linux-ext4 - [PATCH v2 02/10] ext4: avoid potential data overflow in next_linear

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Date:   Wed, 26 Jul 2023 02:50:58 +0800
From:   Kemeng Shi <shikemeng@...weicloud.com>
To:     tytso@....edu, adilger.kernel@...ger.ca, ritesh.list@...il.com,
        ojaswin@...ux.ibm.com, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     shikemeng@...weicloud.com
Subject: [PATCH v2 02/10] ext4: avoid potential data overflow in next_linear_group

ngroups is ext4_group_t (unsigned int) while next_linear_group treat it
in int. If ngroups is bigger than max number described by int, it will
be treat as a negative number. Then "return group + 1 >= ngroups ? 0 :
group + 1;" may keep returning 0.
Switch int to ext4_group_t in next_linear_group to fix the overflow.

Fixes: 196e402adf2e ("ext4: improve cr 0 / cr 1 group scanning")
Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
---
 fs/ext4/mballoc.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 62e7a045ad79..3cd795e98008 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1080,8 +1080,9 @@ static inline int should_optimize_scan(struct ext4_allocation_context *ac)
  * Return next linear group for allocation. If linear traversal should not be
  * performed, this function just returns the same group
  */
-static int
-next_linear_group(struct ext4_allocation_context *ac, int group, int ngroups)
+static ext4_group_t
+next_linear_group(struct ext4_allocation_context *ac, ext4_group_t group,
+		  ext4_group_t ngroups)
 {
 	if (!should_optimize_scan(ac))
 		goto inc_and_return;
-- 
2.30.0