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Hallyn" Subject: Re: [PATCH v3 1/4] landlock: Support file truncation Message-ID: References: <20220804193746.9161-1-gnoack3000@gmail.com> <20220804193746.9161-2-gnoack3000@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: On Thu, Aug 11, 2022 at 06:59:28PM +0200, Mickaël Salaün wrote: > > On 04/08/2022 21:37, Günther Noack wrote: > > Introduce the LANDLOCK_ACCESS_FS_TRUNCATE flag for file truncation. > > > > This flag hooks into the path_truncate LSM hook 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 includes minor documentation changes to > > document the flag. > > > > Signed-off-by: Günther Noack > > --- > > Documentation/userspace-api/landlock.rst | 6 ++++++ > > include/uapi/linux/landlock.h | 17 ++++++++++++----- > > 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 | 7 ++++--- > > 7 files changed, 33 insertions(+), 12 deletions(-) > > > > diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst > > index b8ea59493964..d92e335380d4 100644 > > --- a/Documentation/userspace-api/landlock.rst > > +++ b/Documentation/userspace-api/landlock.rst > > @@ -380,6 +380,12 @@ by the Documentation/admin-guide/cgroup-v1/memory.rst. > > Previous limitations > > ==================== > > +File truncation (ABI < 3) > > +------------------------- > > + > > +File truncation could not be denied before the third Landlock ABI, so it is > > +always allowed when using a kernel that only supports the first or second ABI. > > I think this addition could make the documentation more consistent and > helpful: > > Starting with the Landlock ABI version 3, it is now possible to securely > control truncation thanks to the new `LANDLOCK_ACCESS_FS_TRUNCATE` > access right. Agreed, I added that sentence. > > > > + > > File renaming and linking (ABI 1) > > --------------------------------- > > diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h > > index 23df4e0e8ace..1beb8289708d 100644 > > --- a/include/uapi/linux/landlock.h > > +++ b/include/uapi/linux/landlock.h > > @@ -95,8 +95,15 @@ struct landlock_path_beneath_attr { > > * A file can only receive these access rights: > > * > > * - %LANDLOCK_ACCESS_FS_EXECUTE: Execute a file. > > - * - %LANDLOCK_ACCESS_FS_WRITE_FILE: Open a file with write access. > > + * - %LANDLOCK_ACCESS_FS_WRITE_FILE: Open a file with write access. Note that > > + * you might additionally need the LANDLOCK_ACCESS_FS_TRUNCATE right in order > > Please use backquotes for code such as `LANDLOCK_ACCESS_FS_TRUNCATE`, > `O_TRUNC`… Done. > > > > + * to overwrite files with :manpage:`open(2)` using O_TRUNC or > > + * :manpage:`creat(2)`. > > * - %LANDLOCK_ACCESS_FS_READ_FILE: Open a file with read access. > > + * - %LANDLOCK_ACCESS_FS_TRUNCATE: Truncate a file through file truncation APIs > > + * like :manpage:`truncate(2)`, :manpage:`ftruncate(2)`, or > > + * :manpage:`open(2)` with O_TRUNC or :manpage:`creat(2)`. This access right > > + * is available since the third version of the Landlock ABI. > > * > > * A directory can receive access rights related to files or directories. The > > * following access right is applied to the directory itself, and the > > @@ -139,10 +146,9 @@ struct landlock_path_beneath_attr { > > * > > * It is currently not possible to restrict some file-related actions > > * accessible through these syscall families: :manpage:`chdir(2)`, > > - * :manpage:`truncate(2)`, :manpage:`stat(2)`, :manpage:`flock(2)`, > > - * :manpage:`chmod(2)`, :manpage:`chown(2)`, :manpage:`setxattr(2)`, > > - * :manpage:`utime(2)`, :manpage:`ioctl(2)`, :manpage:`fcntl(2)`, > > - * :manpage:`access(2)`. > > + * :manpage:`stat(2)`, :manpage:`flock(2)`, :manpage:`chmod(2)`, > > + * :manpage:`chown(2)`, :manpage:`setxattr(2)`, :manpage:`utime(2)`, > > + * :manpage:`ioctl(2)`, :manpage:`fcntl(2)`, :manpage:`access(2)`. > > * Future Landlock evolutions will enable to restrict them. > > */ > > /* clang-format off */ --