All of
 help / color / mirror / Atom feed
From: "Günther Noack" <>
Cc: "Mickaël Salaün" <>,
	"James Morris" <>,
	"Paul Moore" <>,
	"Serge E . Hallyn" <>,
	"Günther Noack" <>
Subject: [PATCH v2 0/4] landlock: truncate support
Date: Tue, 12 Jul 2022 23:14:01 +0200	[thread overview]
Message-ID: <> (raw)

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 truncation restriction feature as an
additional bit in the access_mask_t bitmap, in line with the existing
supported operations.

The truncation flag covers both the truncate(2) and ftruncate(2)
families of syscalls, as well as open(2) with the O_TRUNC flag.
This includes uses of creat() that overwrite existing regular files.

Apart from Landlock, file truncation can also be restricted using
seccomp-bpf, but it is more difficult to use (requires BPF, requires
keeping up-to-date syscall lists) and it is not configurable by file
hierarchy, as Landlock is. The simplicity and flexibility of the
Landlock approach makes it worthwhile adding.

While it's possible to use the "write file" and "truncate" rights
independent of each other, it simplifies the mental model for
userspace callers to always use them together.

Specifically, the following behaviours might be surprising for users
when using these independently:

 * The commonly creat() syscall requires the truncate right when
   overwriting existing files, as it is equivalent to open(2) with
 * The "write file" right is not always required to truncate a file,
   even through the open(2) syscall (when using O_RDONLY|O_TRUNC).

Nevertheless, keeping the two flags separate is the correct approach
to guarantee backwards compatibility for existing Landlock users.

These patches are based on version 5.19-rc6.

Best regards,


 * Documentation: Mention the truncation flag where needed.
 * Documentation: Point out connection between truncation and file writing.
 * samples: Add file truncation to the landlock/sandboxer.c sample tool.
 * selftests: Exercise open(2) with O_TRUNC and creat(2) exhaustively.
 * selftests: Exercise truncation syscalls when the truncate right
   is not handled by Landlock.

Previous versions:

Günther Noack (4):
  landlock: Support file truncation
  selftests/landlock: Selftests for file truncation support
  samples/landlock: Extend sample tool to support
  landlock: Document Landlock's file truncation support

 Documentation/userspace-api/landlock.rst     |  24 +-
 include/uapi/linux/landlock.h                |  13 +-
 samples/landlock/sandboxer.c                 |  15 +-
 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   | 245 ++++++++++++++++++-
 8 files changed, 294 insertions(+), 18 deletions(-)


             reply	other threads:[~2022-07-12 21:14 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-07-12 21:14 Günther Noack [this message]
2022-07-12 21:14 ` [PATCH v2 1/4] landlock: Support file truncation Günther Noack
2022-07-28 16:25   ` Mickaël Salaün
2022-07-28 19:02     ` Günther Noack
2022-07-29 10:49   ` Mickaël Salaün
2022-07-31  4:02     ` Günther Noack
2022-07-12 21:14 ` [PATCH v2 2/4] selftests/landlock: Selftests for file truncation support Günther Noack
2022-07-29  9:39   ` Mickaël Salaün
2022-08-04 16:15     ` Günther Noack
2022-07-12 21:14 ` [PATCH v2 3/4] samples/landlock: Extend sample tool to support LANDLOCK_ACCESS_FS_TRUNCATE Günther Noack
2022-07-29 10:31   ` Mickaël Salaün
2022-07-29 10:38     ` Mickaël Salaün
2022-07-29 10:43       ` Mickaël Salaün
2022-08-04 16:34         ` Günther Noack
2022-07-12 21:14 ` [PATCH v2 4/4] landlock: Document Landlock's file truncation support Günther Noack
2022-07-29 10:47   ` Mickaël Salaün
2022-08-04 16:45     ` Günther Noack

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.