linux/security/landlock
Günther Noack b9f5ce27c8
landlock: Support file truncation
Introduce the LANDLOCK_ACCESS_FS_TRUNCATE flag for file truncation.

This flag hooks into the path_truncate, file_truncate and
file_alloc_security LSM hooks and covers file truncation using
truncate(2), ftruncate(2), open(2) with O_TRUNC, as well as creat().

This change also increments the Landlock ABI version, updates
corresponding selftests, and updates code documentation to document
the flag.

In security/security.c, allocate security blobs at pointer-aligned
offsets. This fixes the problem where one LSM's security blob can
shift another LSM's security blob to an unaligned address (reported
by Nathan Chancellor).

The following operations are restricted:

open(2): requires the LANDLOCK_ACCESS_FS_TRUNCATE right if a file gets
implicitly truncated as part of the open() (e.g. using O_TRUNC).

Notable special cases:
* open(..., O_RDONLY|O_TRUNC) can truncate files as well in Linux
* open() with O_TRUNC does *not* need the TRUNCATE right when it
  creates a new file.

truncate(2) (on a path): requires the LANDLOCK_ACCESS_FS_TRUNCATE
right.

ftruncate(2) (on a file): requires that the file had the TRUNCATE
right when it was previously opened. File descriptors acquired by
other means than open(2) (e.g. memfd_create(2)) continue to support
truncation with ftruncate(2).

Cc: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
Acked-by: Paul Moore <paul@paul-moore.com> (LSM)
Link: https://lore.kernel.org/r/20221018182216.301684-5-gnoack3000@gmail.com
Signed-off-by: Mickaël Salaün <mic@digikod.net>
2022-10-19 09:01:44 +02:00
..
common.h landlock: Set up the security framework and manage credentials 2021-04-22 12:22:10 -07:00
cred.c landlock: Format with clang-format 2022-05-09 12:31:10 +02:00
cred.h landlock: Format with clang-format 2022-05-09 12:31:10 +02:00
fs.c landlock: Support file truncation 2022-10-19 09:01:44 +02:00
fs.h landlock: Support file truncation 2022-10-19 09:01:44 +02:00
Kconfig landlock: Support filesystem access-control 2021-04-22 12:22:11 -07:00
limits.h landlock: Support file truncation 2022-10-19 09:01:44 +02:00
Makefile landlock: Add syscall implementations 2021-04-22 12:22:11 -07:00
object.c landlock: Format with clang-format 2022-05-09 12:31:10 +02:00
object.h landlock: Format with clang-format 2022-05-09 12:31:10 +02:00
ptrace.c landlock: Format with clang-format 2022-05-09 12:31:10 +02:00
ptrace.h landlock: Add ptrace restrictions 2021-04-22 12:22:10 -07:00
ruleset.c landlock: Define access_mask_t to enforce a consistent access mask size 2022-05-23 13:27:55 +02:00
ruleset.h landlock: Fix same-layer rule unions 2022-05-23 13:27:57 +02:00
setup.c landlock: Support file truncation 2022-10-19 09:01:44 +02:00
setup.h landlock: Support filesystem access-control 2021-04-22 12:22:11 -07:00
syscalls.c landlock: Support file truncation 2022-10-19 09:01:44 +02:00