From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-3.3 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 20871 invoked from network); 10 Aug 2020 16:24:56 -0000 Received: from mother.openwall.net (195.42.179.200) by inbox.vuxu.org with ESMTPUTF8; 10 Aug 2020 16:24:56 -0000 Received: (qmail 20167 invoked by uid 550); 10 Aug 2020 16:24:53 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 20149 invoked from network); 10 Aug 2020 16:24:53 -0000 Date: Mon, 10 Aug 2020 18:24:41 +0200 From: Szabolcs Nagy To: Olaf Flebbe Cc: musl@lists.openwall.com Message-ID: <20200810162441.GD879655@port70.net> Mail-Followup-To: Olaf Flebbe , musl@lists.openwall.com References: <20200809003958.GE3265@brightrain.aerifal.cx> <2142D551-13BE-4033-94F7-80A7B2C01890@oflebbe.de> <20200810154123.GC879655@port70.net> <4B4992FA-A648-46FB-9DD7-48D045867EA4@oflebbe.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4B4992FA-A648-46FB-9DD7-48D045867EA4@oflebbe.de> Subject: Re: [musl] Revisiting sigaltstack and implementation-internal signals * Olaf Flebbe [2020-08-10 17:45:06 +0200]: > > Am 10.08.2020 um 17:41 schrieb Szabolcs Nagy : > > * Olaf Flebbe [2020-08-10 10:15:13 +0200]: > >> I have some problems to follow the discussion here. > >> > >> It is not about musl to create an alternate stack, it is to *honor* the alternate stack, if the application installed one, for a reason. > >> > >> I am proposing smthg like > >> > >> --- /oss/musl-1.2.1/src/thread/synccall.c > >> +++ /work/musl/src/thread/synccall.c > >> @@ -45,7 +45,7 @@ > >> { > >> sigset_t oldmask; > >> int cs, i, r; > >> - struct sigaction sa = { .sa_flags = SA_RESTART, .sa_handler = handler }; > >> + struct sigaction sa = { .sa_flags = SA_RESTART|SA_ONSTACK, .sa_handler = handler }; > >> pthread_t self = __pthread_self(), td; > >> int count = 0; > >> > >> This will fix the problem with dynamic stacks, like go implements it. > >> If the application does not install one, kernel will ignore SA_ONSTACK. (This is even specified by POSIX, since there is no error condition mentioned in man page specifically for this). > >> > >> Tested with go and a glibc threaded setuid test tst-setuid3.c . > > > > this will fail if an application calls sigaltstack, > > then blocks all user signals that are SA_ONSTACK and > > then deallocates the stack passed to sigaltstack. > > > > it is important to discuss what an application may > > or may not do, because the proposed change observably > > modifies the behaviour. > > > Deallocating an assigned sigaltstack without resetting sigaltstack is undefined behaviour. i don't see where posix specifies the lifetime of the stack registered with sigaltstack.