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 4.9 20/21] lib/div64.c: off by one in shift
Date: Fri, 29 Mar 2019 21:31:11 -0400 [thread overview]
Message-ID: <20190330013112.784-20-sashal@kernel.org> (raw)
In-Reply-To: <20190330013112.784-1-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 7f345259c32f..c1c1a4c36dd5 100644
--- a/lib/div64.c
+++ b/lib/div64.c
@@ -102,7 +102,7 @@ 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)
@@ -140,7 +140,7 @@ 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 1:35 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-30 1:30 [PATCH AUTOSEL 4.9 01/21] gpio: pxa: handle corner case of unprobed device Sasha Levin
2019-03-30 1:30 ` [PATCH AUTOSEL 4.9 02/21] rsi: improve kernel thread handling to fix kernel panic Sasha Levin
2019-03-30 1:30 ` [PATCH AUTOSEL 4.9 03/21] 9p: do not trust pdu content for stat item size Sasha Levin
2019-03-30 1:30 ` [PATCH AUTOSEL 4.9 04/21] 9p locks: add mount option for lock retry interval Sasha Levin
2019-03-30 1:30 ` [PATCH AUTOSEL 4.9 05/21] f2fs: fix to do sanity check with current segment number Sasha Levin
2019-03-30 1:30 ` [PATCH AUTOSEL 4.9 06/21] serial: uartps: console_setup() can't be placed to init section Sasha Levin
2019-03-30 1:30 ` [PATCH AUTOSEL 4.9 07/21] HID: i2c-hid: override HID descriptors for certain devices Sasha Levin
2019-03-30 1:30 ` [PATCH AUTOSEL 4.9 08/21] ARM: samsung: Limit SAMSUNG_PM_CHECK config option to non-Exynos platforms Sasha Levin
2019-03-30 1:31 ` [PATCH AUTOSEL 4.9 09/21] ACPI / SBS: Fix GPE storm on recent MacBookPro's Sasha Levin
2019-03-30 1:31 ` [PATCH AUTOSEL 4.9 10/21] cifs: fallback to older infolevels on findfirst queryinfo retry Sasha Levin
2019-03-30 1:31 ` [PATCH AUTOSEL 4.9 11/21] kernel: hung_task.c: disable on suspend Sasha Levin
2019-03-30 1:31 ` [PATCH AUTOSEL 4.9 12/21] crypto: sha256/arm - fix crash bug in Thumb2 build Sasha Levin
2019-03-30 1:31 ` [PATCH AUTOSEL 4.9 13/21] crypto: sha512/arm " Sasha Levin
2019-03-30 1:31 ` [PATCH AUTOSEL 4.9 14/21] iommu/dmar: Fix buffer overflow during PCI bus notification Sasha Levin
2019-03-30 1:31 ` [PATCH AUTOSEL 4.9 15/21] soc/tegra: pmc: Drop locking from tegra_powergate_is_powered() Sasha Levin
2019-03-30 1:31 ` [PATCH AUTOSEL 4.9 16/21] ext4: prohibit fstrim in norecovery mode Sasha Levin
2019-03-30 1:31 ` [PATCH AUTOSEL 4.9 17/21] lkdtm: Add tests for NULL pointer dereference Sasha Levin
2019-03-30 1:31 ` [PATCH AUTOSEL 4.9 18/21] ARM: 8839/1: kprobe: make patch_lock a raw_spinlock_t Sasha Levin
2019-03-30 1:31 ` [PATCH AUTOSEL 4.9 19/21] appletalk: Fix use-after-free in atalk_proc_exit Sasha Levin
2019-03-30 1:31 ` Sasha Levin [this message]
2019-03-30 1:31 ` [PATCH AUTOSEL 4.9 21/21] include/linux/swap.h: use offsetof() instead of custom __swapoffset macro Sasha Levin
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