From f823e36f5f92b087b6cbc304b371004bd1cb8f17 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Fri, 7 Jul 2017 11:57:29 -0700 Subject: [PATCH] exec: Limit arg stack to at most 75% of _STK_LIM commit da029c11e6b12f321f36dac8771e833b65cec962 upstream. 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 Signed-off-by: Linus Torvalds [bwh: Backported to 3.16: replaced code is slightly different] Signed-off-by: Ben Hutchings CVE-2018-14634 Signed-off-by: Kevin F. Haggerty Change-Id: If678301ef4bfa8f7d54716a222768ee80330b3aa --- fs/exec.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index c607edcc97d..e730485bb18 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -207,8 +207,7 @@ 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 @@ -237,14 +236,16 @@ 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 > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) + limit = _STK_LIM / 4 * 3; + limit = min(limit, rlimit(RLIMIT_STACK) / 4); + if (size > limit) goto fail; }