From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-177.mta0.migadu.com (out-177.mta0.migadu.com [91.218.175.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DA1F1370AFE for ; Tue, 19 May 2026 10:51:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779187874; cv=none; b=WX7U97/bqhTplobM53osBlMJ8BxYRXWH3suO8xKMXG0jdXGk130lWKs5eIvR5uaf4wdwIQK3BtHbx1uptTRmb39IyfPMeVr4U2lAFPP/xDwH2XDsVlq8slMx8qKs4cQG62mCj5Dz4nUkR1H+88PimUdytOIramzhqGfHjWE2ZNg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779187874; c=relaxed/simple; bh=PeEBkY1CNEPFKSe/J0NkWerJVO/X3uLmpZrY5tgvokc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jihBEOmW4rDeGNlTx+SNIXYFrfCppULlKxpwbW6i7HStMjOhAJRkEbHxuctdNUgFQgRSXNCqJ94Gj8EnYpybpt2K2RX6GZA141NMeSV8jmfeisHMzNfJR99uo9zrV3Aav+455cxSIxnFly6k2pTM9AcwT22zsnabrp5qpWp55rM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=AqgsO/gI; arc=none smtp.client-ip=91.218.175.177 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="AqgsO/gI" Message-ID: <7da4fc46-0432-4f3d-b1bb-1691a2464df0@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1779187864; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=H8n96lsxRVIrD96zj1R14KLDTBGb0m6IdyBe3EwkwOg=; b=AqgsO/gIZYY4FYs0BfjjDO+MQ/FWrl5Bofi7ORUY9Xq5Y6Rx5MsbreLBRfGsrngqNLWUAE 9wF61thTfoHbGjg40zzwDq+kTzQlH2bh9wgrYBZV6dAMDMwkOU8lEWYr6TXEXB9HeOrud/ bxK5Wxa2a8CHNF88TKGtiZeel5kiNiE= Date: Tue, 19 May 2026 18:50:55 +0800 Precedence: bulk X-Mailing-List: netfilter-devel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH nf 1/2] netfilter: nft_fib_ipv6: handle routes via external nexthop To: Phil Sutter Cc: netfilter-devel@vger.kernel.org, pablo@netfilter.org, fw@strlen.de, coreteam@netfilter.org References: <20260519041431.396218-1-jiayuan.chen@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Jiayuan Chen In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Hi Phil, Thanks for your review. On 5/19/26 6:08 PM, Phil Sutter wrote: > Hi, > > On Tue, May 19, 2026 at 12:14:30PM +0800, Jiayuan Chen wrote: >> fib6_info has a union: >> >> union { >> struct list_head fib6_siblings; >> struct list_head nh_list; >> }; >> >> Old-style multipath (ip -6 route add ... nexthop ... nexthop ...) uses >> fib6_siblings. External nexthop (ip -6 route add ... nhid N) uses >> nh_list, linked into &nh->f6i_list. >> >> nft_fib6_info_nh_uses_dev() blindly walks &rt->fib6_siblings, causing >> an OOB read past the struct nexthop slab when rt->nh is set: >> >> ================================================================== >> BUG: KASAN: slab-out-of-bounds in nft_fib6_eval+0x1362/0x16c0 >> Read of size 8 at addr ffff888103a099d0 by task ping/386 >> >> CPU: 2 UID: 0 PID: 386 Comm: ping Not tainted 7.1.0-rc3+ #251 PREEMPT >> Call Trace: >> >> dump_stack_lvl+0x76/0xa0 >> print_report+0xd1/0x5f0 >> kasan_report+0xe7/0x130 >> __asan_report_load8_noabort+0x14/0x30 >> nft_fib6_eval+0x1362/0x16c0 >> nft_do_chain+0x279/0x18c0 >> nft_do_chain_ipv6+0x1a8/0x230 >> nf_hook_slow+0xad/0x200 >> ipv6_rcv+0x152/0x380 >> __netif_receive_skb_one_core+0x118/0x1c0 >> ================================================================== >> >> Branch by route shape: when rt->nh is set, walk via >> nexthop_for_each_fib6_nh() (also covers nh groups, which the original >> code missed); otherwise walk fib6_siblings, guarded by fib6_nsiblings. >> >> Fixes: 1c32b24c234b ("netfilter: nft_fib_ipv6: switch to fib6_lookup") >> Signed-off-by: Jiayuan Chen >> --- >> net/ipv6/netfilter/nft_fib_ipv6.c | 16 ++++++++++++++++ >> 1 file changed, 16 insertions(+) >> >> diff --git a/net/ipv6/netfilter/nft_fib_ipv6.c b/net/ipv6/netfilter/nft_fib_ipv6.c >> index 8b2dba88ee96..a44919f46de9 100644 >> --- a/net/ipv6/netfilter/nft_fib_ipv6.c >> +++ b/net/ipv6/netfilter/nft_fib_ipv6.c >> @@ -160,16 +160,32 @@ static bool nft_fib6_info_nh_dev_match(const struct net_device *nh_dev, >> l3mdev_master_ifindex_rcu(nh_dev) == dev->ifindex; >> } >> >> +static int nft_fib6_nh_match_dev_cb(struct fib6_nh *nh, void *arg) >> +{ >> + const struct net_device *dev = arg; >> + >> + return nft_fib6_info_nh_dev_match(nh->fib_nh_dev, dev) ? 1 : 0; > Why the ternary here? The function returns bool, but the iterator merely > checks the value for 0 and caller returns the value as bool as well. > >> +} >> + >> static bool nft_fib6_info_nh_uses_dev(struct fib6_info *rt, >> const struct net_device *dev) >> { >> const struct net_device *nh_dev; >> struct fib6_info *iter; >> >> + /* External nexthop: fib6_siblings slot aliases nh_list, walk via nh. */ >> + if (rt->nh) >> + return nexthop_for_each_fib6_nh(rt->nh, >> + nft_fib6_nh_match_dev_cb, >> + (void *)dev) != 0; All make sense ! >> + >> nh_dev = fib6_info_nh_dev(rt); >> if (nft_fib6_info_nh_dev_match(nh_dev, dev)) >> return true; >> >> + if (!rt->fib6_nsiblings) > Should this access using READ_ONCE() as per commit 31d7d67ba127 ("ipv6: > annotate data-races around rt->fib6_nsiblings")? You are right, we need READ_ONCE since fib6_add_rt2node will modify @fib6_nsiblings . >> + return false; >> + >> list_for_each_entry(iter, &rt->fib6_siblings, fib6_siblings) { Now I think we should also change list_for_each_entry  into list_for_each_entry_rcu for the same reason. But I'm not sure whether it is appropriate or not since this patch target to commit in Fiexes tag. May be a followup patch is necessary. >> nh_dev = fib6_info_nh_dev(iter); > I thought about open-coding this to void the need for the callback > wrapper, but it's not worth it. > > Cheers, Phil