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 3C37EC433EF for ; Wed, 25 May 2022 18:33:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343741AbiEYSdp (ORCPT ); Wed, 25 May 2022 14:33:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47734 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343668AbiEYSdn (ORCPT ); Wed, 25 May 2022 14:33:43 -0400 Received: from mail-il1-f200.google.com (mail-il1-f200.google.com [209.85.166.200]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5CDCCB2243 for ; Wed, 25 May 2022 11:33:42 -0700 (PDT) Received: by mail-il1-f200.google.com with SMTP id g11-20020a056e021e0b00b002d1b5e8389bso5524639ila.2 for ; Wed, 25 May 2022 11:33:42 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:date:in-reply-to:message-id:subject :from:to:cc; bh=3LlA84a/shawwGbR9ADlhr9ClWSvap2W3MAcAR6xg8Y=; b=VDYbCNl6kelFvH1dl47OLoZL7UAnHPcewg+47v8BbUwI6Zd5EO1w/6MtV6bmaB2zLp tY70A8ccplkEY/3faltwFIBSw4AErG5TJ0fBpOMrYKTD3AdqNls5P18d3EP3g0OenWd0 X8nZX/jYqjDkUc8EnK39wijgtVDKEBeLXUlfEeL9+Sm6r6kRJjoRYUtw950Vm8++2y+M dTFcOIKNfH1zSAskGtENDD/yLHYBN72ujeMtxGxfWy1fEWnfHCF2yHk0BsN4vMMZeSnU vJyL5r2g+/bcICbdAkHBrvKYbjuEjoEhYQURj89c3Ojp9Mz5i1I9XmePjQI70oJkGxu6 IMcw== X-Gm-Message-State: AOAM532RfWdffWqLfX4w8PLbp2E0GObpvxlp7Udqog1PX80W7ac3GBDg V7RycmkRPyA/cQAq12Oa6EEk5F7H0Tye3Lu+DzhLhNHlsKDT X-Google-Smtp-Source: ABdhPJwWD6CehZmGOUJFH/NGAkaozrOXWy/L6yb3NhEbFRBjSMW8lzjCVIVxul6oWoBnMYu3Q+l23mplGwhDmB8/vHSwanpPbBy4 MIME-Version: 1.0 X-Received: by 2002:a92:cd83:0:b0:2d1:8475:2f4d with SMTP id r3-20020a92cd83000000b002d184752f4dmr13420747ilb.229.1653503621753; Wed, 25 May 2022 11:33:41 -0700 (PDT) Date: Wed, 25 May 2022 11:33:41 -0700 In-Reply-To: X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <00000000000002766a05dfda5023@google.com> Subject: Re: [syzbot] KASAN: use-after-free Read in do_sync_mmap_readahead From: syzbot To: Matthew Wilcox Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, willy@infradead.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Wed, May 25, 2022 at 06:57:55PM +0100, Matthew Wilcox wrote: >> >> Ohh, that makes sense. We unlocked the mmap_sem, so the file is >> pinned, but the VMA isn't. I'll whip up a patch. > > #syz test want 2 args (repo, branch), got 7 > > From 01a4917c4cfe400eb310eba4f2fa466d381623c1 Mon Sep 17 00:00:00 2001 > From: "Matthew Wilcox (Oracle)" > Date: Wed, 25 May 2022 14:23:45 -0400 > Subject: [PATCH] mm/filemap: Cache the value of vm_flags > > After we have unlocked the mmap_lock for I/O, the file is pinned, but > the VMA is not. Checking this flag after that can be a use-after-free. > It's not a terribly interesting use-after-free as it can only read one > bit, and it's used to decide whether to read 2MB or 4MB. But it > upsets the automated tools and it's generally bad practice anyway, > so let's fix it. > > Reported-by: syzbot+5b96d55e5b54924c77ad@syzkaller.appspotmail.com > Fixes: 4687fdbb805a ("mm/filemap: Support VM_HUGEPAGE for file mappings") > Signed-off-by: Matthew Wilcox (Oracle) > --- > mm/filemap.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/mm/filemap.c b/mm/filemap.c > index 9a1eef6c5d35..61dd39990fda 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -2991,11 +2991,12 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) > struct address_space *mapping = file->f_mapping; > DEFINE_READAHEAD(ractl, file, ra, mapping, vmf->pgoff); > struct file *fpin = NULL; > + unsigned long vm_flags = vmf->vma->vm_flags; > unsigned int mmap_miss; > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > /* Use the readahead code, even if readahead is disabled */ > - if (vmf->vma->vm_flags & VM_HUGEPAGE) { > + if (vm_flags & VM_HUGEPAGE) { > fpin = maybe_unlock_mmap_for_io(vmf, fpin); > ractl._index &= ~((unsigned long)HPAGE_PMD_NR - 1); > ra->size = HPAGE_PMD_NR; > @@ -3003,7 +3004,7 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) > * Fetch two PMD folios, so we get the chance to actually > * readahead, unless we've been told not to. > */ > - if (!(vmf->vma->vm_flags & VM_RAND_READ)) > + if (!(vm_flags & VM_RAND_READ)) > ra->size *= 2; > ra->async_size = HPAGE_PMD_NR; > page_cache_ra_order(&ractl, ra, HPAGE_PMD_ORDER); > @@ -3012,12 +3013,12 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) > #endif > > /* If we don't want any read-ahead, don't bother */ > - if (vmf->vma->vm_flags & VM_RAND_READ) > + if (vm_flags & VM_RAND_READ) > return fpin; > if (!ra->ra_pages) > return fpin; > > - if (vmf->vma->vm_flags & VM_SEQ_READ) { > + if (vm_flags & VM_SEQ_READ) { > fpin = maybe_unlock_mmap_for_io(vmf, fpin); > page_cache_sync_ra(&ractl, ra->ra_pages); > return fpin; > -- > 2.34.1 >