Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH bpf-next v3 5/6] bpf: sockmap: allow update from BPF
To:     Lorenz Bauer <lmb@cloudflare.com>, <jakub@cloudflare.com>,
        <john.fastabend@gmail.com>, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>
CC:     <kernel-team@cloudflare.com>, <netdev@vger.kernel.org>,
        <bpf@vger.kernel.org>, <linux-kernel@vger.kernel.org>
References: <20200821102948.21918-1-lmb@cloudflare.com>
 <20200821102948.21918-6-lmb@cloudflare.com>
From:   Yonghong Song <yhs@fb.com>
Message-ID: <fc988cf8-e039-61f5-3d73-0ecf8f27308f@fb.com>
Date:   Fri, 21 Aug 2020 08:47:54 -0700
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0)
 Gecko/20100101 Thunderbird/68.11.0
In-Reply-To: <20200821102948.21918-6-lmb@cloudflare.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-MessageSentRepresentingType: 1
Received: from 255.255.255.255 (255.255.255.255) by BL1PR13CA0046.namprd13.prod.outlook.com (2603:10b6:208:257::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3326.10 via Frontend Transport; Fri, 21 Aug 2020 15:47:56 +0000
X-Originating-IP: [2620:10d:c091:480::1:8c09]
X-MS-PublicTrafficType: Email
X-MS-Office365-Filtering-Correlation-Id: 46dc5169-651d-49fd-4083-08d845e99413
X-MS-TrafficTypeDiagnostic: BYAPR15MB2949:
X-Microsoft-Antispam-PRVS: <BYAPR15MB2949DB3358755893D8CE3256D35B0@BYAPR15MB2949.namprd15.prod.outlook.com>
X-FB-Source: Internal
X-MS-Oob-TLC-OOBClassifiers: OLM:8882;
X-MS-Exchange-SenderADCheck: 1
X-Microsoft-Antispam: BCL:0;
X-Microsoft-Antispam-Message-Info: x76y3isM3wMC8tGV3PsqbqLmTzKCDWXI0lQKKA2yIJTcMGR6CZ2BZoMcOgxAGV0mgaeOgUvPSKPAZTbJYnx/lnQCHNcSN8kGmqx7balQDIU3HI7DX90XH4rEqCRjeOaKntIsj71DKrx+SsfTuPmf5GO+AMmR6rfvPzeZdb8cj+Tc72v8FzFXsbxQ7Yt7iPO8Id0Hxxrm0BMXVaWMu28RbehMId+Is3n8dX9ajIJQpNb1aqkcrQNFoloUI5ZbdjAn/EFWH9nzIT2JiOiiDuNG4g8kwS9vB6vfnOTyRW8Yapbo9KjGj64OU8MvYx6NFiPiRaJSn47a/itD3ThQ23sw3edn+aaGTG/va0sdeWeNAO4WwsZqcFpP1TZ17Av6lAtnM9viiZPclpXCd/GlvSM8t15BgXX6IayvMzygARQidiI=
X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BYAPR15MB4088.namprd15.prod.outlook.com;PTR:;CAT:NONE;SFS:(39860400002)(346002)(376002)(396003)(366004)(136003)(86362001)(6486002)(110011004)(316002)(31696002)(31686004)(36756003)(53546011)(478600001)(16576012)(110136005)(956004)(2616005)(186003)(52116002)(2906002)(66476007)(66946007)(66556008)(4326008)(5660300002)(15650500001)(8936002)(83380400001)(7416002)(8676002)(43740500002);DIR:OUT;SFP:1102;
X-MS-Exchange-AntiSpam-MessageData: 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
X-MS-Exchange-CrossTenant-Network-Message-Id: 46dc5169-651d-49fd-4083-08d845e99413
X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4088.namprd15.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 21 Aug 2020 15:47:58.9230
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: 1Ec4ihKwHEdwt1p8QtWLHi4AjsS46/SWZOCqzC+R+iy4Rre85llsEmOVx5GsbZdN
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2949
X-OriginatorOrg: fb.com
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687
 definitions=2020-08-21_08:2020-08-21,2020-08-21 signatures=0
X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 spamscore=0
 priorityscore=1501 suspectscore=0 clxscore=1015 bulkscore=0
 mlxlogscore=999 lowpriorityscore=0 phishscore=0 impostorscore=0
 adultscore=0 mlxscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx
 scancount=1 engine=8.12.0-2006250000 definitions=main-2008210147
X-FB-Internal: deliver
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


On 8/21/20 3:29 AM, Lorenz Bauer wrote:
> Allow calling bpf_map_update_elem on sockmap and sockhash from a BPF
> context. The synchronization required for this is a bit fiddly: we
> need to prevent the socket from changing its state while we add it
> to the sockmap, since we rely on getting a callback via
> sk_prot->unhash. However, we can't just lock_sock like in
> sock_map_sk_acquire because that might sleep. So instead we disable
> softirq processing and use bh_lock_sock to prevent further
> modification.
> 
> Yet, this is still not enough. BPF can be called in contexts where
> the current CPU might have locked a socket. If the BPF can get
> a hold of such a socket, inserting it into a sockmap would lead to
> a deadlock. One straight forward example are sock_ops programs that
> have ctx->sk, but the same problem exists for kprobes, etc.
> We deal with this by allowing sockmap updates only from known safe
> contexts. Improper usage is rejected by the verifier.
> 
> I've audited the enabled contexts to make sure they can't run in
> a locked context. It's possible that CGROUP_SKB and others are
> safe as well, but the auditing here is much more difficult. In
> any case, we can extend the safe contexts when the need arises.
> 
> Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>

Acked-by: Yonghong Song <yhs@fb.com>