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Commit 32a93233 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

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: default avatarIngo Molnar <mingo@elte.hu>
parent 4cc6028d

fs/binfmt_elf.c

+1 −1
Original line number Diff line number Diff line
@@ -1077,7 +1077,7 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs) 
	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

init/Kconfig

+12 −0
Original line number Diff line number Diff line
@@ -541,6 +541,18 @@ config ELF_CORE 
	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

mm/memory.c

+12 −1
Original line number Diff line number Diff line
@@ -82,7 +82,18 @@ void * high_memory; 
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)

{