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 ED14FEB64DD for ; Thu, 29 Jun 2023 03:57:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231615AbjF2D5w (ORCPT ); Wed, 28 Jun 2023 23:57:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43774 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232047AbjF2D52 (ORCPT ); Wed, 28 Jun 2023 23:57:28 -0400 Received: from outgoing.mit.edu (outgoing-auth-1.mit.edu [18.9.28.11]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 36A052724 for ; Wed, 28 Jun 2023 20:57:23 -0700 (PDT) Received: from cwcc.thunk.org (pool-173-48-117-150.bstnma.fios.verizon.net [173.48.117.150]) (authenticated bits=0) (User authenticated as tytso@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id 35T3vFjH012677 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 28 Jun 2023 23:57:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mit.edu; s=outgoing; t=1688011037; bh=/B8OaI8xdxY2/ixF7cPiltqwMuMLhwgslkQoAhheftU=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=UzYyGrCC7DvV69tgz6T2gHwlRJM5qg1CvOb/CX9+Ih8HXtCpAgwr9z/JG5zYJ6hvN 5zaRJ9UYwuxZnbcnOMQSLjptkjrSs99kdqod/Y/O8f5i71iDGmLU4kgCK55SbwpLcN qg8CdFi/gZQxw1KmoNLaM+t5OJ9eZEe3L4qI2aV83t/15gf03Ln3Su9U2mXVCFsYbx nSst3tqbAB0bfh9Il4yK2x3ytAEexWl4ouZeD5m5Yammq9jdKNls0xqRLwIBbH7wZj csjcFVoVw/mLhY6EtCKlL+V8LPhE8SDVbPVEKYpP+naG1X3d74a1qasdkVbOIVAc5L bF76yvSJYip5Q== Received: by cwcc.thunk.org (Postfix, from userid 15806) id EBEDC15C027F; Wed, 28 Jun 2023 23:57:14 -0400 (EDT) Date: Wed, 28 Jun 2023 23:57:14 -0400 From: "Theodore Ts'o" To: syzbot Cc: adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [ext4?] general protection fault in ext4_put_io_end_defer Message-ID: <20230629035714.GJ8954@mit.edu> References: <0000000000002a0b1305feeae5db@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0000000000002a0b1305feeae5db@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org #syz set subsystems: crypto On Sat, Jun 24, 2023 at 07:21:44PM -0700, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: f7efed9f38f8 Add linux-next specific files for 20230616 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=152e89f3280000 > kernel config: https://syzkaller.appspot.com/x/.config?x=60b1a32485a77c16 > dashboard link: https://syzkaller.appspot.com/bug?extid=94a8c779c6b238870393 > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=116af1eb280000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14e22d2f280000 If you look at the reproducer, it's creating an AF_ALG (algorithm) socket and messing with it. This is easier to see in the syz reproducer, but you can see exactly what it's doing in the C reproducer above: # https://syzkaller.appspot.com/bug?id=4ee7656695de92cbd5820111379ae0698af0f475 # See https://goo.gl/kgGztJ for information about syzkaller reproducers. #{"threaded":true,"repeat":true,"procs":1,"slowdown":1,"sandbox":"none","sandbox_arg":0,"netdev":true,"binfmt_misc":true,"close_fds":true,"vhci":true,"ieee802154":true,"sysctl":true,"swap":true,"tmpdir":true} r0 = socket$alg(0x26, 0x5, 0x0) bind$alg(r0, &(0x7f0000000280)={0x26, 'hash\x00', 0x0, 0x0, 'sha3-256-generic\x00'}, 0x58) r1 = accept4(r0, 0x0, 0x0, 0x0) recvmmsg$unix(r1, &(0x7f0000003700)=[{{0x0, 0x700, 0x0}}], 0x600, 0x0, 0x0) sendmsg$can_bcm(r1, &(0x7f0000000180)={0x0, 0x0, &(0x7f0000000140)={0x0}}, 0x400c800) (0x26 is 38, or AF_ALG) >From looking at the stack trace, it looks like this is triggering a coredump, which presumably is the ext4 write that triggers the GPF in ext4_put_io_end_defer. But given that the syz and C reproducer isn't doing anything ext4 related at all, and it's purely trying to use the AF_ALG socket to calculate SHA3 in the kernel (and the greek chorus cries out, "WHY?"[1]), I'm going to send this over to the crypto folks to investigate. Cheers, - Ted [1] TIL that AF_ALG exists. Inquiring minds want to know: * Why do we expose the AF_ALG userspace interface? * Who uses it? * Why do they use it? * Is there a CONFIG option to disable it in the name of decreasing the attack surface of the kernel? * If not, should we add one? :-)