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mm/fadvise.c: fix signed overflow UBSAN complaint

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[ Upstream commit a718e28f53 ]

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>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Andrey Ryabinin 2018-08-17 15:46:57 -07:00 committed by Greg Kroah-Hartman
parent 2dc61587a1
commit 4570403f6e
1 changed files with 6 additions and 2 deletions
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8
mm/fadvise.c
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@ -71,8 +71,12 @@ SYSCALL_DEFINE4(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