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=-11.4 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 A0E79C388F9 for ; Mon, 26 Oct 2020 22:40:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5F00E216FD for ; Mon, 26 Oct 2020 22:40:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="v55KPbIz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394632AbgJZWko (ORCPT ); Mon, 26 Oct 2020 18:40:44 -0400 Received: from mail-lf1-f65.google.com ([209.85.167.65]:41479 "EHLO mail-lf1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2394618AbgJZWkn (ORCPT ); Mon, 26 Oct 2020 18:40:43 -0400 Received: by mail-lf1-f65.google.com with SMTP id 126so3195646lfi.8 for ; Mon, 26 Oct 2020 15:40:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=p5mpdK7QEfDL5slMiMMuatEPuKSHdDFbWljAr9yhKWI=; b=v55KPbIzkQ6XpCeJxtQgHmpkBNNN3Vy4h0+4aIkEH2igYiZnH3CJAMrDuHf4tTQvx5 +wXxRLMS9dNA15/QVPY7OUGem1hJkBceu7Qdttdve4KhzOvZExMdsVKYf6MXC5q5nBxM ISMeVIjjKOUupiKOaEUrZycc/H68pAdqeHFEeGIWgKeX/aVznb3gEMTl0+pY3SlQwmhL 4P0OPOFRSDesfWW6znsYcdBpbch5cxisQWglfrmvWLm7vAWsovJGRlypeM3gwYPgCVsJ Iz2407lA5bXQ2uYEgM/3LbzxpmTCudk6S2cEF3eN8yhmyvi0FvkkcZ22BJTwAtCS1z+8 VgWg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=p5mpdK7QEfDL5slMiMMuatEPuKSHdDFbWljAr9yhKWI=; b=qWhBYnlayfBhv/DbBm8nwUjmhvpeMHqIZXjz98S+QGsmTzs4ZHKCVAE+ZzihlB4Mrx e4+AxBAq9/TZlihAQ/OuKs1ba79zSKlkysrJJK6cfDOl49d8LSB1vJQVwQx76PXq6+1b 7qXkxQZpeaJkox5KpbUO0IkCMPJIYag5RuSIHZ5TH2XuynzeMmUkfyzDm1UEgjw5u0/t G3YqtfklcHPwvbYNTt/g7xmy5n3Ga7u3Vcg8GsCb47NmRxChSOB3B4WFjVV9+TDGeZZa xmyAYdrVyegagfmrgV1SoFzmwwCgcgMkMumpwwWpArYsgM+nIWmADISw/JQU4g1C1cVJ 5P+Q== X-Gm-Message-State: AOAM5323ehLCWo+74pOG3puV2YJzv/EIOKSududuOZwIBICM0qxvpP8J nAzF/AZW0uH/0CjbrAInElqOUAEPdFUs+wWaHhgCkw== X-Google-Smtp-Source: ABdhPJxjFDjWOwRZrKpaQ7DfqAb76Wdq0EnB5RBSKFjRVQvhEwDyFBnOIEaqJQyewYmpprB2TRhB0ucxFKBwT21u16o= X-Received: by 2002:a05:6512:52f:: with SMTP id o15mr5593174lfc.381.1603752038729; Mon, 26 Oct 2020 15:40:38 -0700 (PDT) MIME-Version: 1.0 References: <20201026200715.170261-1-ebiggers@kernel.org> <20201026215658.GA185792@sol.localdomain> In-Reply-To: <20201026215658.GA185792@sol.localdomain> From: Jann Horn Date: Mon, 26 Oct 2020 23:40:12 +0100 Message-ID: Subject: Re: [PATCH] crypto: af_alg - avoid undefined behavior accessing salg_name To: Eric Biggers 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 Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 26, 2020 at 10:57 PM Eric Biggers wrote: > 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). Ugh, of course you're right, sorry. > 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... Eh, I think there'd probably be bigger issues with that elsewhere. > > > 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)`. Sorry, I've been unusually unconcentrated today. Sorry about the noise, ignore what I said.