* [2.26 COMMITTED] rtld: Check __libc_enable_secure before honoring LD_PREFER_MAP_32BIT_EXEC (CVE-2019-19126) [BZ #25204]
@ 2019-01-01 0:00 Florian Weimer
0 siblings, 0 replies; only message in thread
From: Florian Weimer @ 2019-01-01 0:00 UTC (permalink / raw)
To: libc-stable
From: Marcin Kościelnicki <mwk@0x04.net>
The problem was introduced in glibc 2.23, in commit
b9eb92ab05204df772eb4929eccd018637c9f3e9
("Add Prefer_MAP_32BIT_EXEC to map executable pages with MAP_32BIT").
(cherry picked from commit d5dfad4326fc683c813df1e37bbf5cf920591c8e)
diff --git a/NEWS b/NEWS
index c6c44a3914..89adc868bb 100644
--- a/NEWS
+++ b/NEWS
@@ -100,6 +100,12 @@ Security related changes:
memcmp gave the wrong result since it treated the size argument as
zero. Reported by H.J. Lu.
+ 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:
[16750] ldd: Never run file directly.
@@ -182,6 +188,7 @@ The following bugs are resolved with this release:
[24027] malloc: Integer overflow in realloc
[24097] Can't use 64-bit register for size_t in assembly codes for x32 (CVE-2019-6488)
[24155] x32 memcmp can treat positive length as 0 (if sign bit in RDX is set) (CVE-2019-7309)
+ [25204] Ignore LD_PREFER_MAP_32BIT_EXEC for SUID programs
\f
Version 2.26
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 8d474d0d04..37f0b14adb 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;
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2019-01-01 0:00 [2.26 COMMITTED] rtld: Check __libc_enable_secure before honoring LD_PREFER_MAP_32BIT_EXEC (CVE-2019-19126) [BZ #25204] Florian Weimer
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