[PATCH 0/2] landlock: truncate(2) support

[Günther Noack]

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 [1]. 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 patch introduces the truncate(2) restriction feature as an
additional bit in the access_mask_t bitmap, in line with the existing
supported operations.

Apart from Landlock, the truncate(2) and ftruncate(2) family of system
calls can also be restricted using seccomp-bpf, but it is a
complicated mechanism (requires BPF, requires keeping up-to-date
syscall lists) and it also is not configurable by file hierarchy, as
Landlock is. The simplicity and flexibility of the Landlock approach
makes it worthwhile adding.

I am aware that the documentation and samples/landlock/sandboxer.c
tool still need corresponding updates; I'm hoping to get some early
feedback this way.

These patches are based on version 5.19-rc5.
The patch set can also be browsed on the web at [2].

Best regards,
Günther

[1] https://docs.kernel.org/userspace-api/landlock.html#filesystem-flags
[2] https://github.com/gnoack/linux/tree/landlock-truncate

Günther Noack (2):
  landlock: Support truncate(2).
  landlock: Selftests for truncate(2) support.

 include/uapi/linux/landlock.h                |  2 +
 security/landlock/fs.c                       |  9 +-
 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   | 87 +++++++++++++++++++-
 6 files changed, 97 insertions(+), 7 deletions(-)

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2.37.0