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Sat, 3 Feb 2018 13:28:49 -0500 Received: from mail-bl2nam02on0127.outbound.protection.outlook.com ([104.47.38.127]:37417 "EHLO NAM02-BL2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752688AbeBCSEr (ORCPT ); Sat, 3 Feb 2018 13:04:47 -0500 From: Sasha Levin To: "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" CC: John Fastabend , Daniel Borkmann , Sasha Levin Subject: [PATCH AUTOSEL for 4.14 093/110] bpf: sockmap missing NULL psock check Thread-Topic: [PATCH AUTOSEL for 4.14 093/110] bpf: sockmap missing NULL psock check Thread-Index: AQHTnRkDvCnymrbU0Uqy41wVbJxB9g== Date: Sat, 3 Feb 2018 18:01:27 +0000 Message-ID: <20180203180015.29073-93-alexander.levin@microsoft.com> References: <20180203180015.29073-1-alexander.levin@microsoft.com> In-Reply-To: <20180203180015.29073-1-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;BL0PR2101MB1041;7:lWvcmvqftcy3H0vki5Efkvb2iDs8Yu+g+KbaTUtH1TvS7HBwJm5ME9V1Sfo/KraY1UH51UTkDBsOfe1l0kSnaDmuMH8mKxhzRGsWFQF/obxiLTE/NDxGuV4XqgXPnIGd1YY8lRPlpQgoPjTKQVOx7HCej9a/Dbw9LYr5meM2++k7FFAIJduQECj9yrePkDdsLN5KKt9LnHL7at35PTQZocQq+EB9bfIwc6i9c3VjC3ZJOKCofc+6cUA71O/JfvqP x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: efb4e84d-eeea-45e2-53f5-08d56b30554e x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(48565401081)(4534165)(4627221)(201703031133081)(201702281549075)(5600026)(4604075)(3008032)(2017052603307)(7193020);SRVR:BL0PR2101MB1041; 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authentication-results: spf=none (sender IP is ) smtp.mailfrom=Alexander.Levin@microsoft.com; x-microsoft-antispam-message-info: 43N+CTZr9g3yl9Tpt9dIsJPIUw6O35M28gvB0ADmTGVht+XM2Cghc5hY2kdD6VEKAvRJz9raT5dtB5F4vCq38g== 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: efb4e84d-eeea-45e2-53f5-08d56b30554e X-MS-Exchange-CrossTenant-originalarrivaltime: 03 Feb 2018 18:01:27.7690 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL0PR2101MB1041 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: John Fastabend [ Upstream commit 5731a879d03bdaa00265f8ebc32dfd0e65d25276 ] Add psock NULL check to handle a racing sock event that can get the sk_callback_lock before this case but after xchg happens causing the refcnt to hit zero and sock user data (psock) to be null and queued for garbage collection. Also add a comment in the code because this is a bit subtle and not obvious in my opinion. Signed-off-by: John Fastabend Signed-off-by: Daniel Borkmann Signed-off-by: Sasha Levin --- kernel/bpf/sockmap.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c index dbd7b322a86b..1890be7ea9cd 100644 --- a/kernel/bpf/sockmap.c +++ b/kernel/bpf/sockmap.c @@ -588,8 +588,15 @@ static void sock_map_free(struct bpf_map *map) =20 write_lock_bh(&sock->sk_callback_lock); psock =3D smap_psock_sk(sock); - smap_list_remove(psock, &stab->sock_map[i]); - smap_release_sock(psock, sock); + /* This check handles a racing sock event that can get the + * sk_callback_lock before this case but after xchg happens + * causing the refcnt to hit zero and sock user data (psock) + * to be null and queued for garbage collection. + */ + if (likely(psock)) { + smap_list_remove(psock, &stab->sock_map[i]); + smap_release_sock(psock, sock); + } write_unlock_bh(&sock->sk_callback_lock); } rcu_read_unlock(); --=20 2.11.0