Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 1d3d0f8b authored by Kees Cook's avatar Kees Cook Committed by Greg Kroah-Hartman
Browse files

fs/exec.c: account for argv/envp pointers 

commit 98da7d08850fb8bdeb395d6368ed15753304aa0c upstream.

When limiting the argv/envp strings during exec to 1/4 of the stack limit,
the storage of the pointers to the strings was not included.  This means
that an exec with huge numbers of tiny strings could eat 1/4 of the stack
limit in strings and then additional space would be later used by the
pointers to the strings.

For example, on 32-bit with a 8MB stack rlimit, an exec with 1677721
single-byte strings would consume less than 2MB of stack, the max (8MB /
4) amount allowed, but the pointers to the strings would consume the
remaining additional stack space (1677721 * 4 == 6710884).

The result (1677721 + 6710884 == 8388605) would exhaust stack space
entirely.  Controlling this stack exhaustion could result in
pathological behavior in setuid binaries (CVE-2017-1000365).

[akpm@linux-foundation.org: additional commenting from Kees]
Fixes: b6a2fea3 ("mm: variable length argument support")
Link: http://lkml.kernel.org/r/20170622001720.GA32173@beast


Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Qualys Security Advisory <qsa@qualys.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 22da7ca8

fs/exec.c

+24 −4
Original line number Diff line number Diff line
@@ -206,8 +206,26 @@ 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;



		/*

		 * Since the stack will hold pointers to the strings, we

		 * must account for them as well.

		 *

		 * The size calculation is the entire vma while each arg page is

		 * built, so each time we get here it's calculating how far it

		 * is currently (rather than each call being just the newly

		 * added size from the arg page).  As a result, we need to

		 * always add the entire size of the pointers, so that on the

		 * last call to get_arg_page() we'll actually have the entire

		 * correct size.

		 */

		ptr_size = (bprm->argc + bprm->envc) * sizeof(void *);

		if (ptr_size > ULONG_MAX - size)

			goto fail;

		size += ptr_size;



		acct_arg_size(bprm, size / PAGE_SIZE);



		/*
@@ -225,13 +243,15 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, 
		 *    to work from.

		 */

		rlim = current->signal->rlim;

		if (size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) {

			put_page(page);

			return NULL;

		}

		if (size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4)

			goto fail;

	}



	return page;



fail:

	put_page(page);

	return NULL;

}



static void put_arg_page(struct page *page)