Commit 4471a675 authored Apr 14, 2011 by Jiri Kosina Committed by Linus Torvalds Apr 14, 2011

brk: COMPAT_BRK: fix detection of randomized brk



5520e894 ("brk: fix min_brk lower bound computation for COMPAT_BRK")
tried to get the whole logic of brk randomization for legacy
(libc5-based) applications finally right.

It turns out that the way to detect whether brk has actually been
randomized in the end or not introduced by that patch still doesn't work
for those binaries, as reported by Geert:

: /sbin/init from my old m68k ramdisk exists prematurely.
:
: Before the patch:
:
: | brk(0x80005c8e)                         = 0x80006000
:
: After the patch:
:
: | brk(0x80005c8e)                         = 0x80005c8e
:
: Old libc5 considers brk() to have failed if the return value is not
: identical to the requested value.

I don't like it, but currently see no better option than a bit flag in
task_struct to catch the CONFIG_COMPAT_BRK && randomize_va_space == 2
case.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 5de1743e

fs/binfmt_elf.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -941,9 +941,13 @@ 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) && (randomize_va_space > 1))
		if ((current->flags & PF_RANDOMIZE) && (randomize_va_space > 1)) {
		current->mm->brk = current->mm->start_brk =
		arch_randomize_brk(current->mm);
		#ifdef CONFIG_COMPAT_BRK
		current->brk_randomized = 1;
		#endif
		}
		#endif

		if (current->personality & MMAP_PAGE_ZERO) {

include/linux/sched.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -1254,6 +1254,9 @@ struct task_struct {
		#endif

		struct mm_struct mm, active_mm;
		#ifdef CONFIG_COMPAT_BRK
		unsigned brk_randomized:1;
		#endif
		#if defined(SPLIT_RSS_COUNTING)
		struct task_rss_stat rss_stat;
		#endif

mm/mmap.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -259,7 +259,7 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
		* randomize_va_space to 2, which will still cause mm->start_brk
		* to be arbitrarily shifted
		*/
		if (mm->start_brk > PAGE_ALIGN(mm->end_data))
		if (current->brk_randomized)
		min_brk = mm->start_brk;
		else
		min_brk = mm->end_data;

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