On Tue, Oct 18, 2022 at 2:22 PM Günther Noack <gnoack3000@xxxxxxxxx> wrote: > > 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). > > Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx> > Signed-off-by: Günther Noack <gnoack3000@xxxxxxxxx> > --- > include/uapi/linux/landlock.h | 21 +++- > security/landlock/fs.c | 104 ++++++++++++++++++- > security/landlock/fs.h | 24 +++++ > security/landlock/limits.h | 2 +- > security/landlock/setup.c | 1 + > security/landlock/syscalls.c | 2 +- > security/security.c | 11 +- > tools/testing/selftests/landlock/base_test.c | 2 +- > tools/testing/selftests/landlock/fs_test.c | 7 +- > 9 files changed, 153 insertions(+), 21 deletions(-) Thanks for the LSM security blob allocator fixes Günther! Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx> (LSM) -- paul-moore.com
