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rtld: Check __libc_enable_secure before honoring LD_PREFER_MAP_32BIT_EXEC (CVE-2019-19126) [BZ #25204]

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The problem was introduced in glibc 2.23, in commit
b9eb92ab05
("Add Prefer_MAP_32BIT_EXEC to map executable pages with MAP_32BIT").
This commit is contained in:
Marcin Kościelnicki
2019-11-21 00:20:15 +01:00
committed by Florian Weimer
parent 2a764c6ee8
commit d5dfad4326
2 changed files with 7 additions and 2 deletions
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6
NEWS
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@ -86,7 +86,11 @@ Changes to build and runtime requirements:
Security related changes: 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: The following bugs are resolved with this release:

3
sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
View File

@ -31,7 +31,8 @@
environment variable, LD_PREFER_MAP_32BIT_EXEC. */ environment variable, LD_PREFER_MAP_32BIT_EXEC. */
#define EXTRA_LD_ENVVARS \ #define EXTRA_LD_ENVVARS \
case 21: \ 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] \ GLRO(dl_x86_cpu_features).feature[index_arch_Prefer_MAP_32BIT_EXEC] \
|= bit_arch_Prefer_MAP_32BIT_EXEC; \ |= bit_arch_Prefer_MAP_32BIT_EXEC; \
break; break;