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 19569EB64DA for ; Wed, 5 Jul 2023 13:03:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230453AbjGENDk (ORCPT ); Wed, 5 Jul 2023 09:03:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57008 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229493AbjGENDj (ORCPT ); Wed, 5 Jul 2023 09:03:39 -0400 Received: from Chamillionaire.breakpoint.cc (Chamillionaire.breakpoint.cc [IPv6:2a0a:51c0:0:237:300::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3D81FDA; Wed, 5 Jul 2023 06:03:38 -0700 (PDT) Received: from fw by Chamillionaire.breakpoint.cc with local (Exim 4.92) (envelope-from ) id 1qH2AS-0006HS-Pv; Wed, 05 Jul 2023 15:03:36 +0200 Date: Wed, 5 Jul 2023 15:03:36 +0200 From: Florian Westphal To: Thadeu Lima de Souza Cascardo Cc: netfilter-devel@vger.kernel.org, netdev@vger.kernel.org, Pablo Neira Ayuso Subject: Re: [PATCH] netfilter: nf_tables: prevent OOB access in nft_byteorder_eval Message-ID: <20230705130336.GD3751@breakpoint.cc> References: <20230705121515.747251-1-cascardo@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230705121515.747251-1-cascardo@canonical.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org Thadeu Lima de Souza Cascardo wrote: > When evaluating byteorder expressions with size 2, a union with 32-bit and > 16-bit members is used. Since the 16-bit members are aligned to 32-bit, > the array accesses will be out-of-bounds. > > It may lead to a stack-out-of-bounds access like the one below: Yes, this is broken. > Using simple s32 and s16 pointers for each of these accesses fixes the > problem. I'm not sure this is correct. Its certainly less wrong of course. > Fixes: 96518518cc41 ("netfilter: add nftables") > Cc: stable@vger.kernel.org > Reported-by: Tanguy DUBROCA (@SidewayRE) from @Synacktiv working with ZDI > Signed-off-by: Thadeu Lima de Souza Cascardo > --- > net/netfilter/nft_byteorder.c | 17 ++++++++++------- > 1 file changed, 10 insertions(+), 7 deletions(-) > > diff --git a/net/netfilter/nft_byteorder.c b/net/netfilter/nft_byteorder.c > index 9a85e797ed58..aa16bd2e92e2 100644 > --- a/net/netfilter/nft_byteorder.c > +++ b/net/netfilter/nft_byteorder.c > @@ -30,11 +30,14 @@ void nft_byteorder_eval(const struct nft_expr *expr, > const struct nft_byteorder *priv = nft_expr_priv(expr); > u32 *src = ®s->data[priv->sreg]; > u32 *dst = ®s->data[priv->dreg]; > - union { u32 u32; u16 u16; } *s, *d; > + u32 *s32, *d32; > + u16 *s16, *d16; > unsigned int i; > > - s = (void *)src; > - d = (void *)dst; > + s32 = (void *)src; > + d32 = (void *)dst; > + s16 = (void *)src; > + d16 = (void *)dst; > > switch (priv->size) { > case 8: { > @@ -62,11 +65,11 @@ void nft_byteorder_eval(const struct nft_expr *expr, > switch (priv->op) { > case NFT_BYTEORDER_NTOH: > for (i = 0; i < priv->len / 4; i++) > - d[i].u32 = ntohl((__force __be32)s[i].u32); > + d32[i] = ntohl((__force __be32)s32[i]); > break; > case NFT_BYTEORDER_HTON: > for (i = 0; i < priv->len / 4; i++) > - d[i].u32 = (__force __u32)htonl(s[i].u32); > + d32[i] = (__force __u32)htonl(s32[i]); > break; Ack, this looks better, but I'd just use src[i] and dst[i] rather than the weird union pointers the original has. > @@ -74,11 +77,11 @@ void nft_byteorder_eval(const struct nft_expr *expr, > switch (priv->op) { > case NFT_BYTEORDER_NTOH: > for (i = 0; i < priv->len / 2; i++) > - d[i].u16 = ntohs((__force __be16)s[i].u16); > + d16[i] = ntohs((__force __be16)s16[i]); This on the other hand... I'd say this should mimic what the 64bit case is doing and use nft_reg_store16() nft_reg_load16() helpers for the register accesses. something like: for (i = 0; i < priv->len / 2; i++) { v16 = nft_reg_load16(&src[i]); nft_reg_store16(&dst[i], + ntohs((__force __be16)v16)); } [ not even compile tested ] Same for the htons case. On a slightly related note, some of the nftables test cases create bogus conversions, e.g.: # src/nft --debug=netlink add rule ip6 t c 'ct mark set ip6 dscp << 2 | # 0x10' ip6 t c [ payload load 2b @ network header + 0 => reg 1 ] [ bitwise reg 1 = ( reg 1 & 0x0000c00f ) ^ 0x00000000 ] [ bitwise reg 1 = ( reg 1 >> 0x00000006 ) ] [ byteorder reg 1 = ntoh(reg 1, 2, 1) ] // NO-OP! should be reg 1, 2, 2) I presume? I'd suggest to add a patch for nf-next that rejects such crap.