Re: [PATCH v1 4/4] landlock: Use scoped guards for mutex

["Günther Noack" <gnoack@google.com>]

On Mon, Jan 13, 2025 at 05:11:12PM +0100, Mickaël Salaün wrote:
> Simplify error handling by replacing goto statements with automatic
> calls to mutex_unlock() when going out of scope.
> 
> Do not initialize the err variable for compiler/linter to warn us about
> inconsistent use, if any.
> 
> Cc: Boqun Feng <boqun.feng@gmail.com>
> Cc: Günther Noack <gnoack@google.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Will Deacon <will@kernel.org>
> Signed-off-by: Mickaël Salaün <mic@digikod.net>
> Link: https://lore.kernel.org/r/20250113161112.452505-5-mic@digikod.net
> ---
>  security/landlock/ruleset.c | 52 +++++++++++++++----------------------
>  1 file changed, 21 insertions(+), 31 deletions(-)
> 
> diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
> index f27b7bdb19b9..f1c3104aea6c 100644
> --- a/security/landlock/ruleset.c
> +++ b/security/landlock/ruleset.c
> @@ -367,7 +367,7 @@ static int merge_tree(struct landlock_ruleset *const dst,
>  static int merge_ruleset(struct landlock_ruleset *const dst,
>  			 struct landlock_ruleset *const src)
>  {
> -	int err = 0;
> +	int err;
>  
>  	might_sleep();
>  	/* Should already be checked by landlock_merge_ruleset() */
> @@ -378,32 +378,28 @@ static int merge_ruleset(struct landlock_ruleset *const dst,
>  		return -EINVAL;
>  
>  	/* Locks @dst first because we are its only owner. */
> -	mutex_lock(&dst->lock);
> -	mutex_lock_nested(&src->lock, SINGLE_DEPTH_NESTING);
> +	guard(mutex)(&dst->lock);
> +	guard(mutex_nest_1)(&src->lock);
>  
>  	/* Stacks the new layer. */
> -	if (WARN_ON_ONCE(src->num_layers != 1 || dst->num_layers < 1)) {
> -		err = -EINVAL;
> -		goto out_unlock;
> -	}
> +	if (WARN_ON_ONCE(src->num_layers != 1 || dst->num_layers < 1))
> +		return -EINVAL;
> +
>  	dst->access_masks[dst->num_layers - 1] = src->access_masks[0];
>  
>  	/* Merges the @src inode tree. */
>  	err = merge_tree(dst, src, LANDLOCK_KEY_INODE);
>  	if (err)
> -		goto out_unlock;
> +		return err;
>  
>  #if IS_ENABLED(CONFIG_INET)
>  	/* Merges the @src network port tree. */
>  	err = merge_tree(dst, src, LANDLOCK_KEY_NET_PORT);
>  	if (err)
> -		goto out_unlock;
> +		return err;
>  #endif /* IS_ENABLED(CONFIG_INET) */
>  
> -out_unlock:
> -	mutex_unlock(&src->lock);
> -	mutex_unlock(&dst->lock);
> -	return err;
> +	return 0;
>  }
>  
>  static int inherit_tree(struct landlock_ruleset *const parent,
> @@ -441,47 +437,41 @@ static int inherit_tree(struct landlock_ruleset *const parent,
>  static int inherit_ruleset(struct landlock_ruleset *const parent,
>  			   struct landlock_ruleset *const child)
>  {
> -	int err = 0;
> +	int err;
>  
>  	might_sleep();
>  	if (!parent)
>  		return 0;
>  
>  	/* Locks @child first because we are its only owner. */
> -	mutex_lock(&child->lock);
> -	mutex_lock_nested(&parent->lock, SINGLE_DEPTH_NESTING);
> +	guard(mutex)(&child->lock);
> +	guard(mutex_nest_1)(&parent->lock);
>  
>  	/* Copies the @parent inode tree. */
>  	err = inherit_tree(parent, child, LANDLOCK_KEY_INODE);
>  	if (err)
> -		goto out_unlock;
> +		return err;
>  
>  #if IS_ENABLED(CONFIG_INET)
>  	/* Copies the @parent network port tree. */
>  	err = inherit_tree(parent, child, LANDLOCK_KEY_NET_PORT);
>  	if (err)
> -		goto out_unlock;
> +		return err;
>  #endif /* IS_ENABLED(CONFIG_INET) */
>  
> -	if (WARN_ON_ONCE(child->num_layers <= parent->num_layers)) {
> -		err = -EINVAL;
> -		goto out_unlock;
> -	}
> +	if (WARN_ON_ONCE(child->num_layers <= parent->num_layers))
> +		return -EINVAL;
> +
>  	/* Copies the parent layer stack and leaves a space for the new layer. */
>  	memcpy(child->access_masks, parent->access_masks,
>  	       flex_array_size(parent, access_masks, parent->num_layers));
>  
> -	if (WARN_ON_ONCE(!parent->hierarchy)) {
> -		err = -EINVAL;
> -		goto out_unlock;
> -	}
> +	if (WARN_ON_ONCE(!parent->hierarchy))
> +		return -EINVAL;
> +
>  	get_hierarchy(parent->hierarchy);
>  	child->hierarchy->parent = parent->hierarchy;
> -
> -out_unlock:
> -	mutex_unlock(&parent->lock);
> -	mutex_unlock(&child->lock);
> -	return err;
> +	return 0;
>  }
>  
>  static void free_ruleset(struct landlock_ruleset *const ruleset)
> -- 
> 2.47.1
> 

Reviewed-by: Günther Noack <gnoack@google.com>

(Assuming that the mutex_nest_1 guard from the previous commit is OK as well)

—Günther