linux-kernel - [PATCH v2] ksmbd: vfs_cache: avoid integer overflow in inode

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Message-Id: <20251115144836.555128-1-pioooooooooip@gmail.com>
Date: Sat, 15 Nov 2025 23:48:36 +0900
From: Qianchang Zhao <pioooooooooip@...il.com>
To: Namjae Jeon <linkinjeon@...nel.org>,
	Steve French <smfrench@...il.com>
Cc: gregkh@...uxfoundation.org,
	linux-cifs@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Zhitong Liu <liuzhitong1993@...il.com>,
	Qianchang Zhao <pioooooooooip@...il.com>,
	stable@...r.kernel.org
Subject: [PATCH v2] ksmbd: vfs_cache: avoid integer overflow in inode_hash()

inode_hash() currently mixes a hash value with the super_block pointer
using an unbounded multiplication:

    tmp = (hashval * (unsigned long)sb) ^
          (GOLDEN_RATIO_PRIME + hashval) / L1_CACHE_BYTES;

On 64-bit kernels this multiplication can overflow and wrap in unsigned
long arithmetic. While this is not a memory-safety issue, it is an
unbounded integer operation and weakens the mixing properties of the
hash.

Replace the pointer*hash multiply with hash_long() over a mixed value
(hashval ^ (unsigned long)sb) and keep the existing shift/mask. This
removes the overflow source and reuses the standard hash helper already
used in other kernel code.

This is an integer wraparound / robustness issue (CWE-190/CWE-407),
not a memory-safety bug.

Reported-by: Qianchang Zhao <pioooooooooip@...il.com>
Reported-by: Zhitong Liu <liuzhitong1993@...il.com>
Cc: stable@...r.kernel.org
Signed-off-by: Qianchang Zhao <pioooooooooip@...il.com>
---
 fs/smb/server/vfs_cache.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/fs/smb/server/vfs_cache.c b/fs/smb/server/vfs_cache.c
index dfed6fce8..a62ea5aae 100644
--- a/fs/smb/server/vfs_cache.c
+++ b/fs/smb/server/vfs_cache.c
@@ -10,6 +10,7 @@
 #include <linux/vmalloc.h>
 #include <linux/kthread.h>
 #include <linux/freezer.h>
+#include <linux/hash.h>
 
 #include "glob.h"
 #include "vfs_cache.h"
@@ -65,12 +66,8 @@ static void fd_limit_close(void)
 
 static unsigned long inode_hash(struct super_block *sb, unsigned long hashval)
 {
-	unsigned long tmp;
-
-	tmp = (hashval * (unsigned long)sb) ^ (GOLDEN_RATIO_PRIME + hashval) /
-		L1_CACHE_BYTES;
-	tmp = tmp ^ ((tmp ^ GOLDEN_RATIO_PRIME) >> inode_hash_shift);
-	return tmp & inode_hash_mask;
+	unsigned long mixed = hashval ^ (unsigned long)sb;
+	return hash_long(mixed, inode_hash_shift) & inode_hash_mask;
 }
 
 static struct ksmbd_inode *__ksmbd_inode_lookup(struct dentry *de)
-- 
2.34.1