brk randomization: introduce CONFIG_COMPAT_BRK
based on similar patch from: Pavel Machek <pavel@ucw.cz>
Introduce CONFIG_COMPAT_BRK. If disabled then the kernel is free
(but not obliged to) randomize the brk area.
Heap randomization breaks ancient binaries, so we keep COMPAT_BRK
enabled by default.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 4628c42..111771d 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1077,7 +1077,7 @@
current->mm->start_stack = bprm->p;
#ifdef arch_randomize_brk
- if (current->flags & PF_RANDOMIZE)
+ if ((current->flags & PF_RANDOMIZE) && (randomize_va_space > 1))
current->mm->brk = current->mm->start_brk =
arch_randomize_brk(current->mm);
#endif
diff --git a/init/Kconfig b/init/Kconfig
index 87f50df..92b23e2 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -541,6 +541,18 @@
help
Enable support for generating core dumps. Disabling saves about 4k.
+config COMPAT_BRK
+ bool "Disable heap randomization"
+ default y
+ help
+ Randomizing heap placement makes heap exploits harder, but it
+ also breaks ancient binaries (including anything libc5 based).
+ This option changes the bootup default to heap randomization
+ disabled, and can be overriden runtime by setting
+ /proc/sys/kernel/randomize_va_space to 2.
+
+ On non-ancient distros (post-2000 ones) Y is usually a safe choice.
+
config BASE_FULL
default y
bool "Enable full-sized data structures for core" if EMBEDDED
diff --git a/mm/memory.c b/mm/memory.c
index 7bb7072..9d073fa 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -82,7 +82,18 @@
EXPORT_SYMBOL(num_physpages);
EXPORT_SYMBOL(high_memory);
-int randomize_va_space __read_mostly = 1;
+/*
+ * Randomize the address space (stacks, mmaps, brk, etc.).
+ *
+ * ( When CONFIG_COMPAT_BRK=y we exclude brk from randomization,
+ * as ancient (libc5 based) binaries can segfault. )
+ */
+int randomize_va_space __read_mostly =
+#ifdef CONFIG_COMPAT_BRK
+ 1;
+#else
+ 2;
+#endif
static int __init disable_randmaps(char *s)
{