From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Stanislaw Gruszka <sgruszka@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Sasha Levin <sashal@kernel.org>
Subject: [PATCH AUTOSEL 3.18 09/10] lib/div64.c: off by one in shift
Date: Fri, 29 Mar 2019 21:32:26 -0400 [thread overview]
Message-ID: <20190330013227.1365-9-sashal@kernel.org> (raw)
In-Reply-To: <20190330013227.1365-1-sashal@kernel.org>
From: Stanislaw Gruszka <sgruszka@redhat.com>
[ Upstream commit cdc94a37493135e355dfc0b0e086d84e3eadb50d ]
fls counts bits starting from 1 to 32 (returns 0 for zero argument). If
we add 1 we shift right one bit more and loose precision from divisor,
what cause function incorect results with some numbers.
Corrected code was tested in user-space, see bugzilla:
https://bugzilla.kernel.org/show_bug.cgi?id=202391
Link: http://lkml.kernel.org/r/1548686944-11891-1-git-send-email-sgruszka@redhat.com
Fixes: 658716d19f8f ("div64_u64(): improve precision on 32bit platforms")
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Reported-by: Siarhei Volkau <lis8215@gmail.com>
Tested-by: Siarhei Volkau <lis8215@gmail.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
lib/div64.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/lib/div64.c b/lib/div64.c
index 4382ad77777e..ce76dc3d674e 100644
--- a/lib/div64.c
+++ b/lib/div64.c
@@ -100,7 +100,7 @@ u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
quot = div_u64_rem(dividend, divisor, &rem32);
*remainder = rem32;
} else {
- int n = 1 + fls(high);
+ int n = fls(high);
quot = div_u64(dividend >> n, divisor >> n);
if (quot != 0)
@@ -138,7 +138,7 @@ u64 div64_u64(u64 dividend, u64 divisor)
if (high == 0) {
quot = div_u64(dividend, divisor);
} else {
- int n = 1 + fls(high);
+ int n = fls(high);
quot = div_u64(dividend >> n, divisor >> n);
if (quot != 0)
--
2.19.1
next prev parent reply other threads:[~2019-03-30 1:33 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-30 1:32 [PATCH AUTOSEL 3.18 01/10] rsi: improve kernel thread handling to fix kernel panic Sasha Levin
2019-03-30 1:32 ` [PATCH AUTOSEL 3.18 02/10] 9p: do not trust pdu content for stat item size Sasha Levin
2019-03-30 1:32 ` [PATCH AUTOSEL 3.18 03/10] 9p locks: add mount option for lock retry interval Sasha Levin
2019-03-30 1:32 ` [PATCH AUTOSEL 3.18 04/10] serial: uartps: console_setup() can't be placed to init section Sasha Levin
2019-03-30 1:32 ` [PATCH AUTOSEL 3.18 05/10] ARM: samsung: Limit SAMSUNG_PM_CHECK config option to non-Exynos platforms Sasha Levin
2019-03-30 1:32 ` [PATCH AUTOSEL 3.18 06/10] ACPI / SBS: Fix GPE storm on recent MacBookPro's Sasha Levin
2019-03-30 1:32 ` [PATCH AUTOSEL 3.18 07/10] iommu/dmar: Fix buffer overflow during PCI bus notification Sasha Levin
2019-03-30 1:32 ` [PATCH AUTOSEL 3.18 08/10] appletalk: Fix use-after-free in atalk_proc_exit Sasha Levin
2019-03-30 1:32 ` Sasha Levin [this message]
2019-03-30 1:32 ` [PATCH AUTOSEL 3.18 10/10] include/linux/swap.h: use offsetof() instead of custom __swapoffset macro Sasha Levin
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