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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").

(cherry picked from commit d5dfad4326)
This commit is contained in:
Marcin Kościelnicki 2019-11-21 00:20:15 +01:00 committed by Florian Weimer
parent cedb3e47c6
commit 7966ce07e8
2 changed files with 10 additions and 1 deletions
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8
NEWS
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@ -69,6 +69,7 @@ The following bugs are resolved with this release:
[24228] old x86 applications that use legacy libio crash on exit
[24476] dlfcn: Guard __dlerror_main_freeres with __libc_once_get (once)
[24744] io: Remove the copy_file_range emulation.
[25204] Ignore LD_PREFER_MAP_32BIT_EXEC for SUID programs
Security related changes:
@ -97,6 +98,13 @@ Security related changes:
CVE-2019-9169: Attempted case-insensitive regular-expression match
via proceed_next_node in posix/regexec.c leads to heap-based buffer
over-read. Reported by Hongxu Chen.
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.
Version 2.28

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

@ -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;