From patchwork Tue Oct 13 13:58:56 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Florian Weimer X-Patchwork-Id: 9081 Received: (qmail 103208 invoked by alias); 13 Oct 2015 13:59:03 -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 103197 invoked by uid 89); 13 Oct 2015 13:59:02 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.6 required=5.0 tests=AWL, BAYES_00, SPF_HELO_PASS, T_RP_MATCHES_RCVD autolearn=ham version=3.3.2 X-HELO: mx1.redhat.com Subject: Re: [PATCH] Ignore LD_POINTER_GUARD for set-user-ID/set-group-ID binaries. To: GNU C Library References: <1441471191-4683-1-git-send-email-hecmargi@upv.es> <56162CD0.4070902@redhat.com> <5618710F.6060406@redhat.com> <20151011001054.GC4119@vapier.lan> From: Florian Weimer X-Enigmail-Draft-Status: N1010 Cc: "Carlos O'Donell" , Hector Marco-Gisbert , "Joseph S. Myers" , Siddhesh Poyarekar , Andreas Jaeger , Ismael Ripoll Ripoll Message-ID: <561D0E20.3000409@redhat.com> Date: Tue, 13 Oct 2015 15:58:56 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <20151011001054.GC4119@vapier.lan> On 10/11/2015 02:10 AM, Mike Frysinger wrote: > On 09 Oct 2015 21:59, Carlos O'Donell wrote: >> On 10/08/2015 04:44 AM, Florian Weimer wrote: >>> On 09/05/2015 06:39 PM, Hector Marco-Gisbert wrote: >>>> A weakness in the dynamic loader have been found, Glibc prior to >>>> 2.22.90 are affected. The issue is that the LD_POINTER_GUARD in the >>>> environment is not sanitized allowing local attackers easily to bypass >>>> the pointer guarding protection on set-user-ID and set-group-ID >>>> programs. >>>> >>>> Details of the weakness: >>>> http://hmarco.org/bugs/glibc_ptr_mangle_weakness.html >>>> >>>> This patch prevents to disable the pointer guarding protection for >>>> set-user-ID/set-group-ID programs. >>>> >>>> For example, executing "LD_POINTER_GUARD=0 /bin/ping" does not disable >>>> the pointer guarding protection unless it is directly executed by root >>>> (rUID==eUID). >>> >>> Does anyone actually use LD_POINTER_GUARD for debugging? Maybe we can >>> simply retire the environment variable instead. >> >> I vote we remove it. It has long since passed the point of usefullness. >> With a proper tunables infrastructure we would have added it in one release >> while we tested things, and then removed it one or two releases later. > > sounds fine to me. punt it and be done. Great, then let's do it. (I have an idea how we can preserve backwards compatibility even if we have some form of libio vtable hardening, so we don't have to keep around LD_POINTER_GUARD for the sake of old applications.) Florian Always enable pointer guard [BZ #18928] Honoring the LD_POINTER_GUARD environment variable in AT_SECURE mode has security implications. This commit enables pointer guard unconditionally, and the environment variable is now ignored. 2015-10-13 Florian Weimer [BZ #18928] * sysdeps/generic/ldsodefs.h (struct rtld_global_ro): Remove _dl_pointer_guard member. * elf/rtld.c (_rtld_global_ro): Remove _dl_pointer_guard initializer. (security_init): Always set up pointer guard. (process_envvars): Do not process LD_POINTER_GUARD. diff --git a/NEWS b/NEWS index 478ed2d..0d1cc3b 100644 --- a/NEWS +++ b/NEWS @@ -16,10 +16,13 @@ Version 2.23 18265, 18370, 18421, 18480, 18525, 18595, 18589, 18610, 18618, 18647, 18661, 18674, 18675, 18681, 18724, 18757, 18778, 18781, 18787, 18789, 18790, 18795, 18796, 18803, 18820, 18823, 18824, 18825, 18857, 18863, - 18870, 18872, 18873, 18875, 18887, 18921, 18951, 18952, 18956, 18961, - 18966, 18967, 18969, 18970, 18977, 18980, 18981, 18985, 19003, 19012, - 19016, 19018, 19032, 19046, 19049, 19050, 19059, 19071, 19076, 19077, - 19078, 19079, 19085, 19086, 19088, 19094, 19095. + 18870, 18872, 18873, 18875, 18887, 18921, 18928, 18951, 18952, 18956, + 18961, 18966, 18967, 18969, 18970, 18977, 18980, 18981, 18985, 19003, + 19012, 19016, 19018, 19032, 19046, 19049, 19050, 19059, 19071, 19076, + 19077, 19078, 19079, 19085, 19086, 19088, 19094, 19095. + +* The LD_POINTER_GUARD environment variable can no longer be used to disable + the pointer guard feature. It is always enabled. * The obsolete header has been removed. Programs that require this header must be updated to use instead. diff --git a/elf/rtld.c b/elf/rtld.c index 1474c72..52160df 100644 --- a/elf/rtld.c +++ b/elf/rtld.c @@ -162,7 +162,6 @@ struct rtld_global_ro _rtld_global_ro attribute_relro = ._dl_hwcap_mask = HWCAP_IMPORTANT, ._dl_lazy = 1, ._dl_fpu_control = _FPU_DEFAULT, - ._dl_pointer_guard = 1, ._dl_pagesize = EXEC_PAGESIZE, ._dl_inhibit_cache = 0, @@ -709,15 +708,12 @@ security_init (void) #endif /* Set up the pointer guard as well, if necessary. */ - if (GLRO(dl_pointer_guard)) - { - uintptr_t pointer_chk_guard = _dl_setup_pointer_guard (_dl_random, - stack_chk_guard); + uintptr_t pointer_chk_guard + = _dl_setup_pointer_guard (_dl_random, stack_chk_guard); #ifdef THREAD_SET_POINTER_GUARD - THREAD_SET_POINTER_GUARD (pointer_chk_guard); + THREAD_SET_POINTER_GUARD (pointer_chk_guard); #endif - __pointer_chk_guard_local = pointer_chk_guard; - } + __pointer_chk_guard_local = pointer_chk_guard; /* We do not need the _dl_random value anymore. The less information we leave behind, the better, so clear the @@ -2471,9 +2467,6 @@ process_envvars (enum mode *modep) GLRO(dl_use_load_bias) = envline[14] == '1' ? -1 : 0; break; } - - if (memcmp (envline, "POINTER_GUARD", 13) == 0) - GLRO(dl_pointer_guard) = envline[14] != '0'; break; case 14: diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h index 7f7ff72..0625826 100644 --- a/sysdeps/generic/ldsodefs.h +++ b/sysdeps/generic/ldsodefs.h @@ -592,9 +592,6 @@ struct rtld_global_ro /* List of auditing interfaces. */ struct audit_ifaces *_dl_audit; unsigned int _dl_naudit; - - /* 0 if internal pointer values should not be guarded, 1 if they should. */ - EXTERN int _dl_pointer_guard; }; # define __rtld_global_attribute__ # if IS_IN (rtld)