On Fri, Jul 7, 2017 at 11:57 AM, Kees Cook <keesc...@chromium.org> wrote: > To avoid pathological stack usage or the need to special-case setuid > execs, just limit all arg stack usage to at most _STK_LIM / 4 * 3 (6MB).
Ok, this I think I should just apply, but would prefer to avoid multi-line complex conditionals around things like this. So how about the attached slightly edited version instead? I didn't test it (and I'm not really committing it until I get an ack or two), but it seemed all ObviouslyCorrect(tm). FamousLastWords(tm). Comments? Linus
From 4f677953627bc64393bcc310f4f779282a089ae3 Mon Sep 17 00:00:00 2001 From: Kees Cook <keesc...@chromium.org> Date: Fri, 7 Jul 2017 11:57:29 -0700 Subject: [PATCH] exec: Limit arg stack to at most 75% of _STK_LIM To avoid pathological stack usage or the need to special-case setuid execs, just limit all arg stack usage to at most 75% of _STK_LIM (6MB). Signed-off-by: Kees Cook <keesc...@chromium.org> Signed-off-by: Linus Torvalds <torva...@linux-foundation.org> --- fs/exec.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 904199086490..62175cbcc801 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -220,8 +220,7 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, if (write) { unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start; - unsigned long ptr_size; - struct rlimit *rlim; + unsigned long ptr_size, limit; /* * Since the stack will hold pointers to the strings, we @@ -250,14 +249,16 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, return page; /* - * Limit to 1/4-th the stack size for the argv+env strings. + * Limit to 1/4 of the max stack size or 3/4 of _STK_LIM + * (whichever is smaller) for the argv+env strings. * This ensures that: * - the remaining binfmt code will not run out of stack space, * - the program will have a reasonable amount of stack left * to work from. */ - rlim = current->signal->rlim; - if (size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) + limit = _STK_LIM / 4 * 3; + limit = min(limit, rlimit(RLIMIT_STACK) / 4); + if (size > limit) goto fail; } -- 2.13.1.518.g0d864c4df