linux-kernel - [PATCH] fs: Clear a UBSAN shift-out-of-bounds warning

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Message-ID: <20221110031024.204-1-thunder.leizhen@huawei.com>
Date:   Thu, 10 Nov 2022 11:10:24 +0800
From:   Zhen Lei <thunder.leizhen@...wei.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     Zhen Lei <thunder.leizhen@...wei.com>
Subject: [PATCH] fs: Clear a UBSAN shift-out-of-bounds warning

UBSAN: shift-out-of-bounds in fs/locks.c:2572:16
left shift of 1 by 63 places cannot be represented in type 'long long int'

Switch the calculation method to ((quarter - 1) * 2 + 1) can help us
eliminate this false positive.

On the other hand, the old implementation has problems with char and
short types, although not currently involved.
printf("%d: %x\n", sizeof(char),  INT_LIMIT(char));
printf("%d: %x\n", sizeof(short), INT_LIMIT(short));
1: ffffff7f
2: ffff7fff

Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
---
 include/linux/fs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index e654435f16512c1..88d42e2daed9f6c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1131,7 +1131,7 @@ struct file_lock_context {
 
 /* The following constant reflects the upper bound of the file/locking space */
 #ifndef OFFSET_MAX
-#define INT_LIMIT(x)	(~((x)1 << (sizeof(x)*8 - 1)))
+#define INT_LIMIT(x)	((((x)1 << (sizeof(x) * 8 - 2)) - 1) * 2  + 1)
 #define OFFSET_MAX	INT_LIMIT(loff_t)
 #define OFFT_OFFSET_MAX	INT_LIMIT(off_t)
 #endif
-- 
2.25.1