diff mbox series

[v7,04/18] landlock: move helper functions

Message ID 20220829170401.834298-5-konstantin.meskhidze@huawei.com (mailing list archive)
State Not Applicable
Headers show
Series Network support for Landlock | expand

Checks

Context Check Description
netdev/tree_selection success Not a local patch, async

Commit Message

Konstantin Meskhidze (A) Aug. 29, 2022, 5:03 p.m. UTC
This patch moves unmask_layers() and init_layer_masks() helpers
to ruleset.c to share with landlock network implementation in
following commits.

Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
---

Changes since v6:
* Moves get_handled_accesses() helper from ruleset.c back to fs.c,
  cause it's not used in coming network commits.

Changes since v5:
* Splits commit.
* Moves init_layer_masks() and get_handled_accesses() helpers
to ruleset.c and makes then non-static.
* Formats code with clang-format-14.

---
 security/landlock/fs.c      | 85 -------------------------------------
 security/landlock/ruleset.c | 84 ++++++++++++++++++++++++++++++++++++
 security/landlock/ruleset.h | 10 +++++
 3 files changed, 94 insertions(+), 85 deletions(-)

--
2.25.1

Comments

Mickaël Salaün Sept. 6, 2022, 8:07 a.m. UTC | #1
You can make the subject more informative with "landlock: Move 
unmask_layers() and init_layer_masks()".


On 29/08/2022 19:03, Konstantin Meskhidze wrote:
> This patch moves unmask_layers() and init_layer_masks() helpers
> to ruleset.c to share with landlock network implementation in
> following commits.
> 
> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
> ---
> 
> Changes since v6:
> * Moves get_handled_accesses() helper from ruleset.c back to fs.c,
>    cause it's not used in coming network commits.
> 
> Changes since v5:
> * Splits commit.
> * Moves init_layer_masks() and get_handled_accesses() helpers
> to ruleset.c and makes then non-static.
> * Formats code with clang-format-14.
> 
> ---
>   security/landlock/fs.c      | 85 -------------------------------------
>   security/landlock/ruleset.c | 84 ++++++++++++++++++++++++++++++++++++
>   security/landlock/ruleset.h | 10 +++++
>   3 files changed, 94 insertions(+), 85 deletions(-)
> 
> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> index cca87fcd222d..b03d6153f628 100644
> --- a/security/landlock/fs.c
> +++ b/security/landlock/fs.c
> @@ -215,60 +215,6 @@ find_rule(const struct landlock_ruleset *const domain,
>   	return rule;
>   }
> 
> -/*
> - * @layer_masks is read and may be updated according to the access request and
> - * the matching rule.
> - *
> - * Returns true if the request is allowed (i.e. relevant layer masks for the
> - * request are empty).
> - */
> -static inline bool
> -unmask_layers(const struct landlock_rule *const rule,
> -	      const access_mask_t access_request,
> -	      layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
> -{
> -	size_t layer_level;
> -
> -	if (!access_request || !layer_masks)
> -		return true;
> -	if (!rule)
> -		return false;
> -
> -	/*
> -	 * An access is granted if, for each policy layer, at least one rule
> -	 * encountered on the pathwalk grants the requested access,
> -	 * regardless of its position in the layer stack.  We must then check
> -	 * the remaining layers for each inode, from the first added layer to
> -	 * the last one.  When there is multiple requested accesses, for each
> -	 * policy layer, the full set of requested accesses may not be granted
> -	 * by only one rule, but by the union (binary OR) of multiple rules.
> -	 * E.g. /a/b <execute> + /a <read> => /a/b <execute + read>
> -	 */
> -	for (layer_level = 0; layer_level < rule->num_layers; layer_level++) {
> -		const struct landlock_layer *const layer =
> -			&rule->layers[layer_level];
> -		const layer_mask_t layer_bit = BIT_ULL(layer->level - 1);
> -		const unsigned long access_req = access_request;
> -		unsigned long access_bit;
> -		bool is_empty;
> -
> -		/*
> -		 * Records in @layer_masks which layer grants access to each
> -		 * requested access.
> -		 */
> -		is_empty = true;
> -		for_each_set_bit(access_bit, &access_req,
> -				 ARRAY_SIZE(*layer_masks)) {
> -			if (layer->access & BIT_ULL(access_bit))
> -				(*layer_masks)[access_bit] &= ~layer_bit;
> -			is_empty = is_empty && !(*layer_masks)[access_bit];
> -		}
> -		if (is_empty)
> -			return true;
> -	}
> -	return false;
> -}
> -
>   /*
>    * Allows access to pseudo filesystems that will never be mountable (e.g.
>    * sockfs, pipefs), but can still be reachable through
> @@ -303,37 +249,6 @@ get_handled_accesses(const struct landlock_ruleset *const domain)
>   	return access_dom;
>   }
> 
> -static inline access_mask_t
> -init_layer_masks(const struct landlock_ruleset *const domain,
> -		 const access_mask_t access_request,
> -		 layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
> -{
> -	access_mask_t handled_accesses = 0;
> -	size_t layer_level;
> -
> -	memset(layer_masks, 0, sizeof(*layer_masks));
> -	/* An empty access request can happen because of O_WRONLY | O_RDWR. */
> -	if (!access_request)
> -		return 0;
> -
> -	/* Saves all handled accesses per layer. */
> -	for (layer_level = 0; layer_level < domain->num_layers; layer_level++) {
> -		const unsigned long access_req = access_request;
> -		unsigned long access_bit;
> -
> -		for_each_set_bit(access_bit, &access_req,
> -				 ARRAY_SIZE(*layer_masks)) {
> -			if (landlock_get_fs_access_mask(domain, layer_level) &
> -			    BIT_ULL(access_bit)) {
> -				(*layer_masks)[access_bit] |=
> -					BIT_ULL(layer_level);
> -				handled_accesses |= BIT_ULL(access_bit);
> -			}
> -		}
> -	}
> -	return handled_accesses;
> -}
> -
>   /*
>    * Check that a destination file hierarchy has more restrictions than a source
>    * file hierarchy.  This is only used for link and rename actions.
> diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
> index 3a5ef356aaa3..671a95e2a345 100644
> --- a/security/landlock/ruleset.c
> +++ b/security/landlock/ruleset.c
> @@ -564,3 +564,87 @@ landlock_find_rule(const struct landlock_ruleset *const ruleset,
>   	}
>   	return NULL;
>   }
> +
> +/*
> + * @layer_masks is read and may be updated according to the access request and
> + * the matching rule.
> + *
> + * Returns true if the request is allowed (i.e. relevant layer masks for the
> + * request are empty).
> + */
> +bool unmask_layers(const struct landlock_rule *const rule,
> +		   const access_mask_t access_request,
> +		   layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
> +{
> +	size_t layer_level;
> +
> +	if (!access_request || !layer_masks)
> +		return true;
> +	if (!rule)
> +		return false;
> +
> +	/*
> +	 * An access is granted if, for each policy layer, at least one rule
> +	 * encountered on the pathwalk grants the requested access,
> +	 * regardless of its position in the layer stack.  We must then check
> +	 * the remaining layers for each inode, from the first added layer to
> +	 * the last one.  When there is multiple requested accesses, for each
> +	 * policy layer, the full set of requested accesses may not be granted
> +	 * by only one rule, but by the union (binary OR) of multiple rules.
> +	 * E.g. /a/b <execute> + /a <read> => /a/b <execute + read>
> +	 */
> +	for (layer_level = 0; layer_level < rule->num_layers; layer_level++) {
> +		const struct landlock_layer *const layer =
> +			&rule->layers[layer_level];
> +		const layer_mask_t layer_bit = BIT_ULL(layer->level - 1);
> +		const unsigned long access_req = access_request;
> +		unsigned long access_bit;
> +		bool is_empty;
> +
> +		/*
> +		 * Records in @layer_masks which layer grants access to each
> +		 * requested access.
> +		 */
> +		is_empty = true;
> +		for_each_set_bit(access_bit, &access_req,
> +				 ARRAY_SIZE(*layer_masks)) {
> +			if (layer->access & BIT_ULL(access_bit))
> +				(*layer_masks)[access_bit] &= ~layer_bit;
> +			is_empty = is_empty && !(*layer_masks)[access_bit];
> +		}
> +		if (is_empty)
> +			return true;
> +	}
> +	return false;
> +}
> +
> +access_mask_t
> +init_layer_masks(const struct landlock_ruleset *const domain,
> +		 const access_mask_t access_request,
> +		 layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
> +{
> +	access_mask_t handled_accesses = 0;
> +	size_t layer_level;
> +
> +	memset(layer_masks, 0, sizeof(*layer_masks));
> +	/* An empty access request can happen because of O_WRONLY | O_RDWR. */
> +	if (!access_request)
> +		return 0;
> +
> +	/* Saves all handled accesses per layer. */
> +	for (layer_level = 0; layer_level < domain->num_layers; layer_level++) {
> +		const unsigned long access_req = access_request;
> +		unsigned long access_bit;
> +
> +		for_each_set_bit(access_bit, &access_req,
> +				 ARRAY_SIZE(*layer_masks)) {
> +			if (landlock_get_fs_access_mask(domain, layer_level) &
> +			    BIT_ULL(access_bit)) {
> +				(*layer_masks)[access_bit] |=
> +					BIT_ULL(layer_level);
> +				handled_accesses |= BIT_ULL(access_bit);
> +			}
> +		}
> +	}
> +	return handled_accesses;
> +}
> diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
> index bb1408cc8dd2..d7d9b987829c 100644
> --- a/security/landlock/ruleset.h
> +++ b/security/landlock/ruleset.h
> @@ -235,4 +235,14 @@ landlock_get_fs_access_mask(const struct landlock_ruleset *const ruleset,
>   		LANDLOCK_SHIFT_ACCESS_FS) &
>   	       LANDLOCK_MASK_ACCESS_FS;
>   }
> +
> +bool unmask_layers(const struct landlock_rule *const rule,
> +		   const access_mask_t access_request,
> +		   layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS]);
> +
> +access_mask_t
> +init_layer_masks(const struct landlock_ruleset *const domain,
> +		 const access_mask_t access_request,
> +		 layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS]);
> +
>   #endif /* _SECURITY_LANDLOCK_RULESET_H */
> --
> 2.25.1
>
Konstantin Meskhidze (A) Sept. 10, 2022, 4:50 p.m. UTC | #2
9/6/2022 11:07 AM, Mickaël Salaün пишет:
> You can make the subject more informative with "landlock: Move
> unmask_layers() and init_layer_masks()".
> 
  Ok. Thanks.
> 
> On 29/08/2022 19:03, Konstantin Meskhidze wrote:
>> This patch moves unmask_layers() and init_layer_masks() helpers
>> to ruleset.c to share with landlock network implementation in
>> following commits.
>> 
>> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
>> ---
>> 
>> Changes since v6:
>> * Moves get_handled_accesses() helper from ruleset.c back to fs.c,
>>    cause it's not used in coming network commits.
>> 
>> Changes since v5:
>> * Splits commit.
>> * Moves init_layer_masks() and get_handled_accesses() helpers
>> to ruleset.c and makes then non-static.
>> * Formats code with clang-format-14.
>> 
>> ---
>>   security/landlock/fs.c      | 85 -------------------------------------
>>   security/landlock/ruleset.c | 84 ++++++++++++++++++++++++++++++++++++
>>   security/landlock/ruleset.h | 10 +++++
>>   3 files changed, 94 insertions(+), 85 deletions(-)
>> 
>> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
>> index cca87fcd222d..b03d6153f628 100644
>> --- a/security/landlock/fs.c
>> +++ b/security/landlock/fs.c
>> @@ -215,60 +215,6 @@ find_rule(const struct landlock_ruleset *const domain,
>>   	return rule;
>>   }
>> 
>> -/*
>> - * @layer_masks is read and may be updated according to the access request and
>> - * the matching rule.
>> - *
>> - * Returns true if the request is allowed (i.e. relevant layer masks for the
>> - * request are empty).
>> - */
>> -static inline bool
>> -unmask_layers(const struct landlock_rule *const rule,
>> -	      const access_mask_t access_request,
>> -	      layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
>> -{
>> -	size_t layer_level;
>> -
>> -	if (!access_request || !layer_masks)
>> -		return true;
>> -	if (!rule)
>> -		return false;
>> -
>> -	/*
>> -	 * An access is granted if, for each policy layer, at least one rule
>> -	 * encountered on the pathwalk grants the requested access,
>> -	 * regardless of its position in the layer stack.  We must then check
>> -	 * the remaining layers for each inode, from the first added layer to
>> -	 * the last one.  When there is multiple requested accesses, for each
>> -	 * policy layer, the full set of requested accesses may not be granted
>> -	 * by only one rule, but by the union (binary OR) of multiple rules.
>> -	 * E.g. /a/b <execute> + /a <read> => /a/b <execute + read>
>> -	 */
>> -	for (layer_level = 0; layer_level < rule->num_layers; layer_level++) {
>> -		const struct landlock_layer *const layer =
>> -			&rule->layers[layer_level];
>> -		const layer_mask_t layer_bit = BIT_ULL(layer->level - 1);
>> -		const unsigned long access_req = access_request;
>> -		unsigned long access_bit;
>> -		bool is_empty;
>> -
>> -		/*
>> -		 * Records in @layer_masks which layer grants access to each
>> -		 * requested access.
>> -		 */
>> -		is_empty = true;
>> -		for_each_set_bit(access_bit, &access_req,
>> -				 ARRAY_SIZE(*layer_masks)) {
>> -			if (layer->access & BIT_ULL(access_bit))
>> -				(*layer_masks)[access_bit] &= ~layer_bit;
>> -			is_empty = is_empty && !(*layer_masks)[access_bit];
>> -		}
>> -		if (is_empty)
>> -			return true;
>> -	}
>> -	return false;
>> -}
>> -
>>   /*
>>    * Allows access to pseudo filesystems that will never be mountable (e.g.
>>    * sockfs, pipefs), but can still be reachable through
>> @@ -303,37 +249,6 @@ get_handled_accesses(const struct landlock_ruleset *const domain)
>>   	return access_dom;
>>   }
>> 
>> -static inline access_mask_t
>> -init_layer_masks(const struct landlock_ruleset *const domain,
>> -		 const access_mask_t access_request,
>> -		 layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
>> -{
>> -	access_mask_t handled_accesses = 0;
>> -	size_t layer_level;
>> -
>> -	memset(layer_masks, 0, sizeof(*layer_masks));
>> -	/* An empty access request can happen because of O_WRONLY | O_RDWR. */
>> -	if (!access_request)
>> -		return 0;
>> -
>> -	/* Saves all handled accesses per layer. */
>> -	for (layer_level = 0; layer_level < domain->num_layers; layer_level++) {
>> -		const unsigned long access_req = access_request;
>> -		unsigned long access_bit;
>> -
>> -		for_each_set_bit(access_bit, &access_req,
>> -				 ARRAY_SIZE(*layer_masks)) {
>> -			if (landlock_get_fs_access_mask(domain, layer_level) &
>> -			    BIT_ULL(access_bit)) {
>> -				(*layer_masks)[access_bit] |=
>> -					BIT_ULL(layer_level);
>> -				handled_accesses |= BIT_ULL(access_bit);
>> -			}
>> -		}
>> -	}
>> -	return handled_accesses;
>> -}
>> -
>>   /*
>>    * Check that a destination file hierarchy has more restrictions than a source
>>    * file hierarchy.  This is only used for link and rename actions.
>> diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
>> index 3a5ef356aaa3..671a95e2a345 100644
>> --- a/security/landlock/ruleset.c
>> +++ b/security/landlock/ruleset.c
>> @@ -564,3 +564,87 @@ landlock_find_rule(const struct landlock_ruleset *const ruleset,
>>   	}
>>   	return NULL;
>>   }
>> +
>> +/*
>> + * @layer_masks is read and may be updated according to the access request and
>> + * the matching rule.
>> + *
>> + * Returns true if the request is allowed (i.e. relevant layer masks for the
>> + * request are empty).
>> + */
>> +bool unmask_layers(const struct landlock_rule *const rule,
>> +		   const access_mask_t access_request,
>> +		   layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
>> +{
>> +	size_t layer_level;
>> +
>> +	if (!access_request || !layer_masks)
>> +		return true;
>> +	if (!rule)
>> +		return false;
>> +
>> +	/*
>> +	 * An access is granted if, for each policy layer, at least one rule
>> +	 * encountered on the pathwalk grants the requested access,
>> +	 * regardless of its position in the layer stack.  We must then check
>> +	 * the remaining layers for each inode, from the first added layer to
>> +	 * the last one.  When there is multiple requested accesses, for each
>> +	 * policy layer, the full set of requested accesses may not be granted
>> +	 * by only one rule, but by the union (binary OR) of multiple rules.
>> +	 * E.g. /a/b <execute> + /a <read> => /a/b <execute + read>
>> +	 */
>> +	for (layer_level = 0; layer_level < rule->num_layers; layer_level++) {
>> +		const struct landlock_layer *const layer =
>> +			&rule->layers[layer_level];
>> +		const layer_mask_t layer_bit = BIT_ULL(layer->level - 1);
>> +		const unsigned long access_req = access_request;
>> +		unsigned long access_bit;
>> +		bool is_empty;
>> +
>> +		/*
>> +		 * Records in @layer_masks which layer grants access to each
>> +		 * requested access.
>> +		 */
>> +		is_empty = true;
>> +		for_each_set_bit(access_bit, &access_req,
>> +				 ARRAY_SIZE(*layer_masks)) {
>> +			if (layer->access & BIT_ULL(access_bit))
>> +				(*layer_masks)[access_bit] &= ~layer_bit;
>> +			is_empty = is_empty && !(*layer_masks)[access_bit];
>> +		}
>> +		if (is_empty)
>> +			return true;
>> +	}
>> +	return false;
>> +}
>> +
>> +access_mask_t
>> +init_layer_masks(const struct landlock_ruleset *const domain,
>> +		 const access_mask_t access_request,
>> +		 layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
>> +{
>> +	access_mask_t handled_accesses = 0;
>> +	size_t layer_level;
>> +
>> +	memset(layer_masks, 0, sizeof(*layer_masks));
>> +	/* An empty access request can happen because of O_WRONLY | O_RDWR. */
>> +	if (!access_request)
>> +		return 0;
>> +
>> +	/* Saves all handled accesses per layer. */
>> +	for (layer_level = 0; layer_level < domain->num_layers; layer_level++) {
>> +		const unsigned long access_req = access_request;
>> +		unsigned long access_bit;
>> +
>> +		for_each_set_bit(access_bit, &access_req,
>> +				 ARRAY_SIZE(*layer_masks)) {
>> +			if (landlock_get_fs_access_mask(domain, layer_level) &
>> +			    BIT_ULL(access_bit)) {
>> +				(*layer_masks)[access_bit] |=
>> +					BIT_ULL(layer_level);
>> +				handled_accesses |= BIT_ULL(access_bit);
>> +			}
>> +		}
>> +	}
>> +	return handled_accesses;
>> +}
>> diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
>> index bb1408cc8dd2..d7d9b987829c 100644
>> --- a/security/landlock/ruleset.h
>> +++ b/security/landlock/ruleset.h
>> @@ -235,4 +235,14 @@ landlock_get_fs_access_mask(const struct landlock_ruleset *const ruleset,
>>   		LANDLOCK_SHIFT_ACCESS_FS) &
>>   	       LANDLOCK_MASK_ACCESS_FS;
>>   }
>> +
>> +bool unmask_layers(const struct landlock_rule *const rule,
>> +		   const access_mask_t access_request,
>> +		   layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS]);
>> +
>> +access_mask_t
>> +init_layer_masks(const struct landlock_ruleset *const domain,
>> +		 const access_mask_t access_request,
>> +		 layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS]);
>> +
>>   #endif /* _SECURITY_LANDLOCK_RULESET_H */
>> --
>> 2.25.1
>> 
> .
diff mbox series

Patch

diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index cca87fcd222d..b03d6153f628 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -215,60 +215,6 @@  find_rule(const struct landlock_ruleset *const domain,
 	return rule;
 }

-/*
- * @layer_masks is read and may be updated according to the access request and
- * the matching rule.
- *
- * Returns true if the request is allowed (i.e. relevant layer masks for the
- * request are empty).
- */
-static inline bool
-unmask_layers(const struct landlock_rule *const rule,
-	      const access_mask_t access_request,
-	      layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
-{
-	size_t layer_level;
-
-	if (!access_request || !layer_masks)
-		return true;
-	if (!rule)
-		return false;
-
-	/*
-	 * An access is granted if, for each policy layer, at least one rule
-	 * encountered on the pathwalk grants the requested access,
-	 * regardless of its position in the layer stack.  We must then check
-	 * the remaining layers for each inode, from the first added layer to
-	 * the last one.  When there is multiple requested accesses, for each
-	 * policy layer, the full set of requested accesses may not be granted
-	 * by only one rule, but by the union (binary OR) of multiple rules.
-	 * E.g. /a/b <execute> + /a <read> => /a/b <execute + read>
-	 */
-	for (layer_level = 0; layer_level < rule->num_layers; layer_level++) {
-		const struct landlock_layer *const layer =
-			&rule->layers[layer_level];
-		const layer_mask_t layer_bit = BIT_ULL(layer->level - 1);
-		const unsigned long access_req = access_request;
-		unsigned long access_bit;
-		bool is_empty;
-
-		/*
-		 * Records in @layer_masks which layer grants access to each
-		 * requested access.
-		 */
-		is_empty = true;
-		for_each_set_bit(access_bit, &access_req,
-				 ARRAY_SIZE(*layer_masks)) {
-			if (layer->access & BIT_ULL(access_bit))
-				(*layer_masks)[access_bit] &= ~layer_bit;
-			is_empty = is_empty && !(*layer_masks)[access_bit];
-		}
-		if (is_empty)
-			return true;
-	}
-	return false;
-}
-
 /*
  * Allows access to pseudo filesystems that will never be mountable (e.g.
  * sockfs, pipefs), but can still be reachable through
@@ -303,37 +249,6 @@  get_handled_accesses(const struct landlock_ruleset *const domain)
 	return access_dom;
 }

-static inline access_mask_t
-init_layer_masks(const struct landlock_ruleset *const domain,
-		 const access_mask_t access_request,
-		 layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
-{
-	access_mask_t handled_accesses = 0;
-	size_t layer_level;
-
-	memset(layer_masks, 0, sizeof(*layer_masks));
-	/* An empty access request can happen because of O_WRONLY | O_RDWR. */
-	if (!access_request)
-		return 0;
-
-	/* Saves all handled accesses per layer. */
-	for (layer_level = 0; layer_level < domain->num_layers; layer_level++) {
-		const unsigned long access_req = access_request;
-		unsigned long access_bit;
-
-		for_each_set_bit(access_bit, &access_req,
-				 ARRAY_SIZE(*layer_masks)) {
-			if (landlock_get_fs_access_mask(domain, layer_level) &
-			    BIT_ULL(access_bit)) {
-				(*layer_masks)[access_bit] |=
-					BIT_ULL(layer_level);
-				handled_accesses |= BIT_ULL(access_bit);
-			}
-		}
-	}
-	return handled_accesses;
-}
-
 /*
  * Check that a destination file hierarchy has more restrictions than a source
  * file hierarchy.  This is only used for link and rename actions.
diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index 3a5ef356aaa3..671a95e2a345 100644
--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c
@@ -564,3 +564,87 @@  landlock_find_rule(const struct landlock_ruleset *const ruleset,
 	}
 	return NULL;
 }
+
+/*
+ * @layer_masks is read and may be updated according to the access request and
+ * the matching rule.
+ *
+ * Returns true if the request is allowed (i.e. relevant layer masks for the
+ * request are empty).
+ */
+bool unmask_layers(const struct landlock_rule *const rule,
+		   const access_mask_t access_request,
+		   layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
+{
+	size_t layer_level;
+
+	if (!access_request || !layer_masks)
+		return true;
+	if (!rule)
+		return false;
+
+	/*
+	 * An access is granted if, for each policy layer, at least one rule
+	 * encountered on the pathwalk grants the requested access,
+	 * regardless of its position in the layer stack.  We must then check
+	 * the remaining layers for each inode, from the first added layer to
+	 * the last one.  When there is multiple requested accesses, for each
+	 * policy layer, the full set of requested accesses may not be granted
+	 * by only one rule, but by the union (binary OR) of multiple rules.
+	 * E.g. /a/b <execute> + /a <read> => /a/b <execute + read>
+	 */
+	for (layer_level = 0; layer_level < rule->num_layers; layer_level++) {
+		const struct landlock_layer *const layer =
+			&rule->layers[layer_level];
+		const layer_mask_t layer_bit = BIT_ULL(layer->level - 1);
+		const unsigned long access_req = access_request;
+		unsigned long access_bit;
+		bool is_empty;
+
+		/*
+		 * Records in @layer_masks which layer grants access to each
+		 * requested access.
+		 */
+		is_empty = true;
+		for_each_set_bit(access_bit, &access_req,
+				 ARRAY_SIZE(*layer_masks)) {
+			if (layer->access & BIT_ULL(access_bit))
+				(*layer_masks)[access_bit] &= ~layer_bit;
+			is_empty = is_empty && !(*layer_masks)[access_bit];
+		}
+		if (is_empty)
+			return true;
+	}
+	return false;
+}
+
+access_mask_t
+init_layer_masks(const struct landlock_ruleset *const domain,
+		 const access_mask_t access_request,
+		 layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
+{
+	access_mask_t handled_accesses = 0;
+	size_t layer_level;
+
+	memset(layer_masks, 0, sizeof(*layer_masks));
+	/* An empty access request can happen because of O_WRONLY | O_RDWR. */
+	if (!access_request)
+		return 0;
+
+	/* Saves all handled accesses per layer. */
+	for (layer_level = 0; layer_level < domain->num_layers; layer_level++) {
+		const unsigned long access_req = access_request;
+		unsigned long access_bit;
+
+		for_each_set_bit(access_bit, &access_req,
+				 ARRAY_SIZE(*layer_masks)) {
+			if (landlock_get_fs_access_mask(domain, layer_level) &
+			    BIT_ULL(access_bit)) {
+				(*layer_masks)[access_bit] |=
+					BIT_ULL(layer_level);
+				handled_accesses |= BIT_ULL(access_bit);
+			}
+		}
+	}
+	return handled_accesses;
+}
diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
index bb1408cc8dd2..d7d9b987829c 100644
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h
@@ -235,4 +235,14 @@  landlock_get_fs_access_mask(const struct landlock_ruleset *const ruleset,
 		LANDLOCK_SHIFT_ACCESS_FS) &
 	       LANDLOCK_MASK_ACCESS_FS;
 }
+
+bool unmask_layers(const struct landlock_rule *const rule,
+		   const access_mask_t access_request,
+		   layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS]);
+
+access_mask_t
+init_layer_masks(const struct landlock_ruleset *const domain,
+		 const access_mask_t access_request,
+		 layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS]);
+
 #endif /* _SECURITY_LANDLOCK_RULESET_H */