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[87.106.108.193]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-435e132368csm11568529f8f.31.2026.01.28.23.56.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Jan 2026 23:56:42 -0800 (PST) Date: Thu, 29 Jan 2026 08:56:37 +0100 From: =?iso-8859-1?Q?G=FCnther?= Noack To: =?iso-8859-1?Q?Micka=EBl_Sala=FCn?= Cc: linux-security-module@vger.kernel.org, Tingmao Wang , Justin Suess , Samasth Norway Ananda , Matthieu Buffet , Mikhail Ivanov , konstantin.meskhidze@huawei.com, Randy Dunlap Subject: Re: [PATCH v2 3/3] landlock: transpose the layer masks data structure Message-ID: <20260129.691d9b85a887@gnoack.org> References: <20260125195853.109967-1-gnoack3000@gmail.com> <20260125195853.109967-4-gnoack3000@gmail.com> <20260128.quaido7ia0Xu@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: <20260128.quaido7ia0Xu@digikod.net> On Wed, Jan 28, 2026 at 10:34:02PM +0100, Mickaël Salaün wrote: > On Sun, Jan 25, 2026 at 08:58:53PM +0100, Günther Noack wrote: > > Tradeoffs: > > > > This change improves performance, at a slight size increase to the > > layer masks data structure. > > > > At the moment, for the filesystem access rights, the data structure > > has the same size as before, but once we introduce the 17th filesystem > > access right, it will double in size (from 32 to 64 bytes), as > > ...for all access rights (e.g. even if there is no new network one) Added. > > --- a/security/landlock/audit.c > > +++ b/security/landlock/audit.c > > @@ -180,38 +180,21 @@ static void test_get_hierarchy(struct kunit *const test) > > > > #endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */ > > > > +/* get_denied_layer - get the youngest layer that denied the access_request */ > > /* Get the youngest layer that denied the access_request. */ OK, done. I also changed to non-docstring style for the access_mask_subset() helper. > > > static size_t get_denied_layer(const struct landlock_ruleset *const domain, > > access_mask_t *const access_request, > > - const layer_mask_t (*const layer_masks)[], > > - const size_t layer_masks_size) > > + const struct layer_access_masks *masks) > > { > > - const unsigned long access_req = *access_request; > > - unsigned long access_bit; > > - access_mask_t missing = 0; > > - long youngest_layer = -1; > > - > > - for_each_set_bit(access_bit, &access_req, layer_masks_size) { > > - const layer_mask_t mask = (*layer_masks)[access_bit]; > > - long layer; > > - > > - if (!mask) > > - continue; > > - > > - /* __fls(1) == 0 */ > > - layer = __fls(mask); > > - if (layer > youngest_layer) { > > - youngest_layer = layer; > > - missing = BIT(access_bit); > > - } else if (layer == youngest_layer) { > > - missing |= BIT(access_bit); > > + for (int i = ARRAY_SIZE(masks->access) - 1; i >= 0; i--) { > > size_t i This is one of the two places where this didn't work. The loop goes from top to bottom here, and the "i >= 0" check would always be true for a size_t. If there is a more idiomatic way to write that loop, I can switch to it, but would otherwise lean towards keeping it as it is? > > + if (masks->access[i] & *access_request) { > > + *access_request &= masks->access[i]; > > + return i; > > } > > } > > > > - for_each_set_bit(access_bit, &access_opt, layer_masks_size) { > > - const layer_mask_t mask = (*layer_masks)[access_bit]; > > + for (int i = ARRAY_SIZE(masks->access) - 1; i >= 0; i--) { > > size_t i Ditto, the loop goes from top to bottom here. > > + const access_mask_t denied = masks->access[i] & optional_access; > > + const unsigned long newly_denied = denied & ~all_denied; > > > > -static bool > > -scope_to_request(const access_mask_t access_request, > > - layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS]) > > +static bool scope_to_request(const access_mask_t access_request, > > + struct layer_access_masks *masks) > > { > > - const unsigned long access_req = access_request; > > - unsigned long access_bit; > > + bool saw_unfulfilled_access = false; > > > > - if (WARN_ON_ONCE(!layer_masks)) > > + if (WARN_ON_ONCE(!masks)) > > return true; > > > > - for_each_clear_bit(access_bit, &access_req, ARRAY_SIZE(*layer_masks)) > > - (*layer_masks)[access_bit] = 0; > > - > > - return is_layer_masks_allowed(layer_masks); > > + for (size_t i = 0; i < ARRAY_SIZE(masks->access); i++) { > > + masks->access[i] &= access_request; > > + if (masks->access[i]) > > { > > > + saw_unfulfilled_access = true; > > break; > } Two lines above, this loop mutates masks->access[...]: masks->access[i] &= access_request If we break the loop early, we would not actually scope it down to the request entirely? Is this safe? > > + } > > + return !saw_unfulfilled_access; > > } –Günther