linux-kernel - [PATCH] fs: Avoid signed overflow UBSAN warning

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Date:   Sat, 23 Feb 2019 17:02:10 +0800
From:   Hongbo Yao <yaohongbo@...wei.com>
To:     <viro@...iv.linux.org.uk>, <linux-fsdevel@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linuxarm@...wei.com>
Subject: [PATCH] fs: Avoid signed overflow UBSAN warning

I ran into this:
	UBSAN: Undefined behaviour in fs/read_write.c:251:11
	signed integer overflow:
	9223372036854775805 + 9223372036854775805 cannot be represented in
	type 'long long int'

Use unsigned types to do math, it doesn't throw a UBSAN warning
when it does overflow.This patch doesn't change generated code.

Signed-off-by: Hongbo Yao <yaohongbo@...wei.com>
---
 fs/read_write.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 8f08d4a2aa9a..0509e81afc8e 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -248,7 +248,7 @@ loff_t default_llseek(struct file *file, loff_t offset, int whence)
 				retval = file->f_pos;
 				goto out;
 			}
-			offset += file->f_pos;
+			offset = (u64)file->f_pos + (u64)offset;
 			break;
 		case SEEK_DATA:
 			/*
-- 
2.20.1