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Miller" , Sasha Levin Subject: [PATCH AUTOSEL for 4.9 066/219] tcp: sysctl: Fix a race to avoid unexpected 0 window from space Thread-Topic: [PATCH AUTOSEL for 4.9 066/219] tcp: sysctl: Fix a race to avoid unexpected 0 window from space Thread-Index: AQHTsz73/P0X5bkOO0KFo9zMB2xmUQ== Date: Sat, 3 Mar 2018 22:28:34 +0000 Message-ID: <20180303222716.26640-66-alexander.levin@microsoft.com> References: <20180303222716.26640-1-alexander.levin@microsoft.com> In-Reply-To: <20180303222716.26640-1-alexander.levin@microsoft.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [52.168.54.252] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1;MW2PR2101MB1098;7:+69PQ6AJIDXg6Nx7KYeNddUrXwn4dhscZ2Q91VKewQ6R+UhPul4/1StzxrEh+ymvVkTYsg0P1ss9jjzaYW8P63udLRnrLo2lpaHLj7IDCGnCI/smkZkvOEKRSefzmf6d+K/W2p+4zkBJR+4DBv2FGmyHT1mk3qIaFF3yU4Y0chnKrVydHahcqVXjUH5QZa4UW1uw+fQbx5stZ+r/LvwXRXj63PWVdEfj43zqYSUYo+q27QBJLFHiElZKW8HRuXBJ x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: d03ba52e-f34e-4b63-d0b9-08d58156b336 x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(4534165)(4627221)(201703031133081)(201702281549075)(48565401081)(5600026)(4604075)(3008032)(2017052603307)(7193020);SRVR:MW2PR2101MB1098; x-ms-traffictypediagnostic: MW2PR2101MB1098: authentication-results: spf=none (sender IP is ) smtp.mailfrom=Alexander.Levin@microsoft.com; x-microsoft-antispam-prvs: x-exchange-antispam-report-test: UriScan:(28532068793085)(89211679590171); x-exchange-antispam-report-cfa-test: BCL:0;PCL:0;RULEID:(8211001083)(61425038)(6040501)(2401047)(5005006)(8121501046)(3231220)(944501244)(52105095)(10201501046)(3002001)(93006095)(93001095)(6055026)(61426038)(61427038)(6041288)(20161123562045)(20161123564045)(20161123558120)(20161123560045)(201703131423095)(201702281528075)(20161123555045)(201703061421075)(201703061406153)(6072148)(201708071742011);SRVR:MW2PR2101MB1098;BCL:0;PCL:0;RULEID:;SRVR:MW2PR2101MB1098; x-forefront-prvs: 0600F93FE1 x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(39860400002)(376002)(39380400002)(366004)(396003)(346002)(199004)(189003)(2906002)(8936002)(36756003)(6512007)(81156014)(10290500003)(81166006)(99286004)(6436002)(68736007)(478600001)(3846002)(22452003)(53936002)(8676002)(110136005)(54906003)(4326008)(316002)(76176011)(6116002)(7736002)(105586002)(305945005)(3660700001)(1076002)(14454004)(97736004)(575784001)(25786009)(186003)(72206003)(26005)(102836004)(86362001)(6666003)(2501003)(3280700002)(6506007)(5660300001)(10090500001)(66066001)(106356001)(5250100002)(2900100001)(2950100002)(86612001)(6486002)(107886003)(22906009)(217873001);DIR:OUT;SFP:1102;SCL:1;SRVR:MW2PR2101MB1098;H:MW2PR2101MB1034.namprd21.prod.outlook.com;FPR:;SPF:None;PTR:InfoNoRecords;A:1;MX:1;LANG:en; x-microsoft-antispam-message-info: mHjOcu/qBTu1LKyOzi9E8KHraqgjeICS44iGM2EJZKiV2L2/SCYHyhhrzAQ+uI3iQFtEMQfgq14TQqAmAJJDgodO4/Vc8ZqSb9tVpKniYSh29/1FiGezlMjgTrwb/bk4TC6J563sfVIYF8BhFv86A4vqMVDbMKMNhp1OpuSu3Go= spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-Network-Message-Id: d03ba52e-f34e-4b63-d0b9-08d58156b336 X-MS-Exchange-CrossTenant-originalarrivaltime: 03 Mar 2018 22:28:34.5256 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW2PR2101MB1098 Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: From: Gao Feng [ Upstream commit c48367427a39ea0b85c7cf018fe4256627abfd9e ] Because sysctl_tcp_adv_win_scale could be changed any time, so there is one race in tcp_win_from_space. For example, 1.sysctl_tcp_adv_win_scale<=3D0 (sysctl_tcp_adv_win_scale is negative now) 2.space>>(-sysctl_tcp_adv_win_scale) (sysctl_tcp_adv_win_scale is postive n= ow) As a result, tcp_win_from_space returns 0. It is unexpected. Certainly if the compiler put the sysctl_tcp_adv_win_scale into one register firstly, then use the register directly, it would be ok. But we could not depend on the compiler behavior. Signed-off-by: Gao Feng Signed-off-by: David S. Miller Signed-off-by: Sasha Levin --- include/net/tcp.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index caf35e062639..18f029bcb8c7 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1265,9 +1265,11 @@ void tcp_select_initial_window(int __space, __u32 ms= s, __u32 *rcv_wnd, =20 static inline int tcp_win_from_space(int space) { - return sysctl_tcp_adv_win_scale<=3D0 ? - (space>>(-sysctl_tcp_adv_win_scale)) : - space - (space>>sysctl_tcp_adv_win_scale); + int tcp_adv_win_scale =3D sysctl_tcp_adv_win_scale; + + return tcp_adv_win_scale <=3D 0 ? + (space>>(-tcp_adv_win_scale)) : + space - (space>>tcp_adv_win_scale); } =20 /* Note: caller must be prepared to deal with negative returns */ --=20 2.14.1