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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>
This commit is contained in:
Ingo Molnar 2008-02-06 22:39:44 +01:00
parent 4cc6028d40
commit 32a932332c
3 changed files with 25 additions and 2 deletions
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2
fs/binfmt_elf.c
View File

@ -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

12
init/Kconfig
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@ -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

13
mm/memory.c
View File

@ -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)
{