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Biederman" CC: Christian Brauner , Kees Cook , Jann Horn , Jonathan Corbet , Alexander Viro , Andrew Morton , Alexey Dobriyan , Thomas Gleixner , Oleg Nesterov , Frederic Weisbecker , Andrei Vagin , Ingo Molnar , "Peter Zijlstra (Intel)" , Yuyang Du , David Hildenbrand , Sebastian Andrzej Siewior , Anshuman Khandual , David Howells , James Morris , Greg Kroah-Hartman , Shakeel Butt , Jason Gunthorpe , Christian Kellner , Andrea Arcangeli , Aleksa Sarai , "Dmitry V. Levin" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "stable@vger.kernel.org" , "linux-api@vger.kernel.org" Subject: Re: [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex Thread-Topic: [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex Thread-Index: AQHV9ZJHYfsGvDLnM0SksOJ5MpqOZahARvEAgABCQ42AAAUtgIAAA0/bgAADytmAAANO2YAAAnOA Date: Mon, 9 Mar 2020 18:47:33 +0000 Message-ID: References: <87v9nlii0b.fsf@x220.int.ebiederm.org> <87a74xi4kz.fsf@x220.int.ebiederm.org> <87r1y8dqqz.fsf@x220.int.ebiederm.org> <87tv32cxmf.fsf_-_@x220.int.ebiederm.org> <87v9ne5y4y.fsf_-_@x220.int.ebiederm.org> <87zhcq4jdj.fsf_-_@x220.int.ebiederm.org> <878sk94eay.fsf@x220.int.ebiederm.org> <87r1y12yc7.fsf@x220.int.ebiederm.org> <87k13t2xpd.fsf@x220.int.ebiederm.org> <87d09l2x5n.fsf@x220.int.ebiederm.org> In-Reply-To: <87d09l2x5n.fsf@x220.int.ebiederm.org> Accept-Language: en-US, en-GB, de-DE Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-clientproxiedby: AM4PR0101CA0058.eurprd01.prod.exchangelabs.com (2603:10a6:200:41::26) To AM6PR03MB5170.eurprd03.prod.outlook.com (2603:10a6:20b:ca::23) x-incomingtopheadermarker: OriginalChecksum:17D50A9079693C9730F13F4FCFB4C58965ABDABB018076CCCBFAE6141CCBDE09;UpperCasedChecksum:943194F64A5F2251D16D357F1D689DF5F732291536CA9783E0600AACAC54A29E;SizeAsReceived:9977;Count:50 x-ms-exchange-messagesentrepresentingtype: 1 x-tmn: [3oQ7Uxmx+ynr7v1Spcc0igVUIJqKghv9] x-microsoft-original-message-id: x-ms-publictraffictype: Email x-incomingheadercount: 50 x-eopattributedmessage: 0 x-ms-office365-filtering-correlation-id: bef8d83c-f9a0-4369-50ba-08d7c45a542a x-ms-traffictypediagnostic: DB5EUR03HT121: x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: mcxWwbqx6jZv4TamNQqlbiI3Ar93DM75YP5msmSrCZjI/hoFC3oQ46BxTJl3n+VOJJSe4sSheD6A3eCiWVtE0ftx/0/JGvbMuoXDpyaVdCNTRlCmY8yNKgZaXfrrWWmJFpLJNSkoaQcut6w3vPEEBahop63tE4IUHri6twFVuZ8RkaAf7t5zpKVDPnVR75Gr1yrzyomjNFF3JiNaqREUgpwEa4ByxM0nfyzSqo6Q1kU= x-ms-exchange-antispam-messagedata: Ax8gQJ7eltKZ1TbGEo1FsMhWsQ+vm8pGzfoym/VXJYqaA9QznsnNPidOSbTJKFGRocdUqPFFZxmPN/ubXrMBauR919P0Omwp9LEP6ExRpiXSa7mgOlIutNoKz8V+oQ6j80entIMyByasDOgukM/6Xw== x-ms-exchange-transport-forked: True Content-Type: text/plain; charset="Windows-1252" Content-ID: <3A42B7F095068546B228DA429521FE49@eurprd03.prod.outlook.com> Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-OriginatorOrg: outlook.com X-MS-Exchange-CrossTenant-RMS-PersistedConsumerOrg: 00000000-0000-0000-0000-000000000000 X-MS-Exchange-CrossTenant-Network-Message-Id: bef8d83c-f9a0-4369-50ba-08d7c45a542a X-MS-Exchange-CrossTenant-rms-persistedconsumerorg: 00000000-0000-0000-0000-000000000000 X-MS-Exchange-CrossTenant-originalarrivaltime: 09 Mar 2020 18:47:33.7822 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Internet X-MS-Exchange-CrossTenant-id: 84df9e7f-e9f6-40af-b435-aaaaaaaaaaaa X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB5EUR03HT121 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/9/20 7:36 PM, Eric W. Biederman wrote: > > My rewritten change description reads as follows: > > exec: Add a exec_update_mutex to replace cred_guard_mutex is this "an" exec_update_mutex? > > The cred_guard_mutex is problematic as it is held over possibly > indefinite waits for userspace. The possilbe indefinite waits for > userspace that I have identified are: The cred_guard_mutex is held in > PTRACE_EVENT_EXIT waiting for the tracer. The cred_guard_mutex is > held over "put_user(0, tsk->clear_child_tid)" in exit_mm(). The > cred_guard_mutex is held over "get_user(futex_offset, ...") in > exit_robust_list. The cred_guard_mutex held over copy_strings. > > The functions get_user and put_user can trigger a page fault which can > potentially wait indefinitely in the case of userfaultfd or if > userspace implements part of the page fault path. > > In any of those cases the userspace process that the kernel is waiting > for might userspace might make a different system call that winds up ^-------------^ ^- remove this > taking the cred_guard_mutex and result in deadlock. > > Holding a mutex over any of those possibly indefinite waits for > userspace does not appear necessary. Add exec_update_mutex that will > just cover updating the process during exec where the permissions and > the objects pointed to by the task struct may be out of sync. > > The plan is to switch the users of cred_guard_mutex to > exec_udpate_mutex one by one. This lets us move forward while still ^-- typo: update > being careful and not introducing any regressions. > > Link: https://lore.kernel.org/lkml/20160921152946.GA24210@dhcp22.suse.cz/ > Link: https://lore.kernel.org/lkml/AM6PR03MB5170B06F3A2B75EFB98D071AE4E60@AM6PR03MB5170.eurprd03.prod.outlook.com/ > Link: https://lore.kernel.org/linux-fsdevel/20161102181806.GB1112@redhat.com/ > Link: https://lore.kernel.org/lkml/20160923095031.GA14923@redhat.com/ > Link: https://lore.kernel.org/lkml/20170213141452.GA30203@redhat.com/ > Ref: 45c1a159b85b ("Add PTRACE_O_TRACEVFORKDONE and PTRACE_O_TRACEEXIT facilities.") > Ref: 456f17cd1a28 ("[PATCH] user-vm-unlock-2.5.31-A2") > Signed-off-by: "Eric W. Biederman" > > Does that sound better? > almost done. > Eric >