From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f72.google.com (mail-pg0-f72.google.com [74.125.83.72]) by kanga.kvack.org (Postfix) with ESMTP id C5D60440846 for ; Thu, 24 Aug 2017 11:04:12 -0400 (EDT) Received: by mail-pg0-f72.google.com with SMTP id r11so4072506pgs.9 for ; Thu, 24 Aug 2017 08:04:12 -0700 (PDT) Received: from foss.arm.com (usa-sjc-mx-foss1.foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id q7si2958353pfi.408.2017.08.24.08.04.10 for ; Thu, 24 Aug 2017 08:04:10 -0700 (PDT) Date: Thu, 24 Aug 2017 16:02:49 +0100 From: Mark Rutland Subject: Re: [PATCH] fork: fix incorrect fput of ->exe_file causing use-after-free Message-ID: <20170824150110.GA29665@leverpostej> References: <20170823211408.31198-1-ebiggers3@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170823211408.31198-1-ebiggers3@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Eric Biggers Cc: linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org, Dmitry Vyukov , Ingo Molnar , Konstantin Khlebnikov , Michal Hocko , Oleg Nesterov , Peter Zijlstra , Vlastimil Babka , stable@vger.kernel.org, Eric Biggers On Wed, Aug 23, 2017 at 02:14:08PM -0700, Eric Biggers wrote: > From: Eric Biggers > > Commit 7c051267931a ("mm, fork: make dup_mmap wait for mmap_sem for > write killable") made it possible to kill a forking task while it is > waiting to acquire its ->mmap_sem for write, in dup_mmap(). However, it > was overlooked that this introduced an new error path before a reference > is taken on the mm_struct's ->exe_file. Since the ->exe_file of the new > mm_struct was already set to the old ->exe_file by the memcpy() in > dup_mm(), it was possible for the mmput() in the error path of dup_mm() > to drop a reference to ->exe_file which was never taken. This caused > the struct file to later be freed prematurely. > > Fix it by updating mm_init() to NULL out the ->exe_file, in the same > place it clears other things like the list of mmaps. > diff --git a/kernel/fork.c b/kernel/fork.c > index e075b7780421..cbbea277b3fb 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -806,6 +806,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p, > mm_init_cpumask(mm); > mm_init_aio(mm); > mm_init_owner(mm, p); > + RCU_INIT_POINTER(mm->exe_file, NULL); > mmu_notifier_mm_init(mm); > init_tlb_flush_pending(mm); > #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS I've been seeing similar issues on arm64 with use-after-free of a file and other memory corruption [1]. This patch seems to fix that; a test that normally fired in a few minutes has been happily running for hours with this applied. Thanks, Mark. [1] https://lkml.kernel.org/r/20170824113743.GA14737@leverpostej -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org