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[87.106.108.193]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43fe4e3a18csm55085919f8f.20.2026.04.22.14.36.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Apr 2026 14:36:53 -0700 (PDT) Date: Wed, 22 Apr 2026 23:36:51 +0200 From: =?iso-8859-1?Q?G=FCnther?= Noack To: =?iso-8859-1?Q?Micka=EBl_Sala=FCn?= Cc: Christian Brauner , =?iso-8859-1?Q?G=FCnther?= Noack , Paul Moore , "Serge E . Hallyn" , Justin Suess , Lennart Poettering , Mikhail Ivanov , Nicolas Bouchinet , Shervin Oloumi , Tingmao Wang , kernel-team@cloudflare.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org Subject: Re: [RFC PATCH v1 06/11] landlock: Enforce capability restrictions Message-ID: <20260422.7b9d51611964@gnoack.org> References: <20260312100444.2609563-1-mic@digikod.net> <20260312100444.2609563-7-mic@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: <20260312100444.2609563-7-mic@digikod.net> Hello! On Thu, Mar 12, 2026 at 11:04:39AM +0100, Mickaël Salaün wrote: > diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c > index 152d952e98f6..38a4bf92781a 100644 > --- a/security/landlock/syscalls.c > +++ b/security/landlock/syscalls.c > [...] > + /* > + * Stores only the capabilities this kernel knows about. > + * Unknown bits are silently accepted for forward compatibility: > + * user space compiled against newer headers can pass new > + * CAP_* bits without getting EINVAL on older kernels. > + * Unknown bits have no effect because no hook checks them. > + */ > + mutex_lock(&ruleset->lock); > + ruleset->layers[0].allowed.caps |= > + landlock_caps_to_bits(cap_attr.capabilities & CAP_VALID_MASK); > + mutex_unlock(&ruleset->lock); See the example in the documentation patch set [1]; I think it can be an incompatibility if we ignore the unknown bits here (and I don't know of a scenario where it would be a problem to reject them). [1] https://lore.kernel.org/all/20260422.5a7059c06fb0@gnoack.org/ –Günther