Re: [PATCH v8 01/12] landlock: Make ruleset's access masks more generic

["Mickaël Salaün" <mic@digikod.net>]

On 21/10/2022 17:26, Konstantin Meskhidze wrote:
> To support network type rules, this modification renames ruleset's
> access masks and modifies it's type to access_masks_t. This patch
> adds filesystem helper functions to add and get filesystem mask.
> 
> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
> ---
> 
> Changes since v7:
> * Refactors commit message.
> 
> Changes since v6:
> * Adds a new access_masks_t for struct ruleset.
> * Renames landlock_set_fs_access_mask() to landlock_add_fs_access_mask()
>    because it OR values.
> * Makes landlock_add_fs_access_mask() more resilient incorrect values.
> * Refactors landlock_get_fs_access_mask().
> 
> Changes since v6:
> * Adds a new access_masks_t for struct ruleset.
> * Renames landlock_set_fs_access_mask() to landlock_add_fs_access_mask()
>    because it OR values.
> * Makes landlock_add_fs_access_mask() more resilient incorrect values.
> * Refactors landlock_get_fs_access_mask().
> 
> Changes since v5:
> * Changes access_mask_t to u32.
> * Formats code with clang-format-14.
> 
> Changes since v4:
> * Deletes struct landlock_access_mask.
> 
> Changes since v3:
> * Splits commit.
> * Adds get_mask, set_mask helpers for filesystem.
> * Adds new struct landlock_access_mask.
> 
> ---
>   security/landlock/fs.c       | 10 +++++-----
>   security/landlock/limits.h   |  1 +
>   security/landlock/ruleset.c  | 17 +++++++++--------
>   security/landlock/ruleset.h  | 35 +++++++++++++++++++++++++++++++----
>   security/landlock/syscalls.c |  7 ++++---
>   5 files changed, 50 insertions(+), 20 deletions(-)
> 
> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> index adcea0fe7e68..0d57c6479d29 100644
> --- a/security/landlock/fs.c
> +++ b/security/landlock/fs.c
> @@ -178,9 +178,9 @@ int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
>   		return -EINVAL;
> 
>   	/* Transforms relative access rights to absolute ones. */
> -	access_rights |=
> -		LANDLOCK_MASK_ACCESS_FS &
> -		~(ruleset->fs_access_masks[0] | ACCESS_INITIALLY_DENIED);
> +	access_rights |= LANDLOCK_MASK_ACCESS_FS &
> +			 ~(landlock_get_fs_access_mask(ruleset, 0) |
> +			   ACCESS_INITIALLY_DENIED);
>   	object = get_inode_object(d_backing_inode(path->dentry));
>   	if (IS_ERR(object))
>   		return PTR_ERR(object);
> @@ -294,7 +294,7 @@ get_handled_accesses(const struct landlock_ruleset *const domain)
>   	size_t layer_level;
> 
>   	for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
> -		access_dom |= domain->fs_access_masks[layer_level];
> +		access_dom |= landlock_get_fs_access_mask(domain, layer_level);
>   	return access_dom & LANDLOCK_MASK_ACCESS_FS;

You can remove `& LANDLOCK_MASK_ACCESS_FS` here because it is now part 
of landlock_get_fs_access_mask().


>   }
> 
> @@ -336,7 +336,7 @@ init_layer_masks(const struct landlock_ruleset *const domain,
>   			 * access rights.
>   			 */
>   			if (BIT_ULL(access_bit) &
> -			    (domain->fs_access_masks[layer_level] |
> +			    (landlock_get_fs_access_mask(domain, layer_level) |
>   			     ACCESS_INITIALLY_DENIED)) {
>   				(*layer_masks)[access_bit] |=
>   					BIT_ULL(layer_level);
> diff --git a/security/landlock/limits.h b/security/landlock/limits.h
> index 82288f0e9e5e..bafb3b8dc677 100644
> --- a/security/landlock/limits.h
> +++ b/security/landlock/limits.h
> @@ -21,6 +21,7 @@
>   #define LANDLOCK_LAST_ACCESS_FS		LANDLOCK_ACCESS_FS_TRUNCATE
>   #define LANDLOCK_MASK_ACCESS_FS		((LANDLOCK_LAST_ACCESS_FS << 1) - 1)
>   #define LANDLOCK_NUM_ACCESS_FS		__const_hweight64(LANDLOCK_MASK_ACCESS_FS)
> +#define LANDLOCK_SHIFT_ACCESS_FS	0
> 
>   /* clang-format on */
> 
> diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
> index 996484f98bfd..1f3188b4e313 100644
> --- a/security/landlock/ruleset.c
> +++ b/security/landlock/ruleset.c
> @@ -29,7 +29,7 @@ static struct landlock_ruleset *create_ruleset(const u32 num_layers)
>   	struct landlock_ruleset *new_ruleset;
> 
>   	new_ruleset =
> -		kzalloc(struct_size(new_ruleset, fs_access_masks, num_layers),
> +		kzalloc(struct_size(new_ruleset, access_masks, num_layers),
>   			GFP_KERNEL_ACCOUNT);
>   	if (!new_ruleset)
>   		return ERR_PTR(-ENOMEM);
> @@ -40,7 +40,7 @@ static struct landlock_ruleset *create_ruleset(const u32 num_layers)
>   	/*
>   	 * hierarchy = NULL
>   	 * num_rules = 0
> -	 * fs_access_masks[] = 0
> +	 * access_masks[] = 0
>   	 */
>   	return new_ruleset;
>   }
> @@ -55,7 +55,7 @@ landlock_create_ruleset(const access_mask_t fs_access_mask)
>   		return ERR_PTR(-ENOMSG);
>   	new_ruleset = create_ruleset(1);
>   	if (!IS_ERR(new_ruleset))
> -		new_ruleset->fs_access_masks[0] = fs_access_mask;
> +		landlock_add_fs_access_mask(new_ruleset, fs_access_mask, 0);
>   	return new_ruleset;
>   }
> 
> @@ -117,11 +117,12 @@ static void build_check_ruleset(void)
>   		.num_rules = ~0,
>   		.num_layers = ~0,
>   	};
> -	typeof(ruleset.fs_access_masks[0]) fs_access_mask = ~0;
> +	typeof(ruleset.access_masks[0]) access_masks = ~0;
> 
>   	BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES);
>   	BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS);
> -	BUILD_BUG_ON(fs_access_mask < LANDLOCK_MASK_ACCESS_FS);
> +	BUILD_BUG_ON(access_masks <
> +		     (LANDLOCK_MASK_ACCESS_FS << LANDLOCK_SHIFT_ACCESS_FS));
>   }
> 
>   /**
> @@ -281,7 +282,7 @@ static int merge_ruleset(struct landlock_ruleset *const dst,
>   		err = -EINVAL;
>   		goto out_unlock;
>   	}
> -	dst->fs_access_masks[dst->num_layers - 1] = src->fs_access_masks[0];
> +	dst->access_masks[dst->num_layers - 1] = src->access_masks[0];
> 
>   	/* Merges the @src tree. */
>   	rbtree_postorder_for_each_entry_safe(walker_rule, next_rule, &src->root,
> @@ -340,8 +341,8 @@ static int inherit_ruleset(struct landlock_ruleset *const parent,
>   		goto out_unlock;
>   	}
>   	/* Copies the parent layer stack and leaves a space for the new layer. */
> -	memcpy(child->fs_access_masks, parent->fs_access_masks,
> -	       flex_array_size(parent, fs_access_masks, parent->num_layers));
> +	memcpy(child->access_masks, parent->access_masks,
> +	       flex_array_size(parent, access_masks, parent->num_layers));
> 
>   	if (WARN_ON_ONCE(!parent->hierarchy)) {
>   		err = -EINVAL;
> diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
> index d43231b783e4..f2ad932d396c 100644
> --- a/security/landlock/ruleset.h
> +++ b/security/landlock/ruleset.h
> @@ -25,6 +25,11 @@ static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS);
>   /* Makes sure for_each_set_bit() and for_each_clear_bit() calls are OK. */
>   static_assert(sizeof(unsigned long) >= sizeof(access_mask_t));
> 
> +/* Ruleset access masks. */
> +typedef u16 access_masks_t;
> +/* Makes sure all ruleset access rights can be stored. */
> +static_assert(BITS_PER_TYPE(access_masks_t) >= LANDLOCK_NUM_ACCESS_FS);
> +
>   typedef u16 layer_mask_t;
>   /* Makes sure all layers can be checked. */
>   static_assert(BITS_PER_TYPE(layer_mask_t) >= LANDLOCK_MAX_NUM_LAYERS);
> @@ -110,7 +115,7 @@ struct landlock_ruleset {
>   		 * section.  This is only used by
>   		 * landlock_put_ruleset_deferred() when @usage reaches zero.
>   		 * The fields @lock, @usage, @num_rules, @num_layers and
> -		 * @fs_access_masks are then unused.
> +		 * @access_masks are then unused.
>   		 */
>   		struct work_struct work_free;
>   		struct {
> @@ -137,7 +142,7 @@ struct landlock_ruleset {
>   			 */
>   			u32 num_layers;
>   			/**
> -			 * @fs_access_masks: Contains the subset of filesystem
> +			 * @access_masks: Contains the subset of filesystem
>   			 * actions that are restricted by a ruleset.  A domain
>   			 * saves all layers of merged rulesets in a stack
>   			 * (FAM), starting from the first layer to the last
> @@ -148,13 +153,13 @@ struct landlock_ruleset {
>   			 * layers are set once and never changed for the
>   			 * lifetime of the ruleset.
>   			 */
> -			access_mask_t fs_access_masks[];
> +			access_masks_t access_masks[];
>   		};
>   	};
>   };
> 
>   struct landlock_ruleset *
> -landlock_create_ruleset(const access_mask_t fs_access_mask);
> +landlock_create_ruleset(const access_mask_t access_mask);
> 
>   void landlock_put_ruleset(struct landlock_ruleset *const ruleset);
>   void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset);
> @@ -177,4 +182,26 @@ static inline void landlock_get_ruleset(struct landlock_ruleset *const ruleset)
>   		refcount_inc(&ruleset->usage);
>   }
> 
> +static inline void
> +landlock_add_fs_access_mask(struct landlock_ruleset *const ruleset,
> +			    const access_mask_t fs_access_mask,
> +			    const u16 layer_level)
> +{
> +	access_mask_t fs_mask = fs_access_mask & LANDLOCK_MASK_ACCESS_FS;
> +
> +	/* Should already be checked in sys_landlock_create_ruleset(). */
> +	WARN_ON_ONCE(fs_access_mask != fs_mask);
> +	// TODO: Add tests to check "|=" and not "="

This todo should be done and removed. No more todos must remain.


> +	ruleset->access_masks[layer_level] |=
> +		(fs_mask << LANDLOCK_SHIFT_ACCESS_FS);
> +}
> +
> +static inline access_mask_t
> +landlock_get_fs_access_mask(const struct landlock_ruleset *const ruleset,
> +			    const u16 layer_level)
> +{
> +	return (ruleset->access_masks[layer_level] >>
> +		LANDLOCK_SHIFT_ACCESS_FS) &
> +	       LANDLOCK_MASK_ACCESS_FS;
> +}
>   #endif /* _SECURITY_LANDLOCK_RULESET_H */
> diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
> index 245cc650a4dc..71aca7f990bc 100644
> --- a/security/landlock/syscalls.c
> +++ b/security/landlock/syscalls.c
> @@ -346,10 +346,11 @@ SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
>   	}
>   	/*
>   	 * Checks that allowed_access matches the @ruleset constraints
> -	 * (ruleset->fs_access_masks[0] is automatically upgraded to 64-bits).
> +	 * (ruleset->access_masks[0] is automatically upgraded to 64-bits).
>   	 */
> -	if ((path_beneath_attr.allowed_access | ruleset->fs_access_masks[0]) !=
> -	    ruleset->fs_access_masks[0]) {
> +	if ((path_beneath_attr.allowed_access |
> +	     landlock_get_fs_access_mask(ruleset, 0)) !=
> +	    landlock_get_fs_access_mask(ruleset, 0)) {
>   		err = -EINVAL;
>   		goto out_put_ruleset;
>   	}
> --
> 2.25.1
> 

I'll send a patch to be applied after this one.