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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 347DCC4363A for ; Mon, 26 Oct 2020 21:57:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DBDC321707 for ; Mon, 26 Oct 2020 21:57:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603749421; bh=R+obtcU/s4vSbo5rZODZBjaaAgLCDGZtwJiSZGh8KDk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=U8iwZkk8ulmFwKaODTKpiI1+da/DUFFcjcfDKBtPnOgp2G9/nQy5vBlkd6tr0e77N 3N2ZFN9UdbkU9EYSvW7XWLLJ26EY2MDWdwVR8XdIaXVT2Ov+Nx6e0W7f6asHuO8TYS 13o53jvWMP1+XIf5j/dzQRjQqUGOKvBlSrUax0lo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390914AbgJZV5B (ORCPT ); Mon, 26 Oct 2020 17:57:01 -0400 Received: from mail.kernel.org ([198.145.29.99]:54072 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390265AbgJZV5B (ORCPT ); Mon, 26 Oct 2020 17:57:01 -0400 Received: from sol.localdomain (172-10-235-113.lightspeed.sntcca.sbcglobal.net [172.10.235.113]) (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 481982084C; Mon, 26 Oct 2020 21:57:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603749420; bh=R+obtcU/s4vSbo5rZODZBjaaAgLCDGZtwJiSZGh8KDk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=R8xepUxVq/1oH7oTecTcsFE+/ejXfnm05vsSH+TJJwytUEdyvNtRMewUARFUPBtEY CDw6Dob0BpnHmZrnyTY3CbfSO+/K7Nx8JdTOSO1b9dHyaS2z7Et/o95SgPB+myYR13 P3Ugescy28F3uwfvh/0+dHZEDLjS1YFy+v1/urWA= Date: Mon, 26 Oct 2020 14:56:58 -0700 From: Eric Biggers To: Jann Horn Cc: "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" , Herbert Xu , syzkaller-bugs , linux-hardening@vger.kernel.org, Linux API , kernel list , Kees Cook , Elena Petrova , Vegard Nossum , "Gustavo A . R . Silva" , stable , syzbot Subject: Re: [PATCH] crypto: af_alg - avoid undefined behavior accessing salg_name Message-ID: <20201026215658.GA185792@sol.localdomain> References: <20201026200715.170261-1-ebiggers@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Mon, Oct 26, 2020 at 10:23:35PM +0100, 'Jann Horn' via syzkaller-bugs wrote: > On Mon, Oct 26, 2020 at 9:08 PM Eric Biggers wrote: > > Commit 3f69cc60768b ("crypto: af_alg - Allow arbitrarily long algorithm > > names") made the kernel start accepting arbitrarily long algorithm names > > in sockaddr_alg. > > That's not true; it's still limited by the size of struct > sockaddr_storage (128 bytes total for the entire address). Interesting, so the actual limit is 104 bytes. It seems like the intent of that commit was to make it unlimited, though... > If you make it longer, __copy_msghdr_from_user() will silently truncate the > size. That's used for sys_sendmsg(), which AFAICT isn't relevant here. sockaddr_alg is used with sys_bind(), which fails with EINVAL if the address is longer than sizeof(struct sockaddr_storage). However, since sys_sendmsg() is truncating overly-long addresses, it's probably the case that sizeof(struct sockaddr_storage) can never be increased in the future... > > > This is broken because the kernel can access indices >= 64 in salg_name, > > which is undefined behavior -- even though the memory that is accessed > > is still located within the sockaddr structure. It would only be > > defined behavior if the array were properly marked as arbitrary-length > > (either by making it a flexible array, which is the recommended way > > these days, or by making it an array of length 0 or 1). > > > > We can't simply change salg_name into a flexible array, since that would > > break source compatibility with userspace programs that embed > > sockaddr_alg into another struct, or (more commonly) declare a > > sockaddr_alg like 'struct sockaddr_alg sa = { .salg_name = "foo" };'. > > > > One solution would be to change salg_name into a flexible array only > > when '#ifdef __KERNEL__'. However, that would keep userspace without an > > easy way to actually use the longer algorithm names. > > > > Instead, add a new structure 'sockaddr_alg_new' that has the flexible > > array field, and expose it to both userspace and the kernel. > > Make the kernel use it correctly in alg_bind(). > [...] > > @@ -147,7 +147,7 @@ static int alg_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len) > > const u32 allowed = CRYPTO_ALG_KERN_DRIVER_ONLY; > > struct sock *sk = sock->sk; > > struct alg_sock *ask = alg_sk(sk); > > - struct sockaddr_alg *sa = (void *)uaddr; > > + struct sockaddr_alg_new *sa = (void *)uaddr; > > const struct af_alg_type *type; > > void *private; > > int err; > > @@ -155,7 +155,11 @@ static int alg_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len) > > if (sock->state == SS_CONNECTED) > > return -EINVAL; > > > > - if (addr_len < sizeof(*sa)) > > + BUILD_BUG_ON(offsetof(struct sockaddr_alg_new, salg_name) != > > + offsetof(struct sockaddr_alg, salg_name)); > > + BUILD_BUG_ON(offsetof(struct sockaddr_alg, salg_name) != sizeof(*sa)); > > + > > + if (addr_len < sizeof(*sa) + 1) > > return -EINVAL; > > > > /* If caller uses non-allowed flag, return error. */ > > @@ -163,7 +167,7 @@ static int alg_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len) > > return -EINVAL; > > > > sa->salg_type[sizeof(sa->salg_type) - 1] = 0; > > - sa->salg_name[sizeof(sa->salg_name) + addr_len - sizeof(*sa) - 1] = 0; > > + sa->salg_name[addr_len - sizeof(*sa) - 1] = 0; > > This looks like an out-of-bounds write in the case `addr_len == > sizeof(struct sockaddr_storage)`. I think you mean addr_len == sizeof(*sa)? That's what the 'if (addr_len < sizeof(*sa) + 1) return -EINVAL' above is for. - Eric