[PATCH v13 07/12] landlock: Refactor landlock_add_rule() syscall

[Mickaël Salaün]

On Mon, Oct 16, 2023 at 09:50:25AM +0800, Konstantin Meskhidze wrote:
> Change the landlock_add_rule() syscall to support new rule types
> in future Landlock versions. Add the add_rule_path_beneath() helper
> to support current filesystem rules.
> 
> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze at huawei.com>
> Link: https://lore.kernel.org/r/20230920092641.832134-8-konstantin.meskhidze@huawei.com
> Signed-off-by: Mickaël Salaün <mic at digikod.net>
> ---
> 
> Changes since v12:
> * None.
> 
> Changes since v11:
> * None.
> 
> Changes since v10:
> * None.
> 
> Changes since v9:
> * Minor fixes:
> 	- deletes unnecessary curly braces.
> 	- deletes unnecessary empty line.
> 
> Changes since v8:
> * Refactors commit message.
> * Minor fixes.
> 
> Changes since v7:
> * None
> 
> Changes since v6:
> * None
> 
> Changes since v5:
> * Refactors syscall landlock_add_rule() and add_rule_path_beneath() helper
> to make argument check ordering consistent and get rid of partial revertings
> in following patches.
> * Rolls back refactoring base_test.c seltest.
> * Formats code with clang-format-14.
> 
> Changes since v4:
> * Refactors add_rule_path_beneath() and landlock_add_rule() functions
> to optimize code usage.
> * Refactors base_test.c seltest: adds LANDLOCK_RULE_PATH_BENEATH
> rule type in landlock_add_rule() call.
> 
> Changes since v3:
> * Split commit.
> * Refactors landlock_add_rule syscall.
> 
> ---
>  security/landlock/syscalls.c | 92 +++++++++++++++++++-----------------
>  1 file changed, 48 insertions(+), 44 deletions(-)
> 
> diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
> index d35cd5d304db..8a54e87dbb17 100644
> --- a/security/landlock/syscalls.c
> +++ b/security/landlock/syscalls.c
> @@ -274,6 +274,47 @@ static int get_path_from_fd(const s32 fd, struct path *const path)
>  	return err;
>  }
> 
> +static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
> +				 const void __user *const rule_attr)
> +{
> +	struct landlock_path_beneath_attr path_beneath_attr;
> +	struct path path;
> +	int res, err;
> +	access_mask_t mask;
> +
> +	/* Copies raw user space buffer, only one type for now. */
> +	res = copy_from_user(&path_beneath_attr, rule_attr,
> +			     sizeof(path_beneath_attr));
> +	if (res)
> +		return -EFAULT;
> +
> +	/*
> +	 * Informs about useless rule: empty allowed_access (i.e. deny rules)
> +	 * are ignored in path walks.
> +	 */
> +	if (!path_beneath_attr.allowed_access)
> +		return -ENOMSG;
> +
> +	/*
> +	 * Checks that allowed_access matches the @ruleset constraints
> +	 * (ruleset->access_masks[0] is automatically upgraded to 64-bits).
> +	 */

You now can replace this comment block with that:
+	/* Checks that allowed_access matches the @ruleset constraints. */

> +	mask = landlock_get_raw_fs_access_mask(ruleset, 0);
> +	if ((path_beneath_attr.allowed_access | mask) != mask)
> +		return -EINVAL;
> +
> +	/* Gets and checks the new rule. */
> +	err = get_path_from_fd(path_beneath_attr.parent_fd, &path);
> +	if (err)
> +		return err;
> +
> +	/* Imports the new rule. */
> +	err = landlock_append_fs_rule(ruleset, &path,
> +				      path_beneath_attr.allowed_access);
> +	path_put(&path);
> +	return err;
> +}