This check "if (inherit->num_qgroups > PAGE_SIZE)" is confusing and
unnecessary.

The problem with the check is that static checkers flag it as a
potential mixup of between units of bytes vs number of elements.
Fortunately, the check can safely be deleted because the next check is
correct and applies an even stricter limit:

	if (size != struct_size(inherit, qgroups, inherit->num_qgroups))
		return -EINVAL;

The "inherit" struct ends in a variable array of __u64 and
"inherit->num_qgroups" is the number of elements in the array.  At the
start of the function we check that:

	if (size < sizeof(*inherit) || size > PAGE_SIZE)
		return -EINVAL;

Thus, since we verify that the whole struct fits within one page, that
means that the number of elements in the inherit->qgroups[] array must
be less than PAGE_SIZE.

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
---
 fs/btrfs/qgroup.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 5f90f0605b12..a8197e25192c 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -3067,9 +3067,6 @@ int btrfs_qgroup_check_inherit(struct btrfs_fs_info *fs_info,
 	if (inherit->num_ref_copies > 0 || inherit->num_excl_copies > 0)
 		return -EINVAL;
 
-	if (inherit->num_qgroups > PAGE_SIZE)
-		return -EINVAL;
-
 	if (size != struct_size(inherit, qgroups, inherit->num_qgroups))
 		return -EINVAL;
 
-- 
2.43.0

On Thu, Mar 07, 2024 at 05:53:47PM +0300, Dan Carpenter wrote:
> This check "if (inherit->num_qgroups > PAGE_SIZE)" is confusing and
> unnecessary.
> 
> The problem with the check is that static checkers flag it as a
> potential mixup of between units of bytes vs number of elements.
> Fortunately, the check can safely be deleted because the next check is
> correct and applies an even stricter limit:
> 
> 	if (size != struct_size(inherit, qgroups, inherit->num_qgroups))
> 		return -EINVAL;
> 
> The "inherit" struct ends in a variable array of __u64 and
> "inherit->num_qgroups" is the number of elements in the array.  At the
> start of the function we check that:
> 
> 	if (size < sizeof(*inherit) || size > PAGE_SIZE)
> 		return -EINVAL;
> 
> Thus, since we verify that the whole struct fits within one page, that
> means that the number of elements in the inherit->qgroups[] array must
> be less than PAGE_SIZE.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>

Added to for-next, thanks.

在 2024/3/8 01:23, Dan Carpenter 写道:
> This check "if (inherit->num_qgroups > PAGE_SIZE)" is confusing and
> unnecessary.
>
> The problem with the check is that static checkers flag it as a
> potential mixup of between units of bytes vs number of elements.
> Fortunately, the check can safely be deleted because the next check is
> correct and applies an even stricter limit:
>
> 	if (size != struct_size(inherit, qgroups, inherit->num_qgroups))
> 		return -EINVAL;
>
> The "inherit" struct ends in a variable array of __u64 and
> "inherit->num_qgroups" is the number of elements in the array.  At the
> start of the function we check that:
>
> 	if (size < sizeof(*inherit) || size > PAGE_SIZE)
> 		return -EINVAL;
>
> Thus, since we verify that the whole struct fits within one page, that
> means that the number of elements in the inherit->qgroups[] array must
> be less than PAGE_SIZE.
>
> Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>

Reviewed-by: Qu Wenruo <wqu@suse.com>

I'm not 100% sure about the original code either, thanks for confirming
the existing one has no effect and can be removed.

Thanks,
Qu
> ---
>   fs/btrfs/qgroup.c | 3 ---
>   1 file changed, 3 deletions(-)
>
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index 5f90f0605b12..a8197e25192c 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -3067,9 +3067,6 @@ int btrfs_qgroup_check_inherit(struct btrfs_fs_info *fs_info,
>   	if (inherit->num_ref_copies > 0 || inherit->num_excl_copies > 0)
>   		return -EINVAL;
>
> -	if (inherit->num_qgroups > PAGE_SIZE)
> -		return -EINVAL;
> -
>   	if (size != struct_size(inherit, qgroups, inherit->num_qgroups))
>   		return -EINVAL;
>