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[PATCH] rtld: Check __libc_enable_secure before honoring LD_PREFER_MAP_32BIT_EXEC (CVE-2019-19126) [BZ #25204]
- From: Marcin Kościelnicki <mwk at 0x04 dot net>
- To: libc-alpha at sourceware dot org
- Cc: Marcin Kościelnicki <mwk at 0x04 dot net>
- Date: Thu, 21 Nov 2019 00:20:15 +0100
- Subject: [PATCH] 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").
---
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;
--
2.23.0