Replace get_raw_handled_fs_accesses() with a generic
landlock_merge_access_masks(), and replace the get_fs_domain()
implementation with a call to the new landlock_filter_access_masks()
helper.  These helpers will also be useful for other types of access.

Replace struct access_masks with union access_masks that includes a new
"all" field to simplify mask filtering.

Cc: Günther Noack <gnoack@google.com>
Cc: Mikhail Ivanov <ivanov.mikhail1@huawei-partners.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20241001141234.397649-2-mic@digikod.net
---
 security/landlock/fs.c       | 21 ++++-----------
 security/landlock/ruleset.h  | 51 +++++++++++++++++++++++++++---------
 security/landlock/syscalls.c |  2 +-
 3 files changed, 44 insertions(+), 30 deletions(-)

diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 7d79fc8abe21..a2ef7d151c81 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -388,33 +388,22 @@ static bool is_nouser_or_private(const struct dentry *dentry)
 		unlikely(IS_PRIVATE(d_backing_inode(dentry))));
 }
 
-static access_mask_t
-get_raw_handled_fs_accesses(const struct landlock_ruleset *const domain)
-{
-	access_mask_t access_dom = 0;
-	size_t layer_level;
-
-	for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
-		access_dom |=
-			landlock_get_raw_fs_access_mask(domain, layer_level);
-	return access_dom;
-}
-
 static access_mask_t
 get_handled_fs_accesses(const struct landlock_ruleset *const domain)
 {
 	/* Handles all initially denied by default access rights. */
-	return get_raw_handled_fs_accesses(domain) |
+	return landlock_merge_access_masks(domain).fs |
 	       LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
 }
 
 static const struct landlock_ruleset *
 get_fs_domain(const struct landlock_ruleset *const domain)
 {
-	if (!domain || !get_raw_handled_fs_accesses(domain))
-		return NULL;
+	const union access_masks all_fs = {
+		.fs = ~0,
+	};
 
-	return domain;
+	return landlock_filter_access_masks(domain, all_fs);
 }
 
 static const struct landlock_ruleset *get_current_fs_domain(void)
diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
index 61bdbc550172..a816042ca8f3 100644
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h
@@ -41,12 +41,19 @@ static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_SCOPE);
 static_assert(sizeof(unsigned long) >= sizeof(access_mask_t));
 
 /* Ruleset access masks. */
-struct access_masks {
-	access_mask_t fs : LANDLOCK_NUM_ACCESS_FS;
-	access_mask_t net : LANDLOCK_NUM_ACCESS_NET;
-	access_mask_t scope : LANDLOCK_NUM_SCOPE;
+union access_masks {
+	struct {
+		access_mask_t fs : LANDLOCK_NUM_ACCESS_FS;
+		access_mask_t net : LANDLOCK_NUM_ACCESS_NET;
+		access_mask_t scope : LANDLOCK_NUM_SCOPE;
+	};
+	u32 all;
 };
 
+/* Makes sure all fields are covered. */
+static_assert(sizeof(((union access_masks *)NULL)->all) ==
+	      sizeof(union access_masks));
+
 typedef u16 layer_mask_t;
 /* Makes sure all layers can be checked. */
 static_assert(BITS_PER_TYPE(layer_mask_t) >= LANDLOCK_MAX_NUM_LAYERS);
@@ -229,7 +236,7 @@ struct landlock_ruleset {
 			 * layers are set once and never changed for the
 			 * lifetime of the ruleset.
 			 */
-			struct access_masks access_masks[];
+			union access_masks access_masks[];
 		};
 	};
 };
@@ -260,6 +267,31 @@ static inline void landlock_get_ruleset(struct landlock_ruleset *const ruleset)
 		refcount_inc(&ruleset->usage);
 }
 
+static inline union access_masks
+landlock_merge_access_masks(const struct landlock_ruleset *const domain)
+{
+	size_t layer_level;
+	union access_masks matches = {};
+
+	for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
+		matches.all |= domain->access_masks[layer_level].all;
+
+	return matches;
+}
+
+static inline const struct landlock_ruleset *
+landlock_filter_access_masks(const struct landlock_ruleset *const domain,
+			     const union access_masks masks)
+{
+	if (!domain)
+		return NULL;
+
+	if (landlock_merge_access_masks(domain).all & masks.all)
+		return domain;
+
+	return NULL;
+}
+
 static inline void
 landlock_add_fs_access_mask(struct landlock_ruleset *const ruleset,
 			    const access_mask_t fs_access_mask,
@@ -295,19 +327,12 @@ landlock_add_scope_mask(struct landlock_ruleset *const ruleset,
 	ruleset->access_masks[layer_level].scope |= mask;
 }
 
-static inline access_mask_t
-landlock_get_raw_fs_access_mask(const struct landlock_ruleset *const ruleset,
-				const u16 layer_level)
-{
-	return ruleset->access_masks[layer_level].fs;
-}
-
 static inline access_mask_t
 landlock_get_fs_access_mask(const struct landlock_ruleset *const ruleset,
 			    const u16 layer_level)
 {
 	/* Handles all initially denied by default access rights. */
-	return landlock_get_raw_fs_access_mask(ruleset, layer_level) |
+	return ruleset->access_masks[layer_level].fs |
 	       LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
 }
 
diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
index f5a0e7182ec0..c097d356fa45 100644
--- a/security/landlock/syscalls.c
+++ b/security/landlock/syscalls.c
@@ -329,7 +329,7 @@ static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
 		return -ENOMSG;
 
 	/* Checks that allowed_access matches the @ruleset constraints. */
-	mask = landlock_get_raw_fs_access_mask(ruleset, 0);
+	mask = ruleset->access_masks[0].fs;
 	if ((path_beneath_attr.allowed_access | mask) != mask)
 		return -EINVAL;
 
-- 
2.46.1

On Tue, Oct 01, 2024 at 04:12:32PM +0200, Mickaël Salaün wrote:
> Replace get_raw_handled_fs_accesses() with a generic
> landlock_merge_access_masks(), and replace the get_fs_domain()
> implementation with a call to the new landlock_filter_access_masks()
> helper.  These helpers will also be useful for other types of access.
> 
> Replace struct access_masks with union access_masks that includes a new
> "all" field to simplify mask filtering.
> 
> Cc: Günther Noack <gnoack@google.com>
> Cc: Mikhail Ivanov <ivanov.mikhail1@huawei-partners.com>
> Signed-off-by: Mickaël Salaün <mic@digikod.net>
> Link: https://lore.kernel.org/r/20241001141234.397649-2-mic@digikod.net
> ---
>  security/landlock/fs.c       | 21 ++++-----------
>  security/landlock/ruleset.h  | 51 +++++++++++++++++++++++++++---------
>  security/landlock/syscalls.c |  2 +-
>  3 files changed, 44 insertions(+), 30 deletions(-)
> 
> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> index 7d79fc8abe21..a2ef7d151c81 100644
> --- a/security/landlock/fs.c
> +++ b/security/landlock/fs.c
> @@ -388,33 +388,22 @@ static bool is_nouser_or_private(const struct dentry *dentry)
>  		unlikely(IS_PRIVATE(d_backing_inode(dentry))));
>  }
>  
> -static access_mask_t
> -get_raw_handled_fs_accesses(const struct landlock_ruleset *const domain)
> -{
> -	access_mask_t access_dom = 0;
> -	size_t layer_level;
> -
> -	for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
> -		access_dom |=
> -			landlock_get_raw_fs_access_mask(domain, layer_level);
> -	return access_dom;
> -}
> -
>  static access_mask_t
>  get_handled_fs_accesses(const struct landlock_ruleset *const domain)
>  {
>  	/* Handles all initially denied by default access rights. */
> -	return get_raw_handled_fs_accesses(domain) |
> +	return landlock_merge_access_masks(domain).fs |
>  	       LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
>  }
>  
>  static const struct landlock_ruleset *
>  get_fs_domain(const struct landlock_ruleset *const domain)
>  {
> -	if (!domain || !get_raw_handled_fs_accesses(domain))
> -		return NULL;
> +	const union access_masks all_fs = {
> +		.fs = ~0,
> +	};
>  
> -	return domain;
> +	return landlock_filter_access_masks(domain, all_fs);
>  }
>  
>  static const struct landlock_ruleset *get_current_fs_domain(void)
> diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
> index 61bdbc550172..a816042ca8f3 100644
> --- a/security/landlock/ruleset.h
> +++ b/security/landlock/ruleset.h
> @@ -41,12 +41,19 @@ static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_SCOPE);
>  static_assert(sizeof(unsigned long) >= sizeof(access_mask_t));
>  
>  /* Ruleset access masks. */
> -struct access_masks {
> -	access_mask_t fs : LANDLOCK_NUM_ACCESS_FS;
> -	access_mask_t net : LANDLOCK_NUM_ACCESS_NET;
> -	access_mask_t scope : LANDLOCK_NUM_SCOPE;
> +union access_masks {
> +	struct {
> +		access_mask_t fs : LANDLOCK_NUM_ACCESS_FS;
> +		access_mask_t net : LANDLOCK_NUM_ACCESS_NET;
> +		access_mask_t scope : LANDLOCK_NUM_SCOPE;
> +	};
> +	u32 all;
>  };

More of a style remark:

I wonder whether it is worth turning this into a union.

If this is for performance, I do not think is buys you much.  With
optimization enabled, it does not make much of a difference whether
you are doing the & on .all or whether you are doing it on the
individual fields.  (I tried it out with gcc.  The only difference is
that the & on the individual fields will at the end mask only the bits
that belong to these fields.)

At the same time, in most places where struct access_masks is used,
the union is not necessary and might add to the confusion.


>  
> +/* Makes sure all fields are covered. */
> +static_assert(sizeof(((union access_masks *)NULL)->all) ==
> +	      sizeof(union access_masks));
> +
>  typedef u16 layer_mask_t;
>  /* Makes sure all layers can be checked. */
>  static_assert(BITS_PER_TYPE(layer_mask_t) >= LANDLOCK_MAX_NUM_LAYERS);
> @@ -229,7 +236,7 @@ struct landlock_ruleset {
>  			 * layers are set once and never changed for the
>  			 * lifetime of the ruleset.
>  			 */
> -			struct access_masks access_masks[];
> +			union access_masks access_masks[];
>  		};
>  	};
>  };
> @@ -260,6 +267,31 @@ static inline void landlock_get_ruleset(struct landlock_ruleset *const ruleset)
>  		refcount_inc(&ruleset->usage);
>  }
>  
> +static inline union access_masks
> +landlock_merge_access_masks(const struct landlock_ruleset *const domain)
> +{
> +	size_t layer_level;
> +	union access_masks matches = {};
> +
> +	for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
> +		matches.all |= domain->access_masks[layer_level].all;
> +
> +	return matches;
> +}
> +
> +static inline const struct landlock_ruleset *
> +landlock_filter_access_masks(const struct landlock_ruleset *const domain,
> +			     const union access_masks masks)

With this function name, the return type of this function is
unintuitive to me.  Judging by the name, I would have expected a
function that returns a "access_masks" value as well, similar to the
function one above (the remaining access rights after filtering)?

In the places where the result of this function is returned directly,
I find myself jumping back to the function implementation to
understand what this means.

As a constructive suggestion, how about calling this function
differently, e.g.

bool landlock_any_access_rights_handled(
    const struct landlock_ruleset *const domain,
    struct access_masks masks);

Then the callers who previously did

   return landlock_filter_access_masks(dom, masks);

would now do

   if (landlock_any_access_rights_handled(dom, masks))
       return dom;
   return NULL;

This is more verbose, but IMHO verbose code is not inherently bad,
if it is also clearer.  And it's only two lines more.

> +{
> +	if (!domain)
> +		return NULL;
> +
> +	if (landlock_merge_access_masks(domain).all & masks.all)
> +		return domain;
> +
> +	return NULL;
> +}

Function documentation for both functions would be good :)

> +
>  static inline void
>  landlock_add_fs_access_mask(struct landlock_ruleset *const ruleset,
>  			    const access_mask_t fs_access_mask,
> @@ -295,19 +327,12 @@ landlock_add_scope_mask(struct landlock_ruleset *const ruleset,
>  	ruleset->access_masks[layer_level].scope |= mask;
>  }
>  
> -static inline access_mask_t
> -landlock_get_raw_fs_access_mask(const struct landlock_ruleset *const ruleset,
> -				const u16 layer_level)
> -{
> -	return ruleset->access_masks[layer_level].fs;
> -}
> -
>  static inline access_mask_t
>  landlock_get_fs_access_mask(const struct landlock_ruleset *const ruleset,
>  			    const u16 layer_level)
>  {
>  	/* Handles all initially denied by default access rights. */
> -	return landlock_get_raw_fs_access_mask(ruleset, layer_level) |
> +	return ruleset->access_masks[layer_level].fs |
>  	       LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
>  }
>  
> diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
> index f5a0e7182ec0..c097d356fa45 100644
> --- a/security/landlock/syscalls.c
> +++ b/security/landlock/syscalls.c
> @@ -329,7 +329,7 @@ static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
>  		return -ENOMSG;
>  
>  	/* Checks that allowed_access matches the @ruleset constraints. */
> -	mask = landlock_get_raw_fs_access_mask(ruleset, 0);
> +	mask = ruleset->access_masks[0].fs;
>  	if ((path_beneath_attr.allowed_access | mask) != mask)
>  		return -EINVAL;
>  
> -- 
> 2.46.1
> 

Reviewed-by: Günther Noack <gnoack3000@gmail.com>

–Günther

On Sat, Oct 05, 2024 at 06:57:55PM +0200, Günther Noack wrote:
> On Tue, Oct 01, 2024 at 04:12:32PM +0200, Mickaël Salaün wrote:
> > Replace get_raw_handled_fs_accesses() with a generic
> > landlock_merge_access_masks(), and replace the get_fs_domain()
> > implementation with a call to the new landlock_filter_access_masks()
> > helper.  These helpers will also be useful for other types of access.
> > 
> > Replace struct access_masks with union access_masks that includes a new
> > "all" field to simplify mask filtering.
> > 
> > Cc: Günther Noack <gnoack@google.com>
> > Cc: Mikhail Ivanov <ivanov.mikhail1@huawei-partners.com>
> > Signed-off-by: Mickaël Salaün <mic@digikod.net>
> > Link: https://lore.kernel.org/r/20241001141234.397649-2-mic@digikod.net
> > ---
> >  security/landlock/fs.c       | 21 ++++-----------
> >  security/landlock/ruleset.h  | 51 +++++++++++++++++++++++++++---------
> >  security/landlock/syscalls.c |  2 +-
> >  3 files changed, 44 insertions(+), 30 deletions(-)
> > 
> > diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> > index 7d79fc8abe21..a2ef7d151c81 100644
> > --- a/security/landlock/fs.c
> > +++ b/security/landlock/fs.c
> > @@ -388,33 +388,22 @@ static bool is_nouser_or_private(const struct dentry *dentry)
> >  		unlikely(IS_PRIVATE(d_backing_inode(dentry))));
> >  }
> >  
> > -static access_mask_t
> > -get_raw_handled_fs_accesses(const struct landlock_ruleset *const domain)
> > -{
> > -	access_mask_t access_dom = 0;
> > -	size_t layer_level;
> > -
> > -	for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
> > -		access_dom |=
> > -			landlock_get_raw_fs_access_mask(domain, layer_level);
> > -	return access_dom;
> > -}
> > -
> >  static access_mask_t
> >  get_handled_fs_accesses(const struct landlock_ruleset *const domain)
> >  {
> >  	/* Handles all initially denied by default access rights. */
> > -	return get_raw_handled_fs_accesses(domain) |
> > +	return landlock_merge_access_masks(domain).fs |
> >  	       LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
> >  }
> >  
> >  static const struct landlock_ruleset *
> >  get_fs_domain(const struct landlock_ruleset *const domain)
> >  {
> > -	if (!domain || !get_raw_handled_fs_accesses(domain))
> > -		return NULL;
> > +	const union access_masks all_fs = {
> > +		.fs = ~0,
> > +	};
> >  
> > -	return domain;
> > +	return landlock_filter_access_masks(domain, all_fs);
> >  }
> >  
> >  static const struct landlock_ruleset *get_current_fs_domain(void)
> > diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
> > index 61bdbc550172..a816042ca8f3 100644
> > --- a/security/landlock/ruleset.h
> > +++ b/security/landlock/ruleset.h
> > @@ -41,12 +41,19 @@ static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_SCOPE);
> >  static_assert(sizeof(unsigned long) >= sizeof(access_mask_t));
> >  
> >  /* Ruleset access masks. */
> > -struct access_masks {
> > -	access_mask_t fs : LANDLOCK_NUM_ACCESS_FS;
> > -	access_mask_t net : LANDLOCK_NUM_ACCESS_NET;
> > -	access_mask_t scope : LANDLOCK_NUM_SCOPE;
> > +union access_masks {
> > +	struct {
> > +		access_mask_t fs : LANDLOCK_NUM_ACCESS_FS;
> > +		access_mask_t net : LANDLOCK_NUM_ACCESS_NET;
> > +		access_mask_t scope : LANDLOCK_NUM_SCOPE;
> > +	};
> > +	u32 all;
> >  };
> 
> More of a style remark:
> 
> I wonder whether it is worth turning this into a union.
> 
> If this is for performance, I do not think is buys you much.  With
> optimization enabled, it does not make much of a difference whether
> you are doing the & on .all or whether you are doing it on the
> individual fields.  (I tried it out with gcc.  The only difference is
> that the & on the individual fields will at the end mask only the bits
> that belong to these fields.)

This is not about performance but about maintainability and simplicity
(to avoid future changes/errors).  Indeed, with this "all" field we
don't need to update (or forget to update) the
landlock_merge_access_masks() helper.  This function can be simple and
generic to be used in the fs.c, net.c, and scope.c files.

> 
> At the same time, in most places where struct access_masks is used,
> the union is not necessary and might add to the confusion.

I think it should not be an issue, and it leverages the advantages of
the previous access_masks_t with the ones of struct access_masks.

> 
> 
> >  
> > +/* Makes sure all fields are covered. */
> > +static_assert(sizeof(((union access_masks *)NULL)->all) ==
> > +	      sizeof(union access_masks));
> > +
> >  typedef u16 layer_mask_t;
> >  /* Makes sure all layers can be checked. */
> >  static_assert(BITS_PER_TYPE(layer_mask_t) >= LANDLOCK_MAX_NUM_LAYERS);
> > @@ -229,7 +236,7 @@ struct landlock_ruleset {
> >  			 * layers are set once and never changed for the
> >  			 * lifetime of the ruleset.
> >  			 */
> > -			struct access_masks access_masks[];
> > +			union access_masks access_masks[];
> >  		};
> >  	};
> >  };
> > @@ -260,6 +267,31 @@ static inline void landlock_get_ruleset(struct landlock_ruleset *const ruleset)
> >  		refcount_inc(&ruleset->usage);
> >  }
> >  
> > +static inline union access_masks
> > +landlock_merge_access_masks(const struct landlock_ruleset *const domain)
> > +{
> > +	size_t layer_level;
> > +	union access_masks matches = {};
> > +
> > +	for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
> > +		matches.all |= domain->access_masks[layer_level].all;
> > +
> > +	return matches;
> > +}
> > +
> > +static inline const struct landlock_ruleset *
> > +landlock_filter_access_masks(const struct landlock_ruleset *const domain,
> > +			     const union access_masks masks)
> 
> With this function name, the return type of this function is
> unintuitive to me.  Judging by the name, I would have expected a
> function that returns a "access_masks" value as well, similar to the
> function one above (the remaining access rights after filtering)?

Fair

> 
> In the places where the result of this function is returned directly,
> I find myself jumping back to the function implementation to
> understand what this means.
> 
> As a constructive suggestion, how about calling this function
> differently, e.g.
> 
> bool landlock_any_access_rights_handled(
>     const struct landlock_ruleset *const domain,
>     struct access_masks masks);
> 
> Then the callers who previously did
> 
>    return landlock_filter_access_masks(dom, masks);
> 
> would now do
> 
>    if (landlock_any_access_rights_handled(dom, masks))
>        return dom;
>    return NULL;

I'm not sure if you're suggesting to return an union access_masks or a
landlock_ruleset pointer.  Returning a ruleset/domain simplifies the
work of callers so I'd prefer to keep that.

The "_any_access_rights_handled" doesn't have a verb, and it's not clear
to me if it would return the handled access rights or something else.

What about renaming it landlock_mask_ruleset(dom, access_masks) instead?

For now, the variables named "domain" points to struct landlock_ruleset,
but they will eventually point to a future struct landlock_domain.  So,
I prefer to keep the name "ruleset" in helpers dealing with struct
landlock_ruleset.  We'll need to change these helpers when we'll switch
to landlock_domain anyway.

> 
> This is more verbose, but IMHO verbose code is not inherently bad,
> if it is also clearer.  And it's only two lines more.
> 
> > +{
> > +	if (!domain)
> > +		return NULL;
> > +
> > +	if (landlock_merge_access_masks(domain).all & masks.all)
> > +		return domain;
> > +
> > +	return NULL;
> > +}
> 
> Function documentation for both functions would be good :)

Indeed :)

> 
> > +
> >  static inline void
> >  landlock_add_fs_access_mask(struct landlock_ruleset *const ruleset,
> >  			    const access_mask_t fs_access_mask,
> > @@ -295,19 +327,12 @@ landlock_add_scope_mask(struct landlock_ruleset *const ruleset,
> >  	ruleset->access_masks[layer_level].scope |= mask;
> >  }
> >  
> > -static inline access_mask_t
> > -landlock_get_raw_fs_access_mask(const struct landlock_ruleset *const ruleset,
> > -				const u16 layer_level)
> > -{
> > -	return ruleset->access_masks[layer_level].fs;
> > -}
> > -
> >  static inline access_mask_t
> >  landlock_get_fs_access_mask(const struct landlock_ruleset *const ruleset,
> >  			    const u16 layer_level)
> >  {
> >  	/* Handles all initially denied by default access rights. */
> > -	return landlock_get_raw_fs_access_mask(ruleset, layer_level) |
> > +	return ruleset->access_masks[layer_level].fs |
> >  	       LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
> >  }
> >  
> > diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
> > index f5a0e7182ec0..c097d356fa45 100644
> > --- a/security/landlock/syscalls.c
> > +++ b/security/landlock/syscalls.c
> > @@ -329,7 +329,7 @@ static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
> >  		return -ENOMSG;
> >  
> >  	/* Checks that allowed_access matches the @ruleset constraints. */
> > -	mask = landlock_get_raw_fs_access_mask(ruleset, 0);
> > +	mask = ruleset->access_masks[0].fs;
> >  	if ((path_beneath_attr.allowed_access | mask) != mask)
> >  		return -EINVAL;
> >  
> > -- 
> > 2.46.1
> > 
> 
> Reviewed-by: Günther Noack <gnoack3000@gmail.com>
> 
> –Günther
> 

On Mon, Oct 07, 2024 at 03:00:34PM +0200, Mickaël Salaün wrote:
> On Sat, Oct 05, 2024 at 06:57:55PM +0200, Günther Noack wrote:
> > On Tue, Oct 01, 2024 at 04:12:32PM +0200, Mickaël Salaün wrote:
> > > Replace get_raw_handled_fs_accesses() with a generic
> > > landlock_merge_access_masks(), and replace the get_fs_domain()
> > > implementation with a call to the new landlock_filter_access_masks()
> > > helper.  These helpers will also be useful for other types of access.
> > > 
> > > Replace struct access_masks with union access_masks that includes a new
> > > "all" field to simplify mask filtering.
> > > 
> > > Cc: Günther Noack <gnoack@google.com>
> > > Cc: Mikhail Ivanov <ivanov.mikhail1@huawei-partners.com>
> > > Signed-off-by: Mickaël Salaün <mic@digikod.net>
> > > Link: https://lore.kernel.org/r/20241001141234.397649-2-mic@digikod.net
> > > ---
> > >  security/landlock/fs.c       | 21 ++++-----------
> > >  security/landlock/ruleset.h  | 51 +++++++++++++++++++++++++++---------
> > >  security/landlock/syscalls.c |  2 +-
> > >  3 files changed, 44 insertions(+), 30 deletions(-)
> > > 
> > > diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> > > index 7d79fc8abe21..a2ef7d151c81 100644
> > > --- a/security/landlock/fs.c
> > > +++ b/security/landlock/fs.c
> > > @@ -388,33 +388,22 @@ static bool is_nouser_or_private(const struct dentry *dentry)
> > >  		unlikely(IS_PRIVATE(d_backing_inode(dentry))));
> > >  }
> > >  
> > > -static access_mask_t
> > > -get_raw_handled_fs_accesses(const struct landlock_ruleset *const domain)
> > > -{
> > > -	access_mask_t access_dom = 0;
> > > -	size_t layer_level;
> > > -
> > > -	for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
> > > -		access_dom |=
> > > -			landlock_get_raw_fs_access_mask(domain, layer_level);
> > > -	return access_dom;
> > > -}
> > > -
> > >  static access_mask_t
> > >  get_handled_fs_accesses(const struct landlock_ruleset *const domain)
> > >  {
> > >  	/* Handles all initially denied by default access rights. */
> > > -	return get_raw_handled_fs_accesses(domain) |
> > > +	return landlock_merge_access_masks(domain).fs |
> > >  	       LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
> > >  }
> > >  
> > >  static const struct landlock_ruleset *
> > >  get_fs_domain(const struct landlock_ruleset *const domain)
> > >  {
> > > -	if (!domain || !get_raw_handled_fs_accesses(domain))
> > > -		return NULL;
> > > +	const union access_masks all_fs = {
> > > +		.fs = ~0,
> > > +	};
> > >  
> > > -	return domain;
> > > +	return landlock_filter_access_masks(domain, all_fs);
> > >  }
> > >  
> > >  static const struct landlock_ruleset *get_current_fs_domain(void)
> > > diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
> > > index 61bdbc550172..a816042ca8f3 100644
> > > --- a/security/landlock/ruleset.h
> > > +++ b/security/landlock/ruleset.h
> > > @@ -41,12 +41,19 @@ static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_SCOPE);
> > >  static_assert(sizeof(unsigned long) >= sizeof(access_mask_t));
> > >  
> > >  /* Ruleset access masks. */
> > > -struct access_masks {
> > > -	access_mask_t fs : LANDLOCK_NUM_ACCESS_FS;
> > > -	access_mask_t net : LANDLOCK_NUM_ACCESS_NET;
> > > -	access_mask_t scope : LANDLOCK_NUM_SCOPE;
> > > +union access_masks {
> > > +	struct {
> > > +		access_mask_t fs : LANDLOCK_NUM_ACCESS_FS;
> > > +		access_mask_t net : LANDLOCK_NUM_ACCESS_NET;
> > > +		access_mask_t scope : LANDLOCK_NUM_SCOPE;
> > > +	};
> > > +	u32 all;
> > >  };
> > 
> > More of a style remark:
> > 
> > I wonder whether it is worth turning this into a union.
> > 
> > If this is for performance, I do not think is buys you much.  With
> > optimization enabled, it does not make much of a difference whether
> > you are doing the & on .all or whether you are doing it on the
> > individual fields.  (I tried it out with gcc.  The only difference is
> > that the & on the individual fields will at the end mask only the bits
> > that belong to these fields.)
> 
> This is not about performance but about maintainability and simplicity
> (to avoid future changes/errors).  Indeed, with this "all" field we
> don't need to update (or forget to update) the
> landlock_merge_access_masks() helper.  This function can be simple and
> generic to be used in the fs.c, net.c, and scope.c files.
> 
> > 
> > At the same time, in most places where struct access_masks is used,
> > the union is not necessary and might add to the confusion.
> 
> I think it should not be an issue, and it leverages the advantages of
> the previous access_masks_t with the ones of struct access_masks.
> 
> > 
> > 
> > >  
> > > +/* Makes sure all fields are covered. */
> > > +static_assert(sizeof(((union access_masks *)NULL)->all) ==
> > > +	      sizeof(union access_masks));
> > > +
> > >  typedef u16 layer_mask_t;
> > >  /* Makes sure all layers can be checked. */
> > >  static_assert(BITS_PER_TYPE(layer_mask_t) >= LANDLOCK_MAX_NUM_LAYERS);
> > > @@ -229,7 +236,7 @@ struct landlock_ruleset {
> > >  			 * layers are set once and never changed for the
> > >  			 * lifetime of the ruleset.
> > >  			 */
> > > -			struct access_masks access_masks[];
> > > +			union access_masks access_masks[];
> > >  		};
> > >  	};
> > >  };
> > > @@ -260,6 +267,31 @@ static inline void landlock_get_ruleset(struct landlock_ruleset *const ruleset)
> > >  		refcount_inc(&ruleset->usage);
> > >  }
> > >  
> > > +static inline union access_masks
> > > +landlock_merge_access_masks(const struct landlock_ruleset *const domain)
> > > +{
> > > +	size_t layer_level;
> > > +	union access_masks matches = {};
> > > +
> > > +	for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
> > > +		matches.all |= domain->access_masks[layer_level].all;
> > > +
> > > +	return matches;
> > > +}
> > > +
> > > +static inline const struct landlock_ruleset *
> > > +landlock_filter_access_masks(const struct landlock_ruleset *const domain,
> > > +			     const union access_masks masks)
> > 
> > With this function name, the return type of this function is
> > unintuitive to me.  Judging by the name, I would have expected a
> > function that returns a "access_masks" value as well, similar to the
> > function one above (the remaining access rights after filtering)?
> 
> Fair
> 
> > 
> > In the places where the result of this function is returned directly,
> > I find myself jumping back to the function implementation to
> > understand what this means.
> > 
> > As a constructive suggestion, how about calling this function
> > differently, e.g.
> > 
> > bool landlock_any_access_rights_handled(
> >     const struct landlock_ruleset *const domain,
> >     struct access_masks masks);
> > 
> > Then the callers who previously did
> > 
> >    return landlock_filter_access_masks(dom, masks);
> > 
> > would now do
> > 
> >    if (landlock_any_access_rights_handled(dom, masks))
> >        return dom;
> >    return NULL;
> 
> I'm not sure if you're suggesting to return an union access_masks or a
> landlock_ruleset pointer.  Returning a ruleset/domain simplifies the
> work of callers so I'd prefer to keep that.
> 
> The "_any_access_rights_handled" doesn't have a verb, and it's not clear
> to me if it would return the handled access rights or something else.
> 
> What about renaming it landlock_mask_ruleset(dom, access_masks) instead?

Thinking more about it, using "mask" could mean that the access_masks
argument will indeed mask and we'll get the oposite.  What about
landlock_match_ruleset()?

> 
> For now, the variables named "domain" points to struct landlock_ruleset,
> but they will eventually point to a future struct landlock_domain.  So,
> I prefer to keep the name "ruleset" in helpers dealing with struct
> landlock_ruleset.  We'll need to change these helpers when we'll switch
> to landlock_domain anyway.
> 
> > 
> > This is more verbose, but IMHO verbose code is not inherently bad,
> > if it is also clearer.  And it's only two lines more.