From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-189.mta0.migadu.com (out-189.mta0.migadu.com [91.218.175.189]) (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 616CA27FD52 for ; Tue, 29 Jul 2025 23:13:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.189 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753830796; cv=none; b=JvxO69fItJuQGpUk5rvdr/5/AGcu/DMC26efLzsujd+y3m1BFYVuiCwolO+nfN5I57XF9D6uFTNKsWelwVYsE1bID+MBH2LW6WE+7mF0WT4sxL24f8clmKYArtJiNQ6w3hkY+zWeZI5phd02U6fEqWKL7zHJ8UPbD5HdDpbXLLM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753830796; c=relaxed/simple; bh=WxvGFF87EU5ki9LEBULBMG8gjNsmrJZkd22aGwiMvlk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ILJUoZZjL6gzJUlg/aDtolvtvMCpbfXWpMItbpq8SUcv5PWpKIlgDinbtR4QwL9G25bS3RJ70n5bKC3d6VZHKmfjJcwfesUk7Y6by0e+7r9E+csU6IaWOfW6i6kzsiODJJz9F6+ge8C5PFbNJA6YnxgUCONLomCpB/qasp3DIMo= 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=BiEAl4Qm; arc=none smtp.client-ip=91.218.175.189 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="BiEAl4Qm" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1753830792; 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=yjZl9PRQAkl316Uaa6TzM+hjGmhIkh7ZeU0G7I1jd4M=; b=BiEAl4Qm3PbuOsjicsutjMzchEM7XKBSfoLzdFyUpBR9uGvso774O5UyFJNIOtd2NwzlTT Bcic+Ln0G48LIKHqwWhrCKJ23M07E4r1AmTtIaFcd3/AKrVWpQ99+dyepcr85P1eTuC0WQ sUe6tM/IXZbQhTTvtgXsCgAFVqinD6E= Date: Tue, 29 Jul 2025 16:13:06 -0700 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next v3 3/4] bpf: add bpf_icmp_send_unreach cgroup_skb kfunc To: Mahe Tardy Cc: alexei.starovoitov@gmail.com, andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org, coreteam@netfilter.org, daniel@iogearbox.net, fw@strlen.de, john.fastabend@gmail.com, netdev@vger.kernel.org, netfilter-devel@vger.kernel.org, oe-kbuild-all@lists.linux.dev, pablo@netfilter.org, lkp@intel.com References: <202507270940.kXGmRbg5-lkp@intel.com> <20250728094345.46132-1-mahe.tardy@gmail.com> <20250728094345.46132-4-mahe.tardy@gmail.com> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 7/29/25 3:06 AM, Mahe Tardy wrote: > On Mon, Jul 28, 2025 at 06:05:26PM -0700, Martin KaFai Lau wrote: >> On 7/28/25 2:43 AM, Mahe Tardy wrote: >>> This is needed in the context of Tetragon to provide improved feedback >>> (in contrast to just dropping packets) to east-west traffic when blocked >>> by policies using cgroup_skb programs. >>> >>> This reuse concepts from netfilter reject target codepath with the >>> differences that: >>> * Packets are cloned since the BPF user can still return SK_PASS from >>> the cgroup_skb progs and the current skb need to stay untouched >> >> This needs more details. Which field(s) of the skb are changed by the kfunc, >> the skb_dst_set in ip[6]_route_reply_fetch_dst() and/or the code path in the >> icmp[v6]_send() ? > > Okay I can add that: "ip[6]_route_reply_fetch_dst set the dst of the skb > by using the saddr as a daddr and routing it", I don't think > icmp[v6]_send touches the skb? I also don't think icmp[v6]_send touches the skb. I am still not sure if ip[6]_route_reply_fetch_dst is needed. > >> >>> (cgroup_skb hooks only allow read-only skb payload). >>> * Since cgroup_skb programs are called late in the stack, checksums do >>> not need to be computed or verified, and IPv4 fragmentation does not >>> need to be checked (ip_local_deliver should take care of that >>> earlier). >>> >>> Signed-off-by: Mahe Tardy >>> --- >>> net/core/filter.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++ >>> 1 file changed, 61 insertions(+) >>> >>> diff --git a/net/core/filter.c b/net/core/filter.c >>> index 7a72f766aacf..050872324575 100644 >>> --- a/net/core/filter.c >>> +++ b/net/core/filter.c >>> @@ -85,6 +85,10 @@ >>> #include >>> #include >>> #include >>> +#include >>> +#include >>> +#include >>> +#include >>> >>> #include "dev.h" >>> >>> @@ -12148,6 +12152,53 @@ __bpf_kfunc int bpf_sock_ops_enable_tx_tstamp(struct bpf_sock_ops_kern *skops, >>> return 0; >>> } >>> >>> +__bpf_kfunc int bpf_icmp_send_unreach(struct __sk_buff *__skb, int code) >>> +{ >>> + struct sk_buff *skb = (struct sk_buff *)__skb; >>> + struct sk_buff *nskb; >>> + >>> + switch (skb->protocol) { >>> + case htons(ETH_P_IP): >>> + if (code < 0 || code > NR_ICMP_UNREACH) >>> + return -EINVAL; >>> + >>> + nskb = skb_clone(skb, GFP_ATOMIC); >>> + if (!nskb) >>> + return -ENOMEM; >>> + >>> + if (ip_route_reply_fetch_dst(nskb) < 0) { >>> + kfree_skb(nskb); >>> + return -EHOSTUNREACH; >>> + } >>> + >>> + icmp_send(nskb, ICMP_DEST_UNREACH, code, 0); >>> + kfree_skb(nskb); >>> + break; >>> +#if IS_ENABLED(CONFIG_IPV6) >>> + case htons(ETH_P_IPV6): >>> + if (code < 0 || code > ICMPV6_REJECT_ROUTE) >>> + return -EINVAL; >>> + >>> + nskb = skb_clone(skb, GFP_ATOMIC); >>> + if (!nskb) >>> + return -ENOMEM; >>> + >>> + if (ip6_route_reply_fetch_dst(nskb) < 0) { >> >> From a very quick look at icmpv6_send(), it does its own route lookup. I >> haven't looked at the v4 yet. >> >> I am likely missing some details. Can you explain why it needs to do a >> lookup before calling icmpv6_send()? > > From my understanding, I need to do this to invert the daddr with the > saddr to send the unreach message back to the sender. From looking at how fl6.{daddr,saddr} are filled and passed to icmpv6_route_lookup in icmpv6_send(), the icmpv6_send() should have done the reverse/invert route lookup. I also don't see icmpv6_send uses the skb_dst() of the original skb. Did I misread the code? The kfunc does not work without ip[6]_route_reply_fetch_dst()? Again, I have not checked the v4 icmp_send. fwiw, the selftest should have both v4 and v6 test. Note that at cgroup/egress, the skb->_skb_refdst should have been set. The same should be true for cgroup/ingress for inet proto but it seems BPF_CGROUP_RUN_PROG_"INET"_INGRESS is not called from INET only now. e.g. sk_filter() can be called from af_netlink. It seems like there is a bug. > >> >>> + kfree_skb(nskb); >>> + return -EHOSTUNREACH; >>> + } >>> + >>> + icmpv6_send(nskb, ICMPV6_DEST_UNREACH, code, 0); >>> + kfree_skb(nskb); >>> + break; >>> +#endif >>> + default: >>> + return -EPROTONOSUPPORT; >>> + } >>> + >>> + return SK_DROP; >>> +} >>> + >