From a718e28f538441a3b6612da9ff226973376cdf0f Mon Sep 17 00:00:00 2001 From: Andrey Ryabinin <aryabinin@virtuozzo.com> Date: Fri, 17 Aug 2018 15:46:57 -0700 Subject: [PATCH] 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> --- mm/fadvise.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/mm/fadvise.c b/mm/fadvise.c index afa41491d324..2d8376e3c640 100644 --- a/mm/fadvise.c +++ b/mm/fadvise.c @@ -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