From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Borkmann Subject: Re: [V2 PATCH net-next 1/2] xdp: implement xdp_redirect_map for generic XDP Date: Fri, 08 Sep 2017 12:41:05 +0200 Message-ID: <59B273C1.9060806@iogearbox.net> References: <150478756604.28665.6915020425359475729.stgit@firesoul> <150478759310.28665.17184783248584070473.stgit@firesoul> <59B15334.4070103@iogearbox.net> <20170908103601.21cdecb2@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, "David S. Miller" , Daniel Borkmann , John Fastabend , Andy Gospodarek , alexei.starovoitov@gmail.com To: Jesper Dangaard Brouer Return-path: Received: from www62.your-server.de ([213.133.104.62]:52071 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753132AbdIHKlI (ORCPT ); Fri, 8 Sep 2017 06:41:08 -0400 In-Reply-To: <20170908103601.21cdecb2@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On 09/08/2017 10:36 AM, Jesper Dangaard Brouer wrote: > On Thu, 07 Sep 2017 16:09:56 +0200 > Daniel Borkmann wrote: >> On 09/07/2017 02:33 PM, Jesper Dangaard Brouer wrote: >>> Using bpf_redirect_map is allowed for generic XDP programs, but the >>> appropriate map lookup was never performed in xdp_do_generic_redirect(). >>> >>> Instead the map-index is directly used as the ifindex. For the >>> xdp_redirect_map sample in SKB-mode '-S', this resulted in trying >>> sending on ifindex 0 which isn't valid, resulting in getting SKB >>> packets dropped. Thus, the reported performance numbers are wrong in >>> commit 24251c264798 ("samples/bpf: add option for native and skb mode >>> for redirect apps") for the 'xdp_redirect_map -S' case. >>> >>> It might seem innocent this was lacking, but it can actually crash the >>> kernel. The potential crash is caused by not consuming redirect_info->map. >>> The bpf_redirect_map helper will set this_cpu_ptr(&redirect_info)->map >>> pointer, which will survive even after unloading the xdp bpf_prog and >>> deallocating the devmap data-structure. This leaves a dead map >>> pointer around. The kernel will crash when loading the xdp_redirect >>> sample (in native XDP mode) as it doesn't reset map (via bpf_redirect) >>> and returns XDP_REDIRECT, which will cause it to dereference the map >>> pointer. >>> >>> Fixes: 6103aa96ec07 ("net: implement XDP_REDIRECT for xdp generic") >>> Fixes: 24251c264798 ("samples/bpf: add option for native and skb mode for redirect apps") >>> Signed-off-by: Jesper Dangaard Brouer >>> --- >>> include/trace/events/xdp.h | 4 ++-- >>> net/core/filter.c | 14 +++++++++++--- >>> 2 files changed, 13 insertions(+), 5 deletions(-) >>> >>> diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h >>> index 862575ac8da9..4e16c43fba10 100644 >>> --- a/include/trace/events/xdp.h >>> +++ b/include/trace/events/xdp.h >>> @@ -138,11 +138,11 @@ DEFINE_EVENT_PRINT(xdp_redirect_template, xdp_redirect_map_err, >>> >>> #define _trace_xdp_redirect_map(dev, xdp, fwd, map, idx) \ >>> trace_xdp_redirect_map(dev, xdp, fwd ? fwd->ifindex : 0, \ >>> - 0, map, idx); >>> + 0, map, idx) >>> >>> #define _trace_xdp_redirect_map_err(dev, xdp, fwd, map, idx, err) \ >>> trace_xdp_redirect_map_err(dev, xdp, fwd ? fwd->ifindex : 0, \ >>> - err, map, idx); >>> + err, map, idx) >>> >>> #endif /* _TRACE_XDP_H */ >>> >>> diff --git a/net/core/filter.c b/net/core/filter.c >>> index 5912c738a7b2..3767470cab6c 100644 >>> --- a/net/core/filter.c >>> +++ b/net/core/filter.c >>> @@ -2566,13 +2566,19 @@ int xdp_do_generic_redirect(struct net_device *dev, struct sk_buff *skb, >>> struct bpf_prog *xdp_prog) >>> { >>> struct redirect_info *ri = this_cpu_ptr(&redirect_info); >>> + struct bpf_map *map = ri->map; >>> u32 index = ri->ifindex; >>> struct net_device *fwd; >>> unsigned int len; >>> int err = 0; >>> >>> - fwd = dev_get_by_index_rcu(dev_net(dev), index); >>> ri->ifindex = 0; >>> + ri->map = NULL; >>> + >>> + if (map) >>> + fwd = __dev_map_lookup_elem(map, index); >>> + else >>> + fwd = dev_get_by_index_rcu(dev_net(dev), index); >>> if (unlikely(!fwd)) { >>> err = -EINVAL; >>> goto err; >>> @@ -2590,10 +2596,12 @@ int xdp_do_generic_redirect(struct net_device *dev, struct sk_buff *skb, >>> } >>> >>> skb->dev = fwd; >> >> Looks much better above, thanks! >> >>> - _trace_xdp_redirect(dev, xdp_prog, index); >>> + map ? _trace_xdp_redirect_map(dev, xdp_prog, fwd, map, index) >>> + : _trace_xdp_redirect(dev, xdp_prog, index); >> >> Could we rather make this in a way such that when the two >> tracepoints are disabled and thus patched out, that we can >> also omit the extra conditional which has no purpose then? > > First of all I don't think it make much of a difference, I measured the > impact of the full patch to "cost" 1.62 nanosec (which is arguably > below the accuracy level of the system under test) > > Secondly, I plan to optimize the map case for generic XDP later, where > I would naturally split this into two functions (as V1, and as > native-XDP), thus this extra conditional would go away. As I've shown > offlist (to you, John and Andy) I demonstrated a 24% speedup via a > xmit_more hack for generic XDP. Okay, that would be nice indeed to have xmit_more support for generic XDP as well. If this is going to be split off anyway later on as in xdp_do_redirect() case, then: Acked-by: Daniel Borkmann