From 4471a675dfc7ca676c165079e91c712b09dc9ce4 Mon Sep 17 00:00:00 2001 From: Jiri Kosina Date: Thu, 14 Apr 2011 15:22:09 -0700 Subject: [PATCH] brk: COMPAT_BRK: fix detection of randomized brk 5520e89 ("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 Tested-by: Geert Uytterhoeven Reported-by: Geert Uytterhoeven Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/binfmt_elf.c | 6 +++++- include/linux/sched.h | 3 +++ mm/mmap.c | 2 +- 3 files changed, 9 insertions(+), 2 deletions(-) diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index f34078d702d..303983fabfd 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -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) { diff --git a/include/linux/sched.h b/include/linux/sched.h index 4ec2c027e92..18d63cea284 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -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 diff --git a/mm/mmap.c b/mm/mmap.c index 8c05e5b43b6..e27e0cf0de0 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -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; -- 2.20.1