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 16F6BEB64DD for ; Fri, 30 Jun 2023 07:46:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232134AbjF3Hq2 (ORCPT ); Fri, 30 Jun 2023 03:46:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55410 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232357AbjF3HqZ (ORCPT ); Fri, 30 Jun 2023 03:46:25 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 42EE619B5; Fri, 30 Jun 2023 00:46:17 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id C55E0616EC; Fri, 30 Jun 2023 07:46:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DD814C433C8; Fri, 30 Jun 2023 07:46:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1688111176; bh=FEyFCEh9AVWYVR5/3aJ4Wq2M5vu3WP7EgYsC+YbQcXU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jCPcaVZGkOE/wdNx6lzkn6tm0El2fEy6PYCEevjGu10ZsFRHzHJIovamvvMhvarN3 dv6DXzwZsM9uCZ2/GuPATK9gFi3HWzOJUelhZHTHQ8+Z+3oMJUwElLTkaJqGfPzxcW 6fvQDdIEcZtfLGz8R/j1OSkPb5WsYABSiiggqMs9rVIMtiovXuHO5DgWWQl5ugx+ey dHus8JVOF8QMBRnF/UbmYu6zS7ln3hk8MajwN9rnazSba/PhUILtr//l0u/gvph2Bp CGEk4FKGFsziIaregYiPbwu1BXpv7jMp+ixpzIe+TUNWDIwz/7IkAy0a8XMJq1O6tm +knllFsylLZdQ== Date: Fri, 30 Jun 2023 00:46:14 -0700 From: Eric Biggers To: Theodore Ts'o Cc: syzbot , 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, David Howells Subject: Re: [syzbot] [ext4?] general protection fault in ext4_put_io_end_defer Message-ID: <20230630074614.GC36542@sol.localdomain> References: <0000000000002a0b1305feeae5db@google.com> <20230629035714.GJ8954@mit.edu> <20230630074111.GB36542@sol.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230630074111.GB36542@sol.localdomain> Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Fri, Jun 30, 2023 at 12:41:11AM -0700, Eric Biggers wrote: > On Wed, Jun 28, 2023 at 11:57:14PM -0400, Theodore Ts'o wrote: > > #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. > > Just a couple weeks ago, commit c662b043cdca ("crypto: af_alg/hash: Support > MSG_SPLICE_PAGES") had many syzbot reports against it. This particular report > is against next-20230616 which didn't include the fix commit b6d972f68983 > ("crypto: af_alg/hash: Fix recvmsg() after sendmsg(MSG_MORE)"). So there's a > high chance this report is no longer valid. I'll go ahead and invalidate it: > > #syz invalid > > > > > 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? :-) > > AF_ALG has existed since 2010. My understanding that its original purpose was > to expose hardware crypto accelerators to userspace. Unfortunately, support for > exposing *any* crypto algorithm was included as well, which IMO was a mistake. > > There are quite a few different userspace programs that use AF_ALG purely to get > at the CPU-based algorithm implementations, without any sort of intention to use > hardware crypto accelerator. Probably because it seemed "easy". Or "better" > because everything in the kernel is better, right? > > It's controlled by the CONFIG_CRYPTO_USER_API_* options, with the hash support > in particular controlled by CONFIG_CRYPTO_USER_API_HASH. Though good luck > disabling it on most systems, as systemd depends on it... > Actually it turns out systemd has finally seen the light: https://github.com/systemd/systemd/commit/2c3794f4228162c9bfd9e10886590d9f5b1920d7 - Eric