Re: [PATCH] btrfs: qgroup: delete unnecessary check in btrfs_qgroup_check_inherit()

From: Qu Wenruo
Date: Thu Mar 07 2024 - 14:38:15 EST




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@xxxxxxxxxx>

Reviewed-by: Qu Wenruo <wqu@xxxxxxxx>

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;