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Thu, 9 Jul 2020 18:47:31 +0000 Date: Thu, 9 Jul 2020 11:47:29 -0700 From: Martin KaFai Lau To: James Chapman CC: , Alexei Starovoitov , Daniel Borkmann , , Subject: Re: [PATCH v2 bpf 2/2] bpf: net: Avoid incorrect bpf_sk_reuseport_detach call Message-ID: <20200709184729.jg2y2g6crxlazlqo@kafai-mbp> References: <20200709061057.4018499-1-kafai@fb.com> <20200709061110.4019316-1-kafai@fb.com> <20200709105833.GA1761@katalix.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200709105833.GA1761@katalix.com> User-Agent: NeoMutt/20180716 X-ClientProxiedBy: BYAPR05CA0086.namprd05.prod.outlook.com (2603:10b6:a03:e0::27) To BY5PR15MB3571.namprd15.prod.outlook.com (2603:10b6:a03:1f6::32) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from kafai-mbp (2620:10d:c090:400::5:7541) by BYAPR05CA0086.namprd05.prod.outlook.com (2603:10b6:a03:e0::27) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3195.10 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 294b2dee-fee6-4a87-007b-08d8243888bf X-MS-Exchange-CrossTenant-AuthSource: BY5PR15MB3571.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Jul 2020 18:47:30.8449 (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: TpTXyOecHgoUIY50Msy1KCxqeWiRoffECrbc7d7qgxwjQmRZpXN4FuEi4gqMGnX2 X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2567 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-07-09_10:2020-07-09,2020-07-09 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 malwarescore=0 adultscore=0 mlxscore=0 suspectscore=0 priorityscore=1501 clxscore=1015 bulkscore=0 phishscore=0 spamscore=0 mlxlogscore=999 lowpriorityscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2007090129 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Thu, Jul 09, 2020 at 11:58:33AM +0100, James Chapman wrote: > On Wed, Jul 08, 2020 at 23:11:10 -0700, Martin KaFai Lau wrote: > > bpf_sk_reuseport_detach is currently called when sk->sk_user_data > > is not NULL. It is incorrect because sk->sk_user_data may not be > > managed by the bpf's reuseport_array. It has been reported in [1] that, > > the bpf_sk_reuseport_detach() which is called from udp_lib_unhash() has > > corrupted the sk_user_data managed by l2tp. > > > > This patch solves it by using another bit (defined as SK_USER_DATA_BPF) > > of the sk_user_data pointer value. It marks that a sk_user_data is > > managed/owned by BPF. > > I have reservations about using a bit in sk_user_data to indicate > ownership of that pointer. But putting that aside, I confirm that the > patch fixes the problem. > > Acked-by: James Chapman > Tested-by: James Chapman > Reported-by: syzbot+9f092552ba9a5efca5df@syzkaller.appspotmail.com Thanks for the test! One bit of sk_user_data has already been used to indicate SK_USER_DATA_NOCOPY. I think using another bit is the cleanest fix for the bpf/net branch instead of tracking this somewhere else.