From patchwork Wed Nov 20 23:20:15 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Marcin_Ko=C5=9Bcielnicki?= X-Patchwork-Id: 36077 Received: (qmail 124307 invoked by alias); 20 Nov 2019 23:20:33 -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 124291 invoked by uid 89); 20 Nov 2019 23:20:33 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-19.4 required=5.0 tests=AWL, BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, SPF_PASS autolearn=ham version=3.3.1 spammy=HContent-Transfer-Encoding:8bit X-HELO: xyzzy.0x04.net From: =?UTF-8?q?Marcin=20Ko=C5=9Bcielnicki?= To: libc-alpha@sourceware.org Cc: =?UTF-8?q?Marcin=20Ko=C5=9Bcielnicki?= Subject: [PATCH] rtld: Check __libc_enable_secure before honoring LD_PREFER_MAP_32BIT_EXEC (CVE-2019-19126) [BZ #25204] Date: Thu, 21 Nov 2019 00:20:15 +0100 Message-Id: <20191120232015.25936-1-mwk@0x04.net> MIME-Version: 1.0 The problem was introduced in glibc 2.23, in commit b9eb92ab05204df772eb4929eccd018637c9f3e9 ("Add Prefer_MAP_32BIT_EXEC to map executable pages with MAP_32BIT"). --- NEWS | 6 +++++- sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h | 3 ++- 2 files changed, 7 insertions(+), 2 deletions(-) diff --git a/NEWS b/NEWS index 50479f17c9..df03f4dc48 100644 --- a/NEWS +++ b/NEWS @@ -86,7 +86,11 @@ Changes to build and runtime requirements: Security related changes: - [Add security related changes here] + CVE-2019-19126: ld.so failed to ignore the LD_PREFER_MAP_32BIT_EXEC + environment variable during program execution after a security + transition, allowing local attackers to restrict the possible mapping + addresses for loaded libraries and thus bypass ASLR for a setuid + program. Reported by Marcin Kościelnicki. The following bugs are resolved with this release: diff --git a/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h b/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h index 0e95221908..e3af239faa 100644 --- a/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h +++ b/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h @@ -31,7 +31,8 @@ environment variable, LD_PREFER_MAP_32BIT_EXEC. */ #define EXTRA_LD_ENVVARS \ case 21: \ - if (memcmp (envline, "PREFER_MAP_32BIT_EXEC", 21) == 0) \ + if (!__libc_enable_secure \ + && memcmp (envline, "PREFER_MAP_32BIT_EXEC", 21) == 0) \ GLRO(dl_x86_cpu_features).feature[index_arch_Prefer_MAP_32BIT_EXEC] \ |= bit_arch_Prefer_MAP_32BIT_EXEC; \ break;