linux-kernel - [PATCH v2 2/2] fs: clear a UBSAN shift-out-of-bounds warning

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Date:   Mon, 21 Nov 2022 10:44:18 +0800
From:   Zhen Lei <thunder.leizhen@...wei.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Eric Biggers <ebiggers@...nel.org>,
        <linux-fsdevel@...r.kernel.org>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, <linux-btrfs@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     Zhen Lei <thunder.leizhen@...wei.com>
Subject: [PATCH v2 2/2] 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 type_max() 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

Suggested-by: Eric Biggers <ebiggers@...nel.org>
Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
---
 include/linux/fs.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index e654435f16512c1..a384741b1449457 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1131,9 +1131,8 @@ 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 OFFSET_MAX	INT_LIMIT(loff_t)
-#define OFFT_OFFSET_MAX	INT_LIMIT(off_t)
+#define OFFSET_MAX	type_max(loff_t)
+#define OFFT_OFFSET_MAX	type_max(off_t)
 #endif
 
 extern void send_sigio(struct fown_struct *fown, int fd, int band);
-- 
2.25.1