From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 501E4C433EF for ; Thu, 17 Feb 2022 20:51:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243369AbiBQUvR (ORCPT ); Thu, 17 Feb 2022 15:51:17 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:53942 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231586AbiBQUvP (ORCPT ); Thu, 17 Feb 2022 15:51:15 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6A083163D75 for ; Thu, 17 Feb 2022 12:51:00 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 076BDB81B0E for ; Thu, 17 Feb 2022 20:50:59 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D19DFC340E8; Thu, 17 Feb 2022 20:50:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1645131057; bh=M3DCGGewZr70eOjOG2Q+HAYxvOudSciSqV1kblBNK10=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=CGhuRuGZUgReF4FrJXds7xwuu7lZPVgEWg6FkVnzGeppquRnxl8H1BlU/gNxN5YhW 0R/EB451JzKtQlDEOcOa1lQyMr2VqCnuo8J+uq64RhvnpYkTxur4uAanC15/ruRL+G PLoADDOvAC4+tSBvui4R4PEP+ncpLCTe41J82m1I= Date: Thu, 17 Feb 2022 12:50:56 -0800 From: Andrew Morton To: Suren Baghdasaryan Cc: Michal Hocko , shy828301@gmail.com, rientjes@google.com, willy@infradead.org, hannes@cmpxchg.org, guro@fb.com, riel@surriel.com, minchan@kernel.org, kirill@shutemov.name, aarcange@redhat.com, brauner@kernel.org, christian@brauner.io, hch@infradead.org, oleg@redhat.com, david@redhat.com, jannh@google.com, shakeelb@google.com, luto@kernel.org, christian.brauner@ubuntu.com, fweimer@redhat.com, jengelh@inai.de, timmurray@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com, syzbot+2ccf63a4bd07cf39cab0@syzkaller.appspotmail.com Subject: Re: [PATCH 1/1] mm: fix use-after-free bug when mm->mmap is reused after being freed Message-Id: <20220217125056.df4073b42f2d911c99939e93@linux-foundation.org> In-Reply-To: References: <20220215201922.1908156-1-surenb@google.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 17 Feb 2022 11:51:13 -0800 Suren Baghdasaryan wrote: > This changelog is very detailed and I support switching to it. Andrew, > please let me know if I should re-post the patch with this description > or you will just amend the one in your tree. I have made that change. From: Suren Baghdasaryan Subject: mm: fix use-after-free bug when mm->mmap is reused after being freed oom reaping (__oom_reap_task_mm) relies on a 2 way synchronization with exit_mmap. First it relies on the mmap_lock to exclude from unlock path[1], page tables tear down (free_pgtables) and vma destruction. This alone is not sufficient because mm->mmap is never reset. For historical reasons[2] the lock is taken there is also MMF_OOM_SKIP set for oom victims before. The oom reaper only ever looks at oom victims so the whole scheme works properly but process_mrelease can opearate on any task (with fatal signals pending) which doesn't really imply oom victims. That means that the MMF_OOM_SKIP part of the synchronization doesn't work and it can see a task after the whole address space has been demolished and traverse an already released mm->mmap list. This leads to use after free as properly caught up by KASAN report. Fix the issue by reseting mm->mmap so that MMF_OOM_SKIP synchronization is not needed anymore. The MMF_OOM_SKIP is not removed from exit_mmap yet but it acts mostly as an optimization now. [1] 27ae357fa82b ("mm, oom: fix concurrent munlock and oom reaper unmap, v3") [2] 212925802454 ("mm: oom: let oom_reap_task and exit_mmap run concurrently") [mhocko@suse.com: changelog rewrite] Link: https://lore.kernel.org/all/00000000000072ef2c05d7f81950@google.com/ Link: https://lkml.kernel.org/r/20220215201922.1908156-1-surenb@google.com Fixes: 64591e8605d6 ("mm: protect free_pgtables with mmap_lock write lock in exit_mmap") Signed-off-by: Suren Baghdasaryan Reported-by: syzbot+2ccf63a4bd07cf39cab0@syzkaller.appspotmail.com Suggested-by: Michal Hocko Reviewed-by: Rik van Riel Reviewed-by: Yang Shi Acked-by: Michal Hocko Cc: David Rientjes Cc: Matthew Wilcox Cc: Johannes Weiner Cc: Roman Gushchin Cc: Rik van Riel Cc: Minchan Kim Cc: Kirill A. Shutemov Cc: Andrea Arcangeli Cc: Christian Brauner Cc: Christoph Hellwig Cc: Oleg Nesterov Cc: David Hildenbrand Cc: Jann Horn Cc: Shakeel Butt Cc: Andy Lutomirski Cc: Christian Brauner Cc: Florian Weimer Cc: Jan Engelhardt Cc: Tim Murray Signed-off-by: Andrew Morton --- mm/mmap.c | 1 + 1 file changed, 1 insertion(+) --- a/mm/mmap.c~mm-fix-use-after-free-bug-when-mm-mmap-is-reused-after-being-freed +++ a/mm/mmap.c @@ -3186,6 +3186,7 @@ void exit_mmap(struct mm_struct *mm) vma = remove_vma(vma); cond_resched(); } + mm->mmap = NULL; mmap_write_unlock(mm); vm_unacct_memory(nr_accounted); } _