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Commit 4471a675 authored by Jiri Kosina's avatar Jiri Kosina Committed by Linus Torvalds
Browse files

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: default avatarJiri Kosina <jkosina@suse.cz>
Tested-by: default avatarGeert Uytterhoeven <geert@linux-m68k.org>
Reported-by: default avatarGeert Uytterhoeven <geert@linux-m68k.org>
Cc: <stable@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus 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;