linux-kernel - [PATCH] btrfs: qgroup: delete unnecessary check in btrfs_qgroup_check

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Message-ID: <cb21ce67-e9d8-4844-8c70-eb42f6ac4aee@moroto.mountain>
Date: Thu, 7 Mar 2024 17:53:47 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Chris Mason <clm@...com>, Qu Wenruo <wqu@...e.com>
Cc: Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: [PATCH] btrfs: qgroup: delete unnecessary check in
 btrfs_qgroup_check_inherit()

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@...aro.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