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Tue, 24 Mar 2026 02:48:34 -0700 (PDT) Date: Tue, 24 Mar 2026 10:48:29 +0100 From: =?utf-8?Q?G=C3=BCnther?= Noack To: =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= Cc: "Panagiotis \"Ivory\" Vasilopoulos" , Jonathan Corbet , Shuah Khan , linux-security-module@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Dan Cojocaru Subject: Re: [PATCH v4] landlock: Expand restrict flags example for ABI version 8 Message-ID: References: <20260304-landlock-docs-add-tsync-example-v4-1-819a276f05c5@n0toose.net> <20260323.sheiHaR5uRoo@digikod.net> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260323.sheiHaR5uRoo@digikod.net> Hello! On Mon, Mar 23, 2026 at 07:56:21PM +0100, Mickaël Salaün wrote: > Thanks! I pushed your patch in next with a minor fix. > > Günther, does it look good to you? > > On Wed, Mar 04, 2026 at 07:13:04PM +0100, Panagiotis "Ivory" Vasilopoulos wrote: > > Add LANDLOCK_RESTRICT_SELF_TSYNC to the backwards compatibility example > > for restrict flags. This introduces completeness, similar to that of > > the ruleset attributes example. However, as the new example can impact > > enforcement in certain cases, an appropriate warning is also included. > > > > Additionally, I modified the two comments of the example to make them > > more consistent with the ruleset attributes example's. > > > > Signed-off-by: Panagiotis 'Ivory' Vasilopoulos > > Co-developed-by: Dan Cojocaru > > Signed-off-by: Dan Cojocaru > > --- > > Changes in v4: > > - Make warning somewhat more terse, merge comments. > > - Remove some sensationalization. ("Don't copy-paste this just yet!") > > - Apply Günther's suggestion (v3 "recycled" some phrases, was long) > > - ... but also retain some of the wording on ABI differences > > - Provide a brief overview that contextualizes the example further: > > - Clarify the difference behind ABI < 8 & ABI v8, to avoid > > misunderstandings on which option is the default. > > - Make "linear reading" easier. > > - Based on Mickaël's feedback: Avoid cans of worms w.r.t. use cases > > - Link to v3: https://lore.kernel.org/r/20260228-landlock-docs-add-tsync-example-v3-1-140ab50f0524@n0toose.net > > > > Changes in v3: > > - Add __attribute__((fallthrough)) like in earlier example. > > - Improve comment for LANDLOCK_RESTRICT_SELF_TSYNC (ABI < 8) example. > > - Add relevant warning for ABI < 8 example based on Günther's feedback. > > - Link to v2: https://lore.kernel.org/r/20260221-landlock-docs-add-tsync-example-v2-1-60990986bba5@n0toose.net > > > > Changes in v2: > > - Fix formatting error. > > - Link to v1: https://lore.kernel.org/r/20260221-landlock-docs-add-tsync-example-v1-1-f89383809eb4@n0toose.net > > --- > > Documentation/userspace-api/landlock.rst | 22 ++++++++++++++++++---- > > 1 file changed, 18 insertions(+), 4 deletions(-) > > > > diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst > > index 13134bccdd39d78ddce3daf454f32dda162ce91b..64c7138a788d74f99da0a71428da392b3d873bf8 100644 > > --- a/Documentation/userspace-api/landlock.rst > > +++ b/Documentation/userspace-api/landlock.rst > > @@ -196,13 +196,27 @@ similar backwards compatibility check is needed for the restrict flags > > (see sys_landlock_restrict_self() documentation for available flags): > > > > .. code-block:: c > > - > > - __u32 restrict_flags = LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON; > > - if (abi < 7) { > > - /* Clear logging flags unsupported before ABI 7. */ > > + __u32 restrict_flags = > > + LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON | > > + LANDLOCK_RESTRICT_SELF_TSYNC; > > + switch (abi) { > > + case 1 ... 6: > > + /* Clear logging flags unsupported for ABI < 7 */ > > restrict_flags &= ~(LANDLOCK_RESTRICT_SELF_LOG_SAME_EXEC_OFF | > > LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON | > > LANDLOCK_RESTRICT_SELF_LOG_SUBDOMAINS_OFF); > > + __attribute__((fallthrough)); > > + case 7: > > + /* > > + * Removes multithreaded enforcement flag unsupported for ABI < 8 > > + * > > + * WARNING: Without this flag, calling landlock_restrict_self(2) is > > + * only equivalent if the calling process is single-threaded. Below > > + * ABI v8 (and as of ABI v8, when not using this flag), a Landlock > > + * policy would only be enforced for the calling thread and its > > + * children (and not for all threads, including parents and siblings). > > + */ > > + restrict_flags &= ~LANDLOCK_RESTRICT_SELF_TSYNC; > > } > > > > The next step is to restrict the current thread from gaining more privileges > > > > --- > > base-commit: ceb977bfe9e8715e6cd3a4785c7aab8ea5cd2b77 > > change-id: 20260221-landlock-docs-add-tsync-example-e8fd5c64a366 > > > > Best regards, > > -- > > Panagiotis "Ivory" Vasilopoulos > > > > Apologies for the delay, this must have slipped through the cracks. Thanks for bringing it up again. Yes, this looks good. Signed-off-by: Günther Noack —Günther