From: Jiri Kosina <[email protected]> 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 <[email protected]> Tested-by: Geert Uytterhoeven <[email protected]> Reported-by: Geert Uytterhoeven <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]> --- fs/binfmt_elf.c | 6 +++++- include/linux/sched.h | 3 +++ mm/mmap.c | 2 +- 3 files changed, 9 insertions(+), 2 deletions(-) diff -puN fs/binfmt_elf.c~brk-compat_brk-fix-detection-of-randomized-brk fs/binfmt_elf.c --- a/fs/binfmt_elf.c~brk-compat_brk-fix-detection-of-randomized-brk +++ a/fs/binfmt_elf.c @@ -941,9 +941,13 @@ static int load_elf_binary(struct linux_ 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 -puN include/linux/sched.h~brk-compat_brk-fix-detection-of-randomized-brk include/linux/sched.h --- a/include/linux/sched.h~brk-compat_brk-fix-detection-of-randomized-brk +++ a/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 -puN mm/mmap.c~brk-compat_brk-fix-detection-of-randomized-brk mm/mmap.c --- a/mm/mmap.c~brk-compat_brk-fix-detection-of-randomized-brk +++ a/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; _ _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
