https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=d5dfad4326fc683c813df1e37bbf5cf920591c8e commit d5dfad4326fc683c813df1e37bbf5cf920591c8e Author: Marcin Kościelnicki Date: Thu Nov 21 00:20:15 2019 +0100 rtld: Check __libc_enable_secure before honoring LD_PREFER_MAP_32BIT_EXEC (CVE-2019-19126) [BZ #25204] The problem was introduced in glibc 2.23, in commit b9eb92ab05204df772eb4929eccd018637c9f3e9 ("Add Prefer_MAP_32BIT_EXEC to map executable pages with MAP_32BIT"). Diff: --- 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 50479f1..df03f4d 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 0e95221..e3af239 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;