[PATCH v8 3/9] landlock: Refactor check_access_path_dual() into is_access_to_paths_allowed()

[Mickaël Salaün]

Great!

On 01/10/2022 17:49, Günther Noack wrote:
> * Rename it to is_access_to_paths_allowed()
> * Make it return true iff the access is allowed
> * Calculate the EXDEV/EACCES error code in the one place where it's needed

Can you please replace these bullet points with (one-sentence) paragraphs?


> 
> Suggested-by: Mickaël Salaün <mic at digikod.net>
> Signed-off-by: Günther Noack <gnoack3000 at gmail.com>
> ---
>   security/landlock/fs.c | 89 +++++++++++++++++++++---------------------
>   1 file changed, 44 insertions(+), 45 deletions(-)
> 
> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> index a9dbd99d9ee7..083dd3d359de 100644
> --- a/security/landlock/fs.c
> +++ b/security/landlock/fs.c
> @@ -430,7 +430,7 @@ is_eacces(const layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS],
>   }
>   
>   /**
> - * check_access_path_dual - Check accesses for requests with a common path
> + * is_access_to_paths_allowed - Check accesses for requests with a common path
>    *
>    * @domain: Domain to check against.
>    * @path: File hierarchy to walk through.
> @@ -465,14 +465,10 @@ is_eacces(const layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS],
>    * allow the request.
>    *
>    * Returns:
> - * - 0 if the access request is granted;
> - * - -EACCES if it is denied because of access right other than
> - *   LANDLOCK_ACCESS_FS_REFER;
> - * - -EXDEV if the renaming or linking would be a privileged escalation
> - *   (according to each layered policies), or if LANDLOCK_ACCESS_FS_REFER is
> - *   not allowed by the source or the destination.
> + * - true if the access request is granted;
> + * - false otherwise

Missing final dot.


>    */
> -static int check_access_path_dual(
> +static bool is_access_to_paths_allowed(
>   	const struct landlock_ruleset *const domain,
>   	const struct path *const path,
>   	const access_mask_t access_request_parent1,
> @@ -492,17 +488,17 @@ static int check_access_path_dual(
>   	(*layer_masks_child2)[LANDLOCK_NUM_ACCESS_FS] = NULL;
>   
>   	if (!access_request_parent1 && !access_request_parent2)
> -		return 0;
> +		return true;
>   	if (WARN_ON_ONCE(!domain || !path))
> -		return 0;
> +		return true;
>   	if (is_nouser_or_private(path->dentry))
> -		return 0;
> +		return true;
>   	if (WARN_ON_ONCE(domain->num_layers < 1 || !layer_masks_parent1))
> -		return -EACCES;
> +		return false;
>   
>   	if (unlikely(layer_masks_parent2)) {
>   		if (WARN_ON_ONCE(!dentry_child1))
> -			return -EACCES;
> +			return false;
>   		/*
>   		 * For a double request, first check for potential privilege
>   		 * escalation by looking at domain handled accesses (which are
> @@ -513,7 +509,7 @@ static int check_access_path_dual(
>   		is_dom_check = true;
>   	} else {
>   		if (WARN_ON_ONCE(dentry_child1 || dentry_child2))
> -			return -EACCES;
> +			return false;
>   		/* For a simple request, only check for requested accesses. */
>   		access_masked_parent1 = access_request_parent1;
>   		access_masked_parent2 = access_request_parent2;
> @@ -622,24 +618,7 @@ static int check_access_path_dual(
>   	}
>   	path_put(&walker_path);
>   
> -	if (allowed_parent1 && allowed_parent2)
> -		return 0;
> -
> -	/*
> -	 * This prioritizes EACCES over EXDEV for all actions, including
> -	 * renames with RENAME_EXCHANGE.
> -	 */
> -	if (likely(is_eacces(layer_masks_parent1, access_request_parent1) ||
> -		   is_eacces(layer_masks_parent2, access_request_parent2)))
> -		return -EACCES;
> -
> -	/*
> -	 * Gracefully forbids reparenting if the destination directory
> -	 * hierarchy is not a superset of restrictions of the source directory
> -	 * hierarchy, or if LANDLOCK_ACCESS_FS_REFER is not allowed by the
> -	 * source or the destination.
> -	 */
> -	return -EXDEV;
> +	return allowed_parent1 && allowed_parent2;
>   }
>   
>   static inline int check_access_path(const struct landlock_ruleset *const domain,
> @@ -649,8 +628,10 @@ 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);
> -	return check_access_path_dual(domain, path, access_request,
> -				      &layer_masks, NULL, 0, NULL, NULL);
> +	if (is_access_to_paths_allowed(domain, path, access_request,
> +				       &layer_masks, NULL, 0, NULL, NULL))
> +		return 0;
> +	return -EACCES;
>   }
>   
>   static inline int current_check_access_path(const struct path *const path,
> @@ -711,8 +692,9 @@ static inline access_mask_t maybe_remove(const struct dentry *const dentry)
>    * file.  While walking from @dir to @mnt_root, we record all the domain's
>    * allowed accesses in @layer_masks_dom.
>    *
> - * This is similar to check_access_path_dual() but much simpler because it only
> - * handles walking on the same mount point and only check one set of accesses.
> + * This is similar to is_access_to_paths_allowed() but much simpler because it
> + * only handles walking on the same mount point and only checks one set of
> + * accesses.
>    *
>    * Returns:
>    * - true if all the domain access rights are allowed for @dir;
> @@ -857,10 +839,11 @@ 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);
> -		return check_access_path_dual(dom, new_dir,
> -					      access_request_parent1,
> -					      &layer_masks_parent1, NULL, 0,
> -					      NULL, NULL);
> +		if (is_access_to_paths_allowed(
> +			    dom, new_dir, access_request_parent1,
> +			    &layer_masks_parent1, NULL, 0, NULL, NULL))
> +			return 0;
> +		return -EACCES;
>   	}
>   
>   	access_request_parent1 |= LANDLOCK_ACCESS_FS_REFER;
> @@ -886,11 +869,27 @@ static int current_check_refer_path(struct dentry *const old_dentry,
>   	 * parent access rights.  This will be useful to compare with the
>   	 * destination parent access rights.
>   	 */
> -	return check_access_path_dual(dom, &mnt_dir, access_request_parent1,
> -				      &layer_masks_parent1, old_dentry,
> -				      access_request_parent2,
> -				      &layer_masks_parent2,
> -				      exchange ? new_dentry : NULL);
> +	if (is_access_to_paths_allowed(
> +		    dom, &mnt_dir, access_request_parent1, &layer_masks_parent1,
> +		    old_dentry, access_request_parent2, &layer_masks_parent2,
> +		    exchange ? new_dentry : NULL))
> +		return 0;
> +
> +	/*
> +	 * This prioritizes EACCES over EXDEV for all actions, including
> +	 * renames with RENAME_EXCHANGE.
> +	 */
> +	if (likely(is_eacces(&layer_masks_parent1, access_request_parent1) ||
> +		   is_eacces(&layer_masks_parent2, access_request_parent2)))
> +		return -EACCES;
> +
> +	/*
> +	 * Gracefully forbids reparenting if the destination directory
> +	 * hierarchy is not a superset of restrictions of the source directory
> +	 * hierarchy, or if LANDLOCK_ACCESS_FS_REFER is not allowed by the
> +	 * source or the destination.
> +	 */
> +	return -EXDEV;
>   }
>   
>   /* Inode hooks */