From patchwork Wed Aug 28 09:06:05 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Liebler X-Patchwork-Id: 34293 Received: (qmail 65088 invoked by alias); 28 Aug 2019 09:06:17 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 65073 invoked by uid 89); 28 Aug 2019 09:06:16 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-22.6 required=5.0 tests=AWL, BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, KAM_SHORT, RCVD_IN_DNSWL_LOW, SPF_PASS autolearn=ham version=3.3.1 spammy=H*f:sk:3b9cb5e, H*i:sk:3b9cb5e X-HELO: mx0a-001b2d01.pphosted.com Subject: Re: [PATCH] Add UNSUPPORTED check in elf/tst-pldd. To: libc-alpha@sourceware.org References: <877e6yiqsn.fsf@oldenburg2.str.redhat.com> <3b9cb5e4-7c9a-c9a4-449e-43ba98a6ad01@linaro.org> From: Stefan Liebler Date: Wed, 28 Aug 2019 11:06:05 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <3b9cb5e4-7c9a-c9a4-449e-43ba98a6ad01@linaro.org> x-cbid: 19082809-4275-0000-0000-0000035E3D7A X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19082809-4276-0000-0000-0000387070CE Message-Id: <32961942-e67b-c356-a92d-b6e45c8aaf9d@linux.ibm.com> On 8/27/19 9:11 PM, Adhemerval Zanella wrote: > > > On 27/08/2019 12:14, Florian Weimer wrote: >> * Adhemerval Zanella: >> >>> This is a Linuxism and I think we should create a 'support_can_ptrace' >>> similar to 'support_can_chroot'. The logic to detect it seems >>> correct, I would just check fscanf returned to value and use xfclose. >>> It would be something like >> >> The test does the right thing if the path does not exist, so I'm not >> sure if it is necessary. > > Even though, a check for a Linux specific path should be restricted to > Linux builds only. > >> >> support_can_ptrace would be misleading because even with YAMA scope >> support, tracing direct subprocesses will still work. > > Indeed, a better prototype would be indeed: > > /* Return the current YAMA mode set on the machine (0 to 3) or -1 > if YAMA is not supported. */ > int support_ptrace_scope (void); > >> >> I fact, I think we might be able to get this test to work even with >> fairly restrictive YAMA scopes, by proper ordering of forks and using >> execve to run tst-pldd. > > The problem with ptrace_scope 1 is tst-pldd will either make its fork > helper process a pldd descendant or pass pldd pid to the forked process > so it can call prctl (PR_SET_PTRACER, ...). In either case I am not > really sure it is possible without change pldd process itself (since > it does not have an interactive mode), nor if the complexity to support > this specific scenarios pays off. > > The ptrace_scope 2 is even more tricky since it requires CAP_SYS_PTRACE. > > In any case I think by restricting the test to run on ptrace_scope 0 > is a fair assumption. > >> >> Thanks, >> Florian >> Please have a look at the adjusted the patch. I've introduced new support functions. And if ptrace_scope is 1 "restricted ptrace", I've just call prctl (PR_SET_PTRACER, PR_SET_PTRACER_ANY,...) on the target process. This way the target process does not need to know the pid of pldd and pldd is allowed to attach to the target process. If ptrace_scope is 2 or 3, the test is marked as UNSUPPORTED. Thanks. Stefan commit 7eba88e4f44df6f4a6d174e566b1796f2abc490c Author: Stefan Liebler Date: Mon Aug 26 15:45:07 2019 +0200 Add UNSUPPORTED check in elf/tst-pldd. The testcase forks a child process and runs pldd with PID of this child. On systems where /proc/sys/kernel/yama/ptrace_scope differs from zero, pldd will fail with /usr/bin/pldd: cannot attach to process 3: Operation not permitted This patch checks if ptrace_scope exists, is zero "classic ptrace permissions" or one "restricted ptrace". In case of "restricted ptrace", we can effectively disable the restriction by using prctl (PR_SET_PTRACER_ANY). If ptrace_scope exists and has a higher restriction, then the test is marked as UNSUPPORTED. ChangeLog: * elf/tst-pldd.c (do_test): Add UNSUPPORTED check. (target_process): Disable restricted ptrace. * support/Makefile (libsupport-routines): Add support_ptrace. * support/ptrace.h: New file. * support/support_ptrace.c: Likewise. diff --git a/elf/tst-pldd.c b/elf/tst-pldd.c index 6b7c94a1c0..728272d177 100644 --- a/elf/tst-pldd.c +++ b/elf/tst-pldd.c @@ -30,10 +30,20 @@ #include #include #include +#include + +static int ptrace_scope; static void target_process (void *arg) { + if (ptrace_scope == 1) + { + /* YAMA is configured to "restricted ptrace". + Disable the restriction for this subprocess. */ + support_ptrace_process_set_ptracer_any (); + } + pause (); } @@ -52,6 +62,11 @@ in_str_list (const char *libname, const char *const strlist[]) static int do_test (void) { + /* Check if our subprocess can be debugged with ptrace. */ + ptrace_scope = support_ptrace_scope (); + if (ptrace_scope >= 2) + FAIL_UNSUPPORTED ("/proc/sys/kernel/yama/ptrace_scope >= 2"); + /* Create a copy of current test to check with pldd. */ struct support_subprocess target = support_subprocess (target_process, NULL); diff --git a/support/Makefile b/support/Makefile index ab66913a02..34d14eb1bb 100644 --- a/support/Makefile +++ b/support/Makefile @@ -56,6 +56,7 @@ libsupport-routines = \ support_format_hostent \ support_format_netent \ support_isolate_in_subprocess \ + support_ptrace \ support_openpty \ support_paths \ support_quote_blob \ diff --git a/support/ptrace.h b/support/ptrace.h new file mode 100644 index 0000000000..82f79ff25c --- /dev/null +++ b/support/ptrace.h @@ -0,0 +1,36 @@ +/* Support functions handling ptrace_scope. + Copyright (C) 2019 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#ifndef SUPPORT_PTRACE_H +#define SUPPORT_PTRACE_H + +#include + +__BEGIN_DECLS + +/* Return the current YAMA mode set on the machine (0 to 3) or -1 + if YAMA is not supported. */ +int support_ptrace_scope (void); + +/* Effectively disables YAMA restriction for the calling process + if support_ptrace_scope returns 1 "restricted ptrace". */ +void support_ptrace_process_set_ptracer_any (void); + +__END_DECLS + +#endif diff --git a/support/support_ptrace.c b/support/support_ptrace.c new file mode 100644 index 0000000000..e9410384b5 --- /dev/null +++ b/support/support_ptrace.c @@ -0,0 +1,58 @@ +/* Support functions handling ptrace_scope. + Copyright (C) 2019 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#include +#include +#include +#include + +int +support_ptrace_scope (void) +{ + int ptrace_scope = -1; + +#ifdef __linux__ + /* YAMA may be not enabled. Otherwise it contains a value from 0 to 3: + - 0 classic ptrace permissions + - 1 restricted ptrace + - 2 admin-only attach + - 3 no attach */ + FILE *f = fopen ("/proc/sys/kernel/yama/ptrace_scope", "r"); + if (f != NULL) + { + TEST_COMPARE (fscanf (f, "%d", &ptrace_scope), 1); + xfclose (f); + } +#endif + + return ptrace_scope; +} + +void +support_ptrace_process_set_ptracer_any (void) +{ +#ifdef __linux__ + int ret = prctl (PR_SET_PTRACER, PR_SET_PTRACER_ANY, 0, 0, 0); + if (ret != 0) + FAIL_EXIT1 ("Failed to disable YAMA restriction. (prctl returned %d: %m)", + ret); +#else + FAIL_UNSUPPORTED ("prctl (PR_SET_PTRACER, PR_SET_PTRACER_ANY, ...) " + "not supported!"); +#endif +}