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authorIngo Molnar <mingo@elte.hu>2008-02-06 22:39:44 +0100
committerIngo Molnar <mingo@elte.hu>2008-02-06 22:39:44 +0100
commit32a932332c8bad842804842eaf9651ad6268e637 (patch)
tree58f187409029f089f788c5c35ad5c200b4a555af
parent4cc6028d4040f95cdb590a87db478b42b8be0508 (diff)
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>
-rw-r--r--fs/binfmt_elf.c2
-rw-r--r--init/Kconfig12
-rw-r--r--mm/memory.c13
3 files changed, 25 insertions, 2 deletions
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 4628c42ca89..111771d38e6 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -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
diff --git a/init/Kconfig b/init/Kconfig
index 87f50df5889..92b23e25661 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -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
diff --git a/mm/memory.c b/mm/memory.c
index 7bb70728bb5..9d073fa0a2d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -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)
{