From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (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 31022154B4 for ; Mon, 11 Sep 2023 18:08:40 +0000 (UTC) Received: from out-210.mta0.migadu.com (out-210.mta0.migadu.com [IPv6:2001:41d0:1004:224b::d2]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 05C8C106 for ; Mon, 11 Sep 2023 11:08:38 -0700 (PDT) Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1694455717; 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=UvfTrJqC5ZVvRjuLgp5olVGxg/zOhnCEu+HKmrCSMbY=; b=IKZPxMNYA8rerDahaGEh4uUT+02JXQM5e806P8QBTAtoKiQ38hX5obRaRKghRy6M5aRSXO Zirzz8RXzPNQV9U/nZUdAl3rTGfX/5cjLHrsrQ7p+ZTkxXpoWMJ7bjdJrQ0Xavjorr1MEU OVSjtgw2k6rwQasQy+IIQdGIXjb9iRg= Date: Mon, 11 Sep 2023 11:08:30 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next 1/2] bpf: return correct -ENOBUFS from bpf_clone_redirect To: Daniel Borkmann , Stanislav Fomichev Cc: ast@kernel.org, andrii@kernel.org, song@kernel.org, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, haoluo@google.com, jolsa@kernel.org, bpf@vger.kernel.org References: <20230908210007.1469091-1-sdf@google.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: 8bit X-Migadu-Flow: FLOW_OUT X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_BLOCKED, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On 9/11/23 10:23 AM, Daniel Borkmann wrote: > On 9/11/23 7:11 PM, Stanislav Fomichev wrote: >> On 09/09, Martin KaFai Lau wrote: >>> On 9/8/23 2:00 PM, Stanislav Fomichev wrote: >>>> Commit 151e887d8ff9 ("veth: Fixing transmit return status for dropped >>>> packets") exposed the fact that bpf_clone_redirect is capable of >>>> returning raw NET_XMIT_XXX return codes. >>>> >>>> This is in the conflict with its UAPI doc which says the following: >>>> "0 on success, or a negative error in case of failure." >>>> >>>> Let's wrap dev_queue_xmit's return value (in __bpf_tx_skb) into >>>> net_xmit_errno to make sure we correctly propagate NET_XMIT_DROP >>>> as -ENOBUFS instead of 1. >>>> >>>> Note, this is technically breaking existing UAPI where we used to >>>> return 1 and now will do -ENOBUFS. The alternative is to >>>> document that bpf_clone_redirect can return 1 for DROP and 2 for CN. >>>> >>>> Reported-by: Daniel Borkmann >>>> Signed-off-by: Stanislav Fomichev >>>> --- >>>>    net/core/filter.c | 3 +++ >>>>    1 file changed, 3 insertions(+) >>>> >>>> diff --git a/net/core/filter.c b/net/core/filter.c >>>> index a094694899c9..9e297931b02f 100644 >>>> --- a/net/core/filter.c >>>> +++ b/net/core/filter.c >>>> @@ -2129,6 +2129,9 @@ static inline int __bpf_tx_skb(struct net_device *dev, >>>> struct sk_buff *skb) >>>>        ret = dev_queue_xmit(skb); >>>>        dev_xmit_recursion_dec(); >>>> +    if (ret > 0) >>>> +        ret = net_xmit_errno(ret); >>> >>> I think it is better to have bpf_clone_redirect returning -ENOBUFS instead >>> of leaking NET_XMIT_XXX to the uapi. The bpf_clone_redirect in the >>> uapi/bpf.h also mentions >>> >>>   *      Return >>>   *              0 on success, or a negative error in case of failure. >>> >>> If -ENOBUFS is returned in __bpf_tx_skb, should the same be done for >>> __bpf_rx_skb? and should net_xmit_errno() only be done for >>> bpf_clone_redirect()?  __bpf_{tx,rx}_skb is also used by skb_do_redirect() >>> which also calls __bpf_redirect_neigh() that returns NET_XMIT_xxx but no >>> caller seems to care the NET_XMIT_xxx value now. >> >> __bpf_rx_skb seems to only add to backlog and doesn't seem to return any >> of the NET_XMIT_xxx. But I might be wrong and haven't looked too deep >> into that. enqueue_to_backlog could return NET_RX_DROP which happens to have the same value as NET_XMIT_DROP. I think this will get propagated back to __bpf_rx_skb(). >> >>> Daniel should know more here. I would wait for Daniel to comment. >> >> Ack, sure! > > I think my preference would be to just document it in the helper UAPI, what > Stan was suggesting below: > > | Note, this is technically breaking existing UAPI where we used to > | return 1 and now will do -ENOBUFS. The alternative is to > | document that bpf_clone_redirect can return 1 for DROP and 2 for CN. > > And then only adjusting the test case. > > Programs checking for ret < 0 will continue to behave as before. Technically > the bpf_clone_redirect() did its job just that on the veth side things were > dropped. Other drivers such as tun, vrf, ipvlan, bond could already have > returned NET_XMIT_DROP, so technically it's not a new situation where it is > possible. And having a ret > 0 could then also be clearly used to differentiate > that something came from driver side rather than helper side. sure. sgtm. Not sure if it will be useful to spell out the >0 meaning in uapi/bpf.h. > >>> For the selftest, may be another option is to use a 28 bytes data_in for the >>> lwt program redirecting to veth? 14 bytes used by bpf_prog_test_run_skb and >>> leave 14 bytes for veth_xmit. It seems the original intention of the "veth >>> ETH_HLEN+1 packet ingress" test is expecting it to succeed also. >> >> IIUC, you're suggesting to pass full ipv4 or ipv6 packet for veth tests >> to make them actually succeed with the forwarding, right? >> >> Sure, I can do that. But let's keep this entry with the -NOBUFS as well? >> Just for the sake of ensuring that we don't export NET_XMIT_xxx from >> uapi. In that case it makes sense to only change the eth+1byte test case to expect >0 ret (or -ENOBUF as in patch 2, depending on the above discussion). No need to add an extra test.