From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-185.mta0.migadu.com (out-185.mta0.migadu.com [91.218.175.185]) (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 D87CD1AC443 for ; Wed, 28 Aug 2024 21:29:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.185 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724880570; cv=none; b=k6XbBRl7dsNvEQdHe18Oeih3/+TqUBYlTbzE8I932yUS8zDaeCK4xVVy8wc2Bjyy+UwxenPjipXMX/AW+zjk4A+RDDT46MeOFZ3ftE43sC4dL6a/RIorMfTMViOgRMglpqO0O11rcKxteGZ9Srf6cJSxqdaLz8rtQDNBzNblkTg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724880570; c=relaxed/simple; bh=9sCPNmtAPxcbhDCTFFWA/8fBdfOsdaWBtBNT+bFXAWk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GT/2KjvHaWrnTiJdpjpyv7/OmRRC/mYBab+ckiC8fB33/e5H6S9k/5OYuVZA2WAJhZbv0z8GGjvdpD73qB6txNQO6jbZt+Flzw2aLuBNzBkqmhtZv+ZL/pXStkCdi23nG3em92+ZUPNrxSm7lupqVBvymfZP5VjN5i1+cS61Jtw= 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=gm11JTZb; arc=none smtp.client-ip=91.218.175.185 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="gm11JTZb" Message-ID: <5186a69b-c53d-4afa-b3be-e6bd272d264f@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1724880565; 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=eyljCDOX50IlTeH4bxvhhXlTuF5KPs/h7kPstVhqUDY=; b=gm11JTZbtLS91Yl2PR37OiViGVtxJ5SBwzkQu4/PbCu+9WRHDulRILdzHdbDvWjjEU5sc2 /8GqgOskcaacVxCrko20e4WKX+/oUhBokkNU/EBAHselMoAtgkEifavSRjWsrORU8hljj3 sdAYoFRHY6W0FBdu8wdu8I3CwgSMDLo= Date: Wed, 28 Aug 2024 14:29:17 -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 v2 1/2] bpf: tcp: prevent bpf_reserve_hdr_opt() from growing skb larger than MTU To: zijianzhang@bytedance.com, Amery Hung , bpf@vger.kernel.org Cc: edumazet@google.com, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, dsahern@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, mykolal@fb.com, shuah@kernel.org, xiyou.wangcong@gmail.com, wangdongdong.6@bytedance.com, zhoufeng.zf@bytedance.com References: <20240827013736.2845596-1-zijianzhang@bytedance.com> <20240827013736.2845596-2-zijianzhang@bytedance.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau Content-Language: en-US In-Reply-To: <20240827013736.2845596-2-zijianzhang@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 8/26/24 6:37 PM, zijianzhang@bytedance.com wrote: > From: Amery Hung > > This series prevents sockops users from accidentally causing packet > drops. This can happen when a BPF_SOCK_OPS_HDR_OPT_LEN_CB program > reserves different option lengths in tcp_sendmsg(). > > Initially, sockops BPF_SOCK_OPS_HDR_OPT_LEN_CB program will be called to > reserve a space in tcp_send_mss(), which will return the MSS for TSO. > Then, BPF_SOCK_OPS_HDR_OPT_LEN_CB will be called in __tcp_transmit_skb() > again to calculate the actual tcp_option_size and skb_push() the total > header size. > > skb->gso_size is restored from TCP_SKB_CB(skb)->tcp_gso_size, which is > derived from tcp_send_mss() where we first call HDR_OPT_LEN. If the > reserved opt size is smaller than the actual header size, the len of the > skb can exceed the MTU. As a result, ip(6)_fragment will drop the > packet if skb->ignore_df is not set. > > To prevent this accidental packet drop, we need to make sure the > second call to the BPF_SOCK_OPS_HDR_OPT_LEN_CB program reserves space > not more than the first time. iiuc, it is a bug in the bpf prog itself that did not reserve the same header length and caused a drop. It is not the only drop case though for an incorrect bpf prog. There are other cases where a bpf prog can accidentally drop a packet. Do you have an actual use case that the bpf prog cannot reserve the correct header length for the same sk ?