[PATCH] landlock: Drop "const" argument qualifier to avoid GCC 4.9 warnings

When building under GCC 4.9, the compiler warns about const mismatches:

security/landlock/ruleset.c: In function 'insert_rule':
security/landlock/ruleset.c:196:34: error: passing argument 2 of 'create_rule' from incompatible pointer type [-Werror]
   new_rule = create_rule(object, &this->layers, this->num_layers,
                                  ^
security/landlock/ruleset.c:69:30: note: expected 'const struct landlock_layer ** const' but argument is of type 'struct landlock_layer (*)[]'
 static struct landlock_rule *create_rule(
                              ^
security/landlock/ruleset.c: In function 'landlock_insert_rule':
security/landlock/ruleset.c:240:38: error: passing argument 3 of 'insert_rule' from incompatible pointer type [-Werror]
  return insert_rule(ruleset, object, &layers, ARRAY_SIZE(layers));
                                      ^
security/landlock/ruleset.c:144:12: note: expected 'const struct landlock_layer ** const' but argument is of type 'struct landlock_layer (*)[1]'
 static int insert_rule(struct landlock_ruleset *const ruleset,
            ^

Drop "const" from the function definition.

Cc: "Mickaël Salaün" <mic@digikod.net>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: linux-security-module@vger.kernel.org
Signed-off-by: Kees Cook <redacted>
---
 security/landlock/ruleset.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index ec72b9262bf3..64c37af88ee7 100644
--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c

@@ -68,7 +68,7 @@ static void build_check_rule(void)
 
 static struct landlock_rule *create_rule(
 		struct landlock_object *const object,
-		const struct landlock_layer (*const layers)[],
+		struct landlock_layer (*layers)[],
 		const u32 num_layers,
 		const struct landlock_layer *const new_layer)
 {

@@ -143,7 +143,7 @@ static void build_check_ruleset(void)
  */
 static int insert_rule(struct landlock_ruleset *const ruleset,
 		struct landlock_object *const object,
-		const struct landlock_layer (*const layers)[],
+		struct landlock_layer (*layers)[],
 		size_t num_layers)
 {
 	struct rb_node **walker_node;

-- 
2.30.2

On 11/09/2021 00:36, Kees Cook wrote:

When building under GCC 4.9, the compiler warns about const mismatches:

security/landlock/ruleset.c: In function 'insert_rule':
security/landlock/ruleset.c:196:34: error: passing argument 2 of 'create_rule' from incompatible pointer type [-Werror]
   new_rule = create_rule(object, &this->layers, this->num_layers,
                                  ^
security/landlock/ruleset.c:69:30: note: expected 'const struct landlock_layer ** const' but argument is of type 'struct landlock_layer (*)[]'
 static struct landlock_rule *create_rule(
                              ^
security/landlock/ruleset.c: In function 'landlock_insert_rule':
security/landlock/ruleset.c:240:38: error: passing argument 3 of 'insert_rule' from incompatible pointer type [-Werror]
  return insert_rule(ruleset, object, &layers, ARRAY_SIZE(layers));
                                      ^
security/landlock/ruleset.c:144:12: note: expected 'const struct landlock_layer ** const' but argument is of type 'struct landlock_layer (*)[1]'
 static int insert_rule(struct landlock_ruleset *const ruleset,

I guess this is a bug in GCC 4.9 (i.e. missing automatic const upgrade).
Couldn't we backport a fix to GCC 4.9 instead?

The "const layers" is not an issue, it should not be removed.

Same here for the second const.

 		size_t num_layers)
 {
 	struct rb_node **walker_node;

On Mon, Sep 13, 2021 at 01:19:19PM +0200, Mickaël Salaün wrote:

On 11/09/2021 00:36, Kees Cook wrote:

quoted

When building under GCC 4.9, the compiler warns about const mismatches:

security/landlock/ruleset.c: In function 'insert_rule':
security/landlock/ruleset.c:196:34: error: passing argument 2 of 'create_rule' from incompatible pointer type [-Werror]
   new_rule = create_rule(object, &this->layers, this->num_layers,
                                  ^
security/landlock/ruleset.c:69:30: note: expected 'const struct landlock_layer ** const' but argument is of type 'struct landlock_layer (*)[]'
 static struct landlock_rule *create_rule(
                              ^
security/landlock/ruleset.c: In function 'landlock_insert_rule':
security/landlock/ruleset.c:240:38: error: passing argument 3 of 'insert_rule' from incompatible pointer type [-Werror]
  return insert_rule(ruleset, object, &layers, ARRAY_SIZE(layers));
                                      ^
security/landlock/ruleset.c:144:12: note: expected 'const struct landlock_layer ** const' but argument is of type 'struct landlock_layer (*)[1]'
 static int insert_rule(struct landlock_ruleset *const ruleset,

I guess this is a bug in GCC 4.9 (i.e. missing automatic const upgrade).
Couldn't we backport a fix to GCC 4.9 instead?

I don't disagree, but I'm just trying to deal with the fall-out of
-Werror. Perhaps speak up on this thread in support of deprecating
GCC 4.9?

https://lore.kernel.org/lkml/20210910234047.1019925-1-ndesaulniers@google.com/

-Kees

-- 
Kees Cook