From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Borkmann Subject: Re: [PATCH] filter: introduce SKF_AD_VLAN_PROTO BPF extension Date: Thu, 05 Mar 2015 21:03:12 +0100 Message-ID: <54F8B680.4050307@iogearbox.net> References: <1425501718-12066-1-git-send-email-msekleta@redhat.com> <54F77336.7040006@plumgrid.com> <20150305103715.GA3432@morgoth.brq.redhat.com> <54F889EB.7000203@plumgrid.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, Jiri Pirko , guy@alum.mit.edu, atzm@stratosphere.co.jp To: Alexei Starovoitov , Michal Sekletar Return-path: Received: from www62.your-server.de ([213.133.104.62]:59265 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752983AbbCEUDS (ORCPT ); Thu, 5 Mar 2015 15:03:18 -0500 In-Reply-To: <54F889EB.7000203@plumgrid.com> Sender: netdev-owner@vger.kernel.org List-ID: On 03/05/2015 05:52 PM, Alexei Starovoitov wrote: > On 3/5/15 2:37 AM, Michal Sekletar wrote: >> On Wed, Mar 04, 2015 at 01:03:50PM -0800, Alexei Starovoitov wrote: >>> On 3/4/15 12:41 PM, Michal Sekletar wrote: >>>> This commit introduces new BPF extension. It makes possible to load value of >>>> skb->vlan_proto (vlan tpid) to register A. >>>> >>>> Currently, vlan header is removed from frame and information is available to >>>> userspace only via tpacket interface. Hence, it is not possible to install >>>> filter which uses value of vlan tpid field. >>>> >>>> AFAICT only way how to filter based on tpid value is to reconstruct original >>>> frame encapsulation and interpret BPF filter code in userspace. Doing that is >>>> way slower than doing filtering in kernel. >>>> >>>> Cc: Alexei Starovoitov >>>> Cc: Jiri Pirko >>>> Signed-off-by: Michal Sekletar >>>> --- >>>> @@ -282,6 +282,7 @@ Possible BPF extensions are shown in the following table: >>>> vlan_tci skb_vlan_tag_get(skb) >>>> vlan_pr skb_vlan_tag_present(skb) >>>> rand prandom_u32() >>>> + vlan_proto skb->vlan_proto >>> >>> the patch is correct and looks clean, but I don't understand >>> the motivation for the patch. >> >> Way how libpcap currently uses BPF extensions is not compatible with old >> behavior where actual value of tpid field was checked. I wanted to address >> that, i.e. if "vlan" keyword is used as filter expression, libpcap should >> install a filter such that only ethernet frames having tpid value of 0x8100 or >> 0x9100 will pass. That is not the case with current libpcap git and 4.0-rc1 >> kernel. >> >> Given that I broke libpcap as described above I tried to come up with the way >> how to fix that. However I realized that with recent kernels there is no other >> way than adding new BPF extension. >> >>> There is already SKF_AD_VLAN_TAG_PRESENT. If it is set then only >>> two possible values of vlan_proto are ETH_P_8021Q or ETH_P_8021AD. >> >> Any reason why ETH_P_QINQ1, ETH_P_QINQ2, ETH_P_QINQ3 no longer works? If I >> understand correctly, you are basically saying, that there is no point checking >> for vlan tpid because PF_PACKET socket will never receive frame having other >> tpid value than above two anyway. >> >> So bottom line is that I wanted to grant userspace programs more flexibility, >> and you are saying that it is pointless because for example if outer tpid is >> 0x9100 socket will never receive the frame. If that is the case then >> disregard the patch. > > steering towards vlan device happens only for ETH_P_8021Q and > ETH_P_8021AD. Non-standard 0x9100 and other tags won't be popped into > skb metadata and will stay as-is in the packet body. > If the meaning of 'vlan 100' in libpcap is to detect all possible > vlan tpid then bpf program would need to check VLAN_TAG_PRESENT > (that would mean vlan_proto is either 0x8100 or 0x88A8) > and parse packet body for tpids 0x9[123]00. > Whether we add access to skb->vlan_proto or not, the program would > still need to do the above steps, but instead of checking for > vlan_tag_present only, it would need to do vlan_proto==0x8100 > or vlan_proto=0x88a8 and then parse the packet for tpid=0x9[123]00 > so adding access to vlan_proto will not simplify libpcap job. +1, libpcap would, of course, need to check for both, the offloaded and non-offloaded case. I'm not sure if you're already doing this or plan to fix it there, Michal? > At this point I think it's up to Dave to decide whether we need > this patch (after fixing the issue pointed by Denis) or not. > imo there is a benefit of giving programs more visibility into > skb metadata. I'm not really a big fan of it, but given we added commit a0cdfcf39362 ("packet: deliver VLAN TPID to userspace") to packet sockets ... Michal, please make sure in v2 that you Cc related JIT people. In case you're sending v2, please fix up bpf_asm in the following way: I don't like the vlan_{pr,proto} ... it's confusing, so lets add a better alias and keep compatibility with vlan_pr. Here's the chunk: diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt index 9930ecfb..d9a2080 100644 --- a/Documentation/networking/filter.txt +++ b/Documentation/networking/filter.txt @@ -279,8 +279,9 @@ Possible BPF extensions are shown in the following table: hatype skb->dev->type rxhash skb->hash cpu raw_smp_processor_id() + vlan_avail skb_vlan_tag_present(skb) vlan_tci skb_vlan_tag_get(skb) - vlan_pr skb_vlan_tag_present(skb) + vlan_proto skb->vlan_proto rand prandom_u32() These extensions can also be prefixed with '#'. diff --git a/tools/net/bpf_exp.l b/tools/net/bpf_exp.l index 833a966..c1a1a39 100644 --- a/tools/net/bpf_exp.l +++ b/tools/net/bpf_exp.l @@ -90,8 +90,10 @@ extern void yyerror(const char *str); "#"?("hatype") { return K_HATYPE; } "#"?("rxhash") { return K_RXHASH; } "#"?("cpu") { return K_CPU; } -"#"?("vlan_tci") { return K_VLANT; } "#"?("vlan_pr") { return K_VLANP; } +"#"?("vlan_avail") { return K_VLANP; } +"#"?("vlan_tci") { return K_VLANT; } +"#"?("vlan_proto") { return K_VLANPR; } "#"?("rand") { return K_RAND; } ":" { return ':'; } diff --git a/tools/net/bpf_exp.y b/tools/net/bpf_exp.y index e6306c5..d4c749c 100644 --- a/tools/net/bpf_exp.y +++ b/tools/net/bpf_exp.y @@ -56,7 +56,7 @@ static void bpf_set_jmp_label(char *label, enum jmp_type type); %token OP_LDXI %token K_PKT_LEN K_PROTO K_TYPE K_NLATTR K_NLATTR_NEST K_MARK K_QUEUE K_HATYPE -%token K_RXHASH K_CPU K_IFIDX K_VLANT K_VLANP K_POFF K_RAND +%token K_RXHASH K_CPU K_IFIDX K_VLANT K_VLANP K_VLANPR K_POFF K_RAND %token ':' ',' '[' ']' '(' ')' 'x' 'a' '+' 'M' '*' '&' '#' '%' @@ -167,6 +167,9 @@ ldb | OP_LDB K_RAND { bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0, SKF_AD_OFF + SKF_AD_RANDOM); } + | OP_LDB K_VLANPR { + bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0, + SKF_AD_OFF + SKF_AD_VLAN_PROTO); } ; ldh @@ -218,6 +221,9 @@ ldh | OP_LDH K_RAND { bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0, SKF_AD_OFF + SKF_AD_RANDOM); } + | OP_LDH K_VLANPR { + bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0, + SKF_AD_OFF + SKF_AD_VLAN_PROTO); } ; ldi @@ -274,6 +280,9 @@ ld | OP_LD K_RAND { bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0, SKF_AD_OFF + SKF_AD_RANDOM); } + | OP_LD K_VLANPR { + bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0, + SKF_AD_OFF + SKF_AD_VLAN_PROTO); } | OP_LD 'M' '[' number ']' { bpf_set_curr_instr(BPF_LD | BPF_MEM, 0, 0, $4); } | OP_LD '[' 'x' '+' number ']' {