brk randomization: introduce CONFIG_COMPAT_BRK

based on similar patch from: Pavel Machek <[email protected]> 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 <[email protected]>
chewitt · Feb 6, 2008 · 32a9323 · 32a9323
1 parent 4cc6028
commit 32a9323
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Showing 3 changed files with 25 additions and 2 deletions.
diff --git 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
@@ -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
@@ -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)
 {