From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) (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 9A98B327C13 for ; Tue, 19 May 2026 14:34:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779201253; cv=none; b=mQUPLHNZBuEhwpWbeAw+Az20eRYUCqsmmQL/xAqcY6rA6Htr5DqlnszLPi4vllU8ttNlAmUyVTKBEKVNrS1QiI1rArRWjx+X7mRUALo+3dr5Uig788aXzIkUVmtcZhqGG1lqCRGkY8zpHL3+wiHK3TW9Mm2fNcDbBZT7NSdeyfQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779201253; c=relaxed/simple; bh=t0nm6yuJ4/fW0ep/fbPuMz2fS9oPQlBGHwa/WaGMkzk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Vg6mnXgect/vxL08WQpg0C6q1x+UEMb+rvHS9ki2n+8Nxnvdd4c+c2/hE+ziZDoLZma7VXyVRxRfmO+6HYKycoSKh5bHu1oSvjcTEqdZrdVJoXltfbnOQjcgBRxS0q7OKduQRQSQcPYfI3AQNpWT0jAQIhTTggls1zPVcwvH1vA= 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=YsP80veW; arc=none smtp.client-ip=91.218.175.181 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="YsP80veW" Message-ID: <546f713a-679c-40c5-b231-30ba274fac8a@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1779201248; 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=Z8tzOeJHN5d3IIEtNIth2aA1jXODL8qBco/DpqxAnmY=; b=YsP80veW1GSN2x5KVDR5ci4WvszEEde7saLwX2T89DkyuERWpuOZnRntRi+mjcIPJFuWVy JNQxCmZ2RdIzW3dR9nYlhrdX6K1Ds6XAP7+PlHlu2XSRT5y/bIvo2wBGrWLv/qXiWYOMbl elzNgM4i/uwAx+cOgVVYsF3VxpBcmM8= Date: Tue, 19 May 2026 22:33:53 +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> <7da4fc46-0432-4f3d-b1bb-1691a2464df0@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 On 5/19/26 10:15 PM, Phil Sutter wrote: > On Tue, May 19, 2026 at 06:50:55PM +0800, Jiayuan Chen wrote: > [...] >> 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. > Seems legit! I missed that one because most examples in net/ipv6/route.c > use a non-RCU variant, I guess because exclusive access is ensured via > other means. > >> 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. > I'd submit the _rcu fix in an initial patch of the series, so the one > introducing the fib6_nsiblings check extends correct code (using _rcu) > with a correct pattern (READ_ONCE). > > Thanks, Phil Got it - will respin as v2. Sending after a short cool-down. Respect