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 X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 71ADFC169C4 for ; Thu, 31 Jan 2019 10:51:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 373F6218AC for ; Thu, 31 Jan 2019 10:51:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548931919; bh=D2ByF8ztCPvkuYmo+MsVePh1McUSZHsVaWZmqonFVek=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=ODcaL61p1iWKfL1zw5YdEOXwMPDmvd404JvZEozGkuDmdjpeXviRw9NMpC/DB83rG 5/QALxejwTxkDWac6na1vMILJWlt/xK2yhPx0q8zFmhQIOTJ36xwb1ZV7pltGXNm8H S4r/s41S3DbgyBzqUjB6HPxAtcPh626Lu7n/YyFM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728454AbfAaKv5 (ORCPT ); Thu, 31 Jan 2019 05:51:57 -0500 Received: from mail.kernel.org ([198.145.29.99]:57094 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726462AbfAaKv5 (ORCPT ); Thu, 31 Jan 2019 05:51:57 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 65CC8218AC; Thu, 31 Jan 2019 10:51:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548931915; bh=D2ByF8ztCPvkuYmo+MsVePh1McUSZHsVaWZmqonFVek=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=NVawc4R23PVaTNSEYMswGqRq9G5ZoJS6MvHrYx4CvE0YnEIBeEfWt41uxo9c05Ywc ZtH2H0o3GFj7l1mvSbb7nwKlHjjrhaKk6vUH+dxki4YnLe/dSWSLgAntm1c4QGMcPF vJ+AzSuxRQU0jaN+4PpZSCoMeK4YL5IOdpO21Q2Q= Date: Thu, 31 Jan 2019 11:51:52 +0100 From: Greg KH To: Kees Cook Cc: Andrew Morton , syzbot , Eric Biggers , Souptick Joarder , LKML , David Rientjes , syzkaller-bugs Subject: Re: general protection fault in relay_open_buf Message-ID: <20190131105152.GB13686@kroah.com> References: <00000000000074cbc30580b16bc3@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.2 (2019-01-07) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 31, 2019 at 10:54:18PM +1300, Kees Cook wrote: > On Thu, Jan 31, 2019 at 7:53 AM syzbot > wrote: > > > > Hello, > > > > syzbot found the following crash on: > > > > HEAD commit: 02495e76ded5 Add linux-next specific files for 20190130 > > git tree: linux-next > > console output: https://syzkaller.appspot.com/x/log.txt?x=12cf10df400000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=a2b2e9c0bc43c14d > > dashboard link: https://syzkaller.appspot.com/bug?extid=16c3a70e1e9b29346c43 > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13266698c00000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1715bb64c00000 > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > Reported-by: syzbot+16c3a70e1e9b29346c43@syzkaller.appspotmail.com > > > > kasan: CONFIG_KASAN_INLINE enabled > > kasan: GPF could be caused by NULL-ptr deref or user memory access > > general protection fault: 0000 [#1] PREEMPT SMP KASAN > > CPU: 0 PID: 8092 Comm: syz-executor405 Not tainted 5.0.0-rc4-next-20190130 > > #22 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > > Google 01/01/2011 > > RIP: 0010:relay_set_buf_dentry kernel/relay.c:412 [inline] > > static inline void relay_set_buf_dentry(struct rchan_buf *buf, > struct dentry *dentry) > { > buf->dentry = dentry; > d_inode(buf->dentry)->i_size = buf->early_bytes; <-- > } > > Doing a bisect landed on this: > > ff9fb72bc07705c00795ca48631f7fffe24d2c6b ("debugfs: return error > values, not NULL") > > If I revert this patch, I can't reproduce any more. I don't see a > relationship, though... > > My crash appears as: > [ 121.934378] BUG: unable to handle kernel NULL pointer dereference > at 0000000000000047 > [ 121.937187] #PF error: [normal kernel read fault] > [ 121.938824] PGD 800000041f699067 P4D 800000041f699067 PUD 42d08f067 PMD 0 > [ 121.941166] Oops: 0000 [#1] SMP PTI > [ 121.942381] CPU: 2 PID: 3134 Comm: relay Not tainted > 5.0.0-rc4-next-20190130 #1020 > [ 121.943873] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), > BIOS 1.10.2-1ubuntu1 04/01/2014 > [ 121.945395] RIP: 0010:relay_open_buf.part.10+0x2b8/0x330 > ... > [ 121.960021] Call Trace: > [ 121.960453] relay_open+0x18e/0x2c0 > [ 121.961070] __blk_trace_setup+0x1af/0x350 > [ 121.961777] blk_trace_ioctl+0x93/0x100 > > > $ ./scripts/faddr2line vmlinux relay_open_buf.part.10+0x2b8/0x330 > relay_open_buf.part.10+0x2b8/0x330: > relay_set_buf_dentry at kernel/relay.c:412 > (inlined by) relay_open_buf at kernel/relay.c:458 > > So it's the same location, but not sure about 0x47 offset. d_inode is > 0x58 from dentry. And i_size is 0x50 from inode. If this isn't NULL, > but rather an ERR_PTR, the errno is either: > > EBADF 9 Bad file descriptor > EEXIST 17 File exists > > Neither are used in the debugfs patch, but debugfs is clearly used in > do_blk_trace_setup(): > > if (!blk_debugfs_root) > return -ENOENT; > ... > dir = debugfs_lookup(buts->name, blk_debugfs_root); > if (!dir) > bt->dir = dir = debugfs_create_dir(buts->name, > blk_debugfs_root); > if (!dir) > goto err; > ... > bt->rchan = relay_open("trace", dir, buts->buf_size, > buts->buf_nr, &blk_relay_callbacks, bt); > > Which is confirmed by the next line in my traceback: > > $ ./scripts/faddr2line vmlinux __blk_trace_setup+0x1af/0x350 > __blk_trace_setup+0x1af/0x350: > do_blk_trace_setup at kernel/trace/blktrace.c:534 > (inlined by) __blk_trace_setup at kernel/trace/blktrace.c:577 Can you test the patch below? thanks, greg k-h -------------- diff --git a/kernel/relay.c b/kernel/relay.c index 04f248644e06..9e0f52375487 100644 --- a/kernel/relay.c +++ b/kernel/relay.c @@ -428,6 +428,8 @@ static struct dentry *relay_create_buf_file(struct rchan *chan, dentry = chan->cb->create_buf_file(tmpname, chan->parent, S_IRUSR, buf, &chan->is_global); + if (IS_ERR(dentry)) + dentry = NULL; kfree(tmpname); @@ -461,7 +463,7 @@ static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu) dentry = chan->cb->create_buf_file(NULL, NULL, S_IRUSR, buf, &chan->is_global); - if (WARN_ON(dentry)) + if (IS_ERR_OR_NULL(dentry)) goto free_buf; }