Commit a718e28f authored Aug 17, 2018 by Andrey Ryabinin Committed by Linus Torvalds Aug 17, 2018

mm/fadvise.c: fix signed overflow UBSAN complaint

Signed integer overflow is undefined according to the C standard.  The
overflow in ksys_fadvise64_64() is deliberate, but since it is signed
overflow, UBSAN complains:

	UBSAN: Undefined behaviour in mm/fadvise.c:76:10
	signed integer overflow:
	4 + 9223372036854775805 cannot be represented in type 'long long int'

Use unsigned types to do math.  Unsigned overflow is defined so UBSAN
will not complain about it.  This patch doesn't change generated code.

[akpm@linux-foundation.org: add comment explaining the casts]
Link: http://lkml.kernel.org/r/20180629184453.7614-1-aryabinin@virtuozzo.com


Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reported-by:  <icytxw@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 31f21da1

mm/fadvise.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -72,8 +72,12 @@ int ksys_fadvise64_64(int fd, loff_t offset, loff_t len, int advice)
		goto out;
		}

		/* Careful about overflows. Len == 0 means "as much as possible" */
		endbyte = offset + len;
		/*
		* Careful about overflows. Len == 0 means "as much as possible". Use
		* unsigned math because signed overflows are undefined and UBSan
		* complains.
		*/
		endbyte = (u64)offset + (u64)len;
		if (!len \|\| endbyte < len)
		endbyte = -1;
		else

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