From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754602AbdJINHI (ORCPT ); Mon, 9 Oct 2017 09:07:08 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:42119 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754308AbdJIMpB (ORCPT ); Mon, 9 Oct 2017 08:45:01 -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, "Michal Hocko" , "Linus Torvalds" , "Oleg Nesterov" , "Hugh Dickins" , "Rik van Riel" , "Willy Tarreau" Date: Mon, 09 Oct 2017 13:44:24 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 101/192] mm/mmap.c: do not blow on PROT_NONE MAP_FIXED holes in the stack 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 3.16.49-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Michal Hocko commit 561b5e0709e4a248c67d024d4d94b6e31e3edf2f upstream. Commit 1be7107fbe18 ("mm: larger stack guard gap, between vmas") has introduced a regression in some rust and Java environments which are trying to implement their own stack guard page. They are punching a new MAP_FIXED mapping inside the existing stack Vma. This will confuse expand_{downwards,upwards} into thinking that the stack expansion would in fact get us too close to an existing non-stack vma which is a correct behavior wrt safety. It is a real regression on the other hand. Let's work around the problem by considering PROT_NONE mapping as a part of the stack. This is a gros hack but overflowing to such a mapping would trap anyway an we only can hope that usespace knows what it is doing and handle it propely. Fixes: 1be7107fbe18 ("mm: larger stack guard gap, between vmas") Link: http://lkml.kernel.org/r/20170705182849.GA18027@dhcp22.suse.cz Signed-off-by: Michal Hocko Debugged-by: Vlastimil Babka Cc: Ben Hutchings Cc: Willy Tarreau Cc: Oleg Nesterov Cc: Rik van Riel Cc: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Ben Hutchings --- mm/mmap.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2153,7 +2153,8 @@ int expand_upwards(struct vm_area_struct gap_addr = TASK_SIZE; next = vma->vm_next; - if (next && next->vm_start < gap_addr) { + if (next && next->vm_start < gap_addr && + (next->vm_flags & (VM_WRITE|VM_READ|VM_EXEC))) { if (!(next->vm_flags & VM_GROWSUP)) return -ENOMEM; /* Check that both stack segments have the same anon_vma? */ @@ -2233,7 +2234,8 @@ int expand_downwards(struct vm_area_stru if (gap_addr > address) return -ENOMEM; prev = vma->vm_prev; - if (prev && prev->vm_end > gap_addr) { + if (prev && prev->vm_end > gap_addr && + (prev->vm_flags & (VM_WRITE|VM_READ|VM_EXEC))) { if (!(prev->vm_flags & VM_GROWSDOWN)) return -ENOMEM; /* Check that both stack segments have the same anon_vma? */