Merge tag 'landlock-6.2-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/mic/linux

Pull landlock updates from Mickaël Salaün:
 "This adds file truncation support to Landlock, contributed by Günther
  Noack. As described by Günther [1], the goal of these patches is to
  work towards a more complete coverage of file system operations that
  are restrictable with Landlock.

  The known set of currently unsupported file system operations in
  Landlock is described at [2]. Out of the operations listed there,
  truncate is the only one that modifies file contents, so these patches
  should make it possible to prevent the direct modification of file
  contents with Landlock.

  The new LANDLOCK_ACCESS_FS_TRUNCATE access right covers both the
  truncate(2) and ftruncate(2) families of syscalls, as well as open(2)
  with the O_TRUNC flag. This includes usages of creat() in the case
  where existing regular files are overwritten.

  Additionally, this introduces a new Landlock security blob associated
  with opened files, to track the available Landlock access rights at
  the time of opening the file. This is in line with Unix's general
  approach of checking the read and write permissions during open(), and
  associating this previously checked authorization with the opened
  file. An ongoing patch documents this use case [3].

  In order to treat truncate(2) and ftruncate(2) calls differently in an
  LSM hook, we split apart the existing security_path_truncate hook into
  security_path_truncate (for truncation by path) and
  security_file_truncate (for truncation of previously opened files)"

Link: https://lore.kernel.org/r/20221018182216.301684-1-gnoack3000@gmail.com [1]
Link: https://www.kernel.org/doc/html/v6.1/userspace-api/landlock.html#filesystem-flags [2]
Link: https://lore.kernel.org/r/20221209193813.972012-1-mic@digikod.net [3]

* tag 'landlock-6.2-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/mic/linux:
  samples/landlock: Document best-effort approach for LANDLOCK_ACCESS_FS_REFER
  landlock: Document Landlock's file truncation support
  samples/landlock: Extend sample tool to support LANDLOCK_ACCESS_FS_TRUNCATE
  selftests/landlock: Test ftruncate on FDs created by memfd_create(2)
  selftests/landlock: Test FD passing from restricted to unrestricted processes
  selftests/landlock: Locally define __maybe_unused
  selftests/landlock: Test open() and ftruncate() in multiple scenarios
  selftests/landlock: Test file truncation support
  landlock: Support file truncation
  landlock: Document init_layer_masks() helper
  landlock: Refactor check_access_path_dual() into is_access_to_paths_allowed()
  security: Create file_truncate hook from path_truncate hook

1 files changed, 9 insertions, 1 deletions

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 1d02d1170e21..dfba3923c76b 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -409,7 +409,9 @@
  *	@attr is the iattr structure containing the new file attributes.
  *	Return 0 if permission is granted.
  * @path_truncate:
- *	Check permission before truncating a file.
+ *	Check permission before truncating the file indicated by path.
+ *	Note that truncation permissions may also be checked based on
+ *	already opened files, using the @file_truncate hook.
  *	@path contains the path structure for the file.
  *	Return 0 if permission is granted.
  * @inode_getattr:
@@ -610,6 +612,12 @@
  *	to receive an open file descriptor via socket IPC.
  *	@file contains the file structure being received.
  *	Return 0 if permission is granted.
+ * @file_truncate:
+ *	Check permission before truncating a file, i.e. using ftruncate.
+ *	Note that truncation permission may also be checked based on the path,
+ *	using the @path_truncate hook.
+ *	@file contains the file structure for the file.
+ *	Return 0 if permission is granted.
  * @file_open:
  *	Save open-time permission checking state for later use upon
  *	file_permission, and recheck access if anything has changed