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 16253 invoked from network); 10 Aug 2020 15:41:37 -0000 Received: from mother.openwall.net (195.42.179.200) by inbox.vuxu.org with ESMTPUTF8; 10 Aug 2020 15:41:37 -0000 Received: (qmail 32163 invoked by uid 550); 10 Aug 2020 15:41:35 -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 32139 invoked from network); 10 Aug 2020 15:41:35 -0000 Date: Mon, 10 Aug 2020 17:41:23 +0200 From: Szabolcs Nagy To: Olaf Flebbe Cc: musl@lists.openwall.com Message-ID: <20200810154123.GC879655@port70.net> Mail-Followup-To: Olaf Flebbe , musl@lists.openwall.com References: <20200809003958.GE3265@brightrain.aerifal.cx> <2142D551-13BE-4033-94F7-80A7B2C01890@oflebbe.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2142D551-13BE-4033-94F7-80A7B2C01890@oflebbe.de> Subject: Re: [musl] Revisiting sigaltstack and implementation-internal signals * 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.