANDLOCK_ACCESS_FS_WRITE_FILE | \
  	LANDLOCK_ACCESS_FS_READ_FILE | \
-	LANDLOCK_ACCESS_FS_TRUNCATE)
+	LANDLOCK_ACCESS_FS_TRUNCATE | \
+	LANDLOCK_ACCESS_FS_CHMOD | \
+	LANDLOCK_ACCESS_FS_CHGRP)
  /* clang-format on */
/*
@@ -690,6 +692,31 @@ static inline int current_check_access_path(const struct path *const path,
  	return check_access_path(dom, path, access_request);
  }
+static inline int
+current_check_access_path_context_only(const struct path *const path,
+				       const access_mask_t access_request)
+{
+	const struct landlock_ruleset *const dom =
+		landlock_get_current_domain();
+	struct path eff_path;
+	int ret;
+
+	if (!dom)
+		return 0;
+	eff_path = *path;
+	/* if it's dir, check its visible parent. */
+	if (d_is_dir(eff_path.dentry)) {
+		path_get(&eff_path);
+		/* dont care if reaches the root or not. */

I may made a mistake here, I think it should return -EACCES directly if the walk result is not WALK_CONTINUE.

+		walk_to_visible_parent(&eff_path);
+		ret = current_check_access_path(&eff_path, access_request);
+		path_put(&eff_path);
+	} else {
+		ret = current_check_access_path(&eff_path, access_request);
+	}
+	return ret;
+}
+
  static inline access_mask_t get_mode_access(const umode_t mode)
  {
  	switch (mode & S_IFMT) {
@@ -1177,6 +1204,18 @@ static int hook_path_truncate(const struct path *const path)
  	return current_check_access_path(path, LANDLOCK_ACCESS_FS_TRUNCATE);
  }
+static int hook_path_chmod(const struct path *const path, umode_t mode)
+{
+	return current_check_access_path_context_only(path,
+					LANDLOCK_ACCESS_FS_CHMOD);
+}
+
+static int hook_path_chown(const struct path *const path, kuid_t uid, kgid_t gid)
+{
+	return current_check_access_path_context_only(path,
+					LANDLOCK_ACCESS_FS_CHGRP);
+}
+
  /* File hooks */
static inline access_mask_t get_file_access(const struct file *const file)
@@ -1230,6 +1269,8 @@ static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
  	LSM_HOOK_INIT(path_unlink, hook_path_unlink),
  	LSM_HOOK_INIT(path_rmdir, hook_path_rmdir),
  	LSM_HOOK_INIT(path_truncate, hook_path_truncate),
+	LSM_HOOK_INIT(path_chmod, hook_path_chmod),
+	LSM_HOOK_INIT(path_chown, hook_path_chown),
LSM_HOOK_INIT(file_open, hook_file_open),
  };
diff --git a/security/landlock/limits.h b/security/landlock/limits.h
index 82288f0e9e5e..7cdd7d467d12 100644
--- a/security/landlock/limits.h
+++ b/security/landlock/limits.h
@@ -18,7 +18,7 @@
  #define LANDLOCK_MAX_NUM_LAYERS		16
  #define LANDLOCK_MAX_NUM_RULES		U32_MAX
-#define LANDLOCK_LAST_ACCESS_FS LANDLOCK_ACCESS_FS_TRUNCATE
+#define LANDLOCK_LAST_ACCESS_FS		LANDLOCK_ACCESS_FS_CHGRP
  #define LANDLOCK_MASK_ACCESS_FS		((LANDLOCK_LAST_ACCESS_FS << 1) - 1)
  #define LANDLOCK_NUM_ACCESS_FS		__const_hweight64(LANDLOCK_MASK_ACCESS_FS)
diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
index f4d6fc7ed17f..469e0e11735c 100644
--- a/security/landlock/syscalls.c
+++ b/security/landlock/syscalls.c
@@ -129,7 +129,7 @@ static const struct file_operations ruleset_fops = {
  	.write = fop_dummy_write,
  };
-#define LANDLOCK_ABI_VERSION 3
+#define LANDLOCK_ABI_VERSION 4
/**
   * sys_landlock_create_ruleset - Create a new ruleset
diff --git a/tools/testing/selftests/landlock/base_test.c b/tools/testing/selftests/landlock/base_test.c
index 72cdae277b02..9f00582f639c 100644
--- a/tools/testing/selftests/landlock/base_test.c
+++ b/tools/testing/selftests/landlock/base_test.c
@@ -75,7 +75,7 @@ TEST(abi_version)
  	const struct landlock_ruleset_attr ruleset_attr = {
  		.handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE,
  	};
-	ASSERT_EQ(3, landlock_create_ruleset(NULL, 0,
+	ASSERT_EQ(4, landlock_create_ruleset(NULL, 0,
  					     LANDLOCK_CREATE_RULESET_VERSION));
ASSERT_EQ(-1, landlock_create_ruleset(&ruleset_attr, 0,
diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index debe2d9ea6cf..f513cd8d9d51 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -404,9 +404,11 @@ TEST_F_FORK(layout1, inval)
  	LANDLOCK_ACCESS_FS_EXECUTE | \
  	LANDLOCK_ACCESS_FS_WRITE_FILE | \
  	LANDLOCK_ACCESS_FS_READ_FILE | \
-	LANDLOCK_ACCESS_FS_TRUNCATE)
+	LANDLOCK_ACCESS_FS_TRUNCATE | \
+	LANDLOCK_ACCESS_FS_CHMOD | \
+	LANDLOCK_ACCESS_FS_CHGRP)
-#define ACCESS_LAST LANDLOCK_ACCESS_FS_TRUNCATE
+#define ACCESS_LAST LANDLOCK_ACCESS_FS_CHGRP
#define ACCESS_ALL ( \
  	ACCESS_FILE | \




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