From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752890AbdF0LKo (ORCPT ); Tue, 27 Jun 2017 07:10:44 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:34800 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752685AbdF0LKU (ORCPT ); Tue, 27 Jun 2017 07:10:20 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Linus Torvalds" Date: Tue, 27 Jun 2017 12:09:36 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 1/4] mm: do not grow the stack vma just because of an overrun on preceding vma In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:6f00:88c8:c921:d332 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.90-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Linus Torvalds commit 09884964335e85e897876d17783c2ad33cf8a2e0 upstream. The stack vma is designed to grow automatically (marked with VM_GROWSUP or VM_GROWSDOWN depending on architecture) when an access is made beyond the existing boundary. However, particularly if you have not limited your stack at all ("ulimit -s unlimited"), this can cause the stack to grow even if the access was really just one past *another* segment. And that's wrong, especially since we first grow the segment, but then immediately later enforce the stack guard page on the last page of the segment. So _despite_ first growing the stack segment as a result of the access, the kernel will then make the access cause a SIGSEGV anyway! So do the same logic as the guard page check does, and consider an access to within one page of the next segment to be a bad access, rather than growing the stack to abut the next segment. Reported-and-tested-by: Heiko Carstens Signed-off-by: Linus Torvalds Signed-off-by: Ben Hutchings --- mm/mmap.c | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1802,9 +1802,28 @@ int expand_downwards(struct vm_area_stru return error; } +/* + * Note how expand_stack() refuses to expand the stack all the way to + * abut the next virtual mapping, *unless* that mapping itself is also + * a stack mapping. We want to leave room for a guard page, after all + * (the guard page itself is not added here, that is done by the + * actual page faulting logic) + * + * This matches the behavior of the guard page logic (see mm/memory.c: + * check_stack_guard_page()), which only allows the guard page to be + * removed under these circumstances. + */ #ifdef CONFIG_STACK_GROWSUP int expand_stack(struct vm_area_struct *vma, unsigned long address) { + struct vm_area_struct *next; + + address &= PAGE_MASK; + next = vma->vm_next; + if (next && next->vm_start == address + PAGE_SIZE) { + if (!(next->vm_flags & VM_GROWSUP)) + return -ENOMEM; + } return expand_upwards(vma, address); } @@ -1827,6 +1846,14 @@ find_extend_vma(struct mm_struct *mm, un #else int expand_stack(struct vm_area_struct *vma, unsigned long address) { + struct vm_area_struct *prev; + + address &= PAGE_MASK; + prev = vma->vm_prev; + if (prev && prev->vm_end == address) { + if (!(prev->vm_flags & VM_GROWSDOWN)) + return -ENOMEM; + } return expand_downwards(vma, address); }