Re: [PATCH v8 05/12] landlock: Refactor unmask_layers() and init_layer_masks()

["Mickaël Salaün" <mic@digikod.net>]

On 21/10/2022 17:26, Konstantin Meskhidze wrote:
> Adds new key_type argument to init_layer_masks() helper.

Add a new key_type argument to the…

> Adds masks_array_size argument  to unmask_layers() helper.

Add a masks_array_size argument to the…


The name of these helpers need to be prefixed with "landlock_".


> These modifications support implementing new rule types in the next
> Landlock versions.
> 
> Co-developed-by: Mickaël Salaün <mic@digikod.net>

Signed-off-by: Mickaël Salaün <mic@digikod.net>

> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
> ---
> 
> Changes since v7:
> * Refactors commit message, adds a co-developer.
> * Minor fixes.
> 
> Changes since v6:
> * Removes masks_size attribute from init_layer_masks().
> * Refactors init_layer_masks() with new landlock_key_type.
> 
> Changes since v5:
> * Splits commit.
> * Formats code with clang-format-14.
> 
> Changes since v4:
> * Refactors init_layer_masks(), get_handled_accesses()
> and unmask_layers() functions to support multiple rule types.
> * Refactors landlock_get_fs_access_mask() function with
> LANDLOCK_MASK_ACCESS_FS mask.
> 
> Changes since v3:
> * Splits commit.
> * Refactors landlock_unmask_layers functions.
> 
> ---
>   security/landlock/fs.c      | 36 ++++++++++++++++++-------------
>   security/landlock/ruleset.c | 42 ++++++++++++++++++++++++++-----------
>   security/landlock/ruleset.h | 11 +++++-----
>   3 files changed, 58 insertions(+), 31 deletions(-)
> 
> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> index 240e42a8f788..fe76a11483f8 100644
> --- a/security/landlock/fs.c
> +++ b/security/landlock/fs.c
> @@ -435,16 +435,20 @@ static bool is_access_to_paths_allowed(
>   	if (unlikely(dentry_child1)) {
>   		unmask_layers(find_rule(domain, dentry_child1),
>   			      init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS,
> -					       &_layer_masks_child1),
> -			      &_layer_masks_child1);
> +					       &_layer_masks_child1,
> +					       LANDLOCK_KEY_INODE),
> +			      &_layer_masks_child1,
> +			      ARRAY_SIZE(_layer_masks_child1));
>   		layer_masks_child1 = &_layer_masks_child1;
>   		child1_is_directory = d_is_dir(dentry_child1);
>   	}
>   	if (unlikely(dentry_child2)) {
>   		unmask_layers(find_rule(domain, dentry_child2),
>   			      init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS,
> -					       &_layer_masks_child2),
> -			      &_layer_masks_child2);
> +					       &_layer_masks_child2,
> +					       LANDLOCK_KEY_INODE),
> +			      &_layer_masks_child2,
> +			      ARRAY_SIZE(_layer_masks_child2));
>   		layer_masks_child2 = &_layer_masks_child2;
>   		child2_is_directory = d_is_dir(dentry_child2);
>   	}
> @@ -496,15 +500,16 @@ static bool is_access_to_paths_allowed(
>   		}
> 
>   		rule = find_rule(domain, walker_path.dentry);
> -		allowed_parent1 = unmask_layers(rule, access_masked_parent1,
> -						layer_masks_parent1);
> -		allowed_parent2 = unmask_layers(rule, access_masked_parent2,
> -						layer_masks_parent2);
> +		allowed_parent1 = unmask_layers(
> +			rule, access_masked_parent1, layer_masks_parent1,
> +			ARRAY_SIZE(*layer_masks_parent1));
> +		allowed_parent2 = unmask_layers(
> +			rule, access_masked_parent2, layer_masks_parent2,
> +			ARRAY_SIZE(*layer_masks_parent2));
> 
>   		/* Stops when a rule from each layer grants access. */
>   		if (allowed_parent1 && allowed_parent2)
>   			break;
> -
>   jump_up:
>   		if (walker_path.dentry == walker_path.mnt->mnt_root) {
>   			if (follow_up(&walker_path)) {
> @@ -543,7 +548,8 @@ static inline int check_access_path(const struct landlock_ruleset *const domain,
>   {
>   	layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {};
> 
> -	access_request = init_layer_masks(domain, access_request, &layer_masks);
> +	access_request = init_layer_masks(domain, access_request, &layer_masks,
> +					  LANDLOCK_KEY_INODE);
>   	if (is_access_to_paths_allowed(domain, path, access_request,
>   				       &layer_masks, NULL, 0, NULL, NULL))
>   		return 0;
> @@ -630,7 +636,7 @@ static bool collect_domain_accesses(
>   		return true;
> 
>   	access_dom = init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS,
> -				      layer_masks_dom);
> +				      layer_masks_dom, LANDLOCK_KEY_INODE);
> 
>   	dget(dir);
>   	while (true) {
> @@ -638,7 +644,8 @@ static bool collect_domain_accesses(
> 
>   		/* Gets all layers allowing all domain accesses. */
>   		if (unmask_layers(find_rule(domain, dir), access_dom,
> -				  layer_masks_dom)) {
> +				  layer_masks_dom,
> +				  ARRAY_SIZE(*layer_masks_dom))) {
>   			/*
>   			 * Stops when all handled accesses are allowed by at
>   			 * least one rule in each layer.
> @@ -754,7 +761,7 @@ static int current_check_refer_path(struct dentry *const old_dentry,
>   		 */
>   		access_request_parent1 = init_layer_masks(
>   			dom, access_request_parent1 | access_request_parent2,
> -			&layer_masks_parent1);
> +			&layer_masks_parent1, LANDLOCK_KEY_INODE);
>   		if (is_access_to_paths_allowed(
>   			    dom, new_dir, access_request_parent1,
>   			    &layer_masks_parent1, NULL, 0, NULL, NULL))
> @@ -1131,7 +1138,8 @@ static int hook_file_open(struct file *const file)
> 
>   	if (is_access_to_paths_allowed(
>   		    dom, &file->f_path,
> -		    init_layer_masks(dom, full_access_request, &layer_masks),
> +		    init_layer_masks(dom, full_access_request, &layer_masks,
> +				     LANDLOCK_KEY_INODE),
>   		    &layer_masks, NULL, 0, NULL, NULL)) {
>   		allowed_access = full_access_request;
>   	} else {
> diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
> index 02ab14439c43..c7cf54ba4f6d 100644
> --- a/security/landlock/ruleset.c
> +++ b/security/landlock/ruleset.c
> @@ -576,13 +576,15 @@ landlock_find_rule(const struct landlock_ruleset *const ruleset,
>   /*
>    * @layer_masks is read and may be updated according to the access request and
>    * the matching rule.
> + * @masks_array_size must be equal to ARRAY_SIZE(*layer_masks).
>    *
>    * 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])
> +		   layer_mask_t (*const layer_masks)[],
> +		   const size_t masks_array_size)
>   {
>   	size_t layer_level;
> 
> @@ -614,8 +616,7 @@ bool unmask_layers(const struct landlock_rule *const rule,
>   		 * requested access.
>   		 */
>   		is_empty = true;
> -		for_each_set_bit(access_bit, &access_req,
> -				 ARRAY_SIZE(*layer_masks)) {
> +		for_each_set_bit(access_bit, &access_req, masks_array_size) {
>   			if (layer->access & BIT_ULL(access_bit))
>   				(*layer_masks)[access_bit] &= ~layer_bit;
>   			is_empty = is_empty && !(*layer_masks)[access_bit];
> @@ -626,6 +627,10 @@ bool unmask_layers(const struct landlock_rule *const rule,
>   	return false;
>   }
> 
> +typedef access_mask_t
> +get_access_mask_t(const struct landlock_ruleset *const ruleset,
> +		  const u16 layer_level);
> +
>   /**
>    * init_layer_masks - Initialize layer masks from an access request
>    *
> @@ -635,19 +640,33 @@ bool unmask_layers(const struct landlock_rule *const rule,
>    * @domain: The domain that defines the current restrictions.
>    * @access_request: The requested access rights to check.
>    * @layer_masks: The layer masks to populate.
> + * @key_type: The key type to switch between access masks of different types.
>    *
>    * Returns: An access mask where each access right bit is set which is handled
>    * in any of the active layers in @domain.
>    */
> -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 init_layer_masks(const struct landlock_ruleset *const domain,
> +			       const access_mask_t access_request,
> +			       layer_mask_t (*const layer_masks)[],
> +			       const enum landlock_key_type key_type)
>   {
>   	access_mask_t handled_accesses = 0;
> -	size_t layer_level;
> +	size_t layer_level, num_access;
> +	get_access_mask_t *get_access_mask;
> +
> +	switch (key_type) {
> +	case LANDLOCK_KEY_INODE:
> +		get_access_mask = landlock_get_fs_access_mask;
> +		num_access = LANDLOCK_NUM_ACCESS_FS;
> +		break;
> +	default:
> +		WARN_ON_ONCE(1);
> +		return 0;
> +	}
> +
> +	memset(layer_masks, 0,
> +	       array_size(sizeof((*layer_masks)[0]), num_access));
> 
> -	memset(layer_masks, 0, sizeof(*layer_masks));
>   	/* An empty access request can happen because of O_WRONLY | O_RDWR. */
>   	if (!access_request)
>   		return 0;
> @@ -657,14 +676,13 @@ init_layer_masks(const struct landlock_ruleset *const domain,
>   		const unsigned long access_req = access_request;
>   		unsigned long access_bit;
> 
> -		for_each_set_bit(access_bit, &access_req,
> -				 ARRAY_SIZE(*layer_masks)) {
> +		for_each_set_bit(access_bit, &access_req, num_access) {
>   			/*
>   			 * Artificially handles all initially denied by default
>   			 * access rights.
>   			 */
>   			if (BIT_ULL(access_bit) &
> -			    (landlock_get_fs_access_mask(domain, layer_level) |
> +			    (get_access_mask(domain, layer_level) |
>   			     ACCESS_INITIALLY_DENIED)) {
>   				(*layer_masks)[access_bit] |=
>   					BIT_ULL(layer_level);
> diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
> index 50baff4fcbb4..d9eb79ea9a89 100644
> --- a/security/landlock/ruleset.h
> +++ b/security/landlock/ruleset.h
> @@ -259,11 +259,12 @@ landlock_get_fs_access_mask(const struct landlock_ruleset *const ruleset,
> 
>   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]);
> +		   layer_mask_t (*const layer_masks)[],
> +		   const size_t masks_array_size);
> 
> -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 init_layer_masks(const struct landlock_ruleset *const domain,
> +			       const access_mask_t access_request,
> +			       layer_mask_t (*const layer_masks)[],
> +			       const enum landlock_key_type key_type);
> 
>   #endif /* _SECURITY_LANDLOCK_RULESET_H */
> --
> 2.25.1
>