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Miller'" , "'Jakub Kicinski'" , "'Network Development'" , "'linux-kernel'" In-Reply-To: Subject: RE: [PATCH bpf] bpf: check for data_len before upgrading mss when 6 to 4 Date: Thu, 6 May 2021 11:27:43 +0900 Message-ID: <02c801d7421f$65287a90$2f796fb0$@samsung.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Outlook 16.0 Content-Language: ko Thread-Index: AQKypHYW3xad5/j2XvChPebQmKG2owG+YoocAqFpyMsBZavlXQIxNaIYqN8+O7A= X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFtrFJsWRmVeSWpSXmKPExsWy7bCmqa5iyOQEg9NdEhbff89mtvjy8za7 xecjx9ksFi/8xmwx53wLi0XTjhVMFi8+PGG0eL6vl8niwrY+VovLu+awWRxbIGbx8/AZZovF PzcAVSyZwejA57Fl5U0mj4nN79g9ds66y+7RdeMSs8emVZ1sHp83yQWwReXYZKQmpqQWKaTm JeenZOal2yp5B8c7x5uaGRjqGlpamCsp5CXmptoqufgE6Lpl5gBdq6RQlphTChQKSCwuVtK3 synKLy1JVcjILy6xVUotSMkpMDQs0CtOzC0uzUvXS87PtTI0MDAyBapMyMm4cr2PuWCBUsW5 HSsYGxgnSnYxcnJICJhIPF47k72LkYtDSGAHo8SsGQvYQBJCAp8YJea9d4VIfGaUODtpOjtM R+u0LYwQiV2MEn/XTWCBcF4wSmxd0QpWxSagJfFmVjsriC0iYCXxf/YJsDizwDwWibZTIiA2 p0CgxO5ZP5hBbGGBYImnk5qYuhg5OFgEVCQ2XHUBCfMKWEp0b97MDmELSpyc+YQFYoy8xPa3 c5ghDlKQ+Pl0GStEXERidmcbM8RaP4nHjz5CHX2BQ+Lb2giQ8RICLhIHlrBAhIUlXh3fAlUi JfGyv40doqReorU7BuQrCYEeRokr+55A1RtLzHrWzghSwyygKbF+lz5EubLEkVtQh/FJdBz+ CzWFV6KjTQjCVJKY+CUeYoaExIuTk1kmMCrNQvLVLCRfzULyySyEVQsYWVYxiqUWFOempxYb FRghx/MmRnAi1nLbwTjl7Qe9Q4xMHIyHGCU4mJVEeAvW9icI8aYkVlalFuXHF5XmpBYfYjQF BvNEZinR5HxgLsgriTc0NTIzM7A0tTA1M7JQEuf9mVqXICSQnliSmp2aWpBaBNPHxMEp1cBk t3RFp/ouzwIxxXMHhPPuKmzuYvXbpxp7miMhzG/WWdesJ7+4jl/U1ZGYVGAwx9H2rfPJEM3X jxvYe2xEHuczS7UzTH/RlaoaqXvIdpHM3x0H3zLOSb853TRfgDH19+MPEX4+OXJvZs99u1Ty 2NQdAapvWp/dm3nUyJrTdkP61WiZZy/Ktk0Q40/2c+N4sjV+9pIdZetuswh6/q1Ouy9wIPbk JsOZb+WtZV6s9Z0acnjpdJsnW040NbZdsVphrr/76sNCw/dKQQXv/nVLzfs50XahQ/+2k99/ rF7A+/dfoj/z+xvLryakHv4VFuOu1lYqmcgpPUVGxlhkw94e3wm83BW/bc9+lV115MYeGdFa JZbijERDLeai4kQA79dojU0EAAA= X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFlrBIsWRmVeSWpSXmKPExsWy7bCSnK5CyOQEg/fqFt9/z2a2+PLzNrvF 5yPH2SwWL/zGbDHnfAuLRdOOFUwWLz48YbR4vq+XyeLCtj5Wi8u75rBZHFsgZvHz8Blmi8U/ NwBVLJnB6MDnsWXlTSaPic3v2D12zrrL7tF14xKzx6ZVnWwenzfJBbBFcdmkpOZklqUW6dsl cGVcud7HXLBAqeLcjhWMDYwTJbsYOTkkBEwkWqdtYQSxhQR2MErs73LoYuQAiktI7NrsClEi LHG/5QhrFyMXUMkzoJLVm1lAEmwCWhJvZrWzgtgiAlYS/2efYAcpYhZYwSJxoOM9O0THXiaJ K1c/g1VxCgRK7J71gxnEFgay+//dYgTZxiKgIrHhqgtImFfAUqJ782Z2CFtQ4uTMJ2DLmAW0 JXoftjJC2PIS29/OYYa4TkHi59NlrBBxEYnZnW3MEAf5STx+9JF9AqPwLCSjZiEZNQvJqFlI 2hcwsqxilEwtKM5Nzy02LDDKSy3XK07MLS7NS9dLzs/dxAiOTC2tHYx7Vn3QO8TIxMF4iFGC g1lJhLdgbX+CEG9KYmVValF+fFFpTmrxIUZpDhYlcd4LXSfjhQTSE0tSs1NTC1KLYLJMHJxS DUzunKIp6Y2Mia6LOrPfOtxWNebcetf1TuWCtGqjiwzTps7cV+mb5fpkY3UEK+uU7mlqbb8/ bluz4+SvfVl+PK+vvzG9GzT/vOTfDdYO7FeNfte1J+3WUNv2VcU+1D1tk5z0pFuO1Yxf120z a35h91cvy/6WEuf9JuuyadzTPV9POijOr/Jcx2/17Zc1FoXXtva93GzvvmN78pF4rxuiilPv iGg/Ob7EKdHtSnnJjFuVwkrqBzbdUWgQ7mmdb8HGLxJ1ri5x85pp/OdCrrClbpQMjm248mid 2bYU84Wtk9lYJjPyas24EdPJ9mBuot35y1PNeAJv1c7kPur7bOrLlQfmLvxRKhce/vClbEed QpMSS3FGoqEWc1FxIgAgod7UOwMAAA== X-CMS-MailID: 20210506022744epcas2p1207466493a0e0da9d4ee6c14e1182242 X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" X-Sendblock-Type: AUTO_CONFIDENTIAL CMS-TYPE: 102P DLP-Filter: Pass X-CFilter-Loop: Reflected X-CMS-RootMailID: 20210429102143epcas2p4c8747c09a9de28f003c20389c050394a References: <1619690903-1138-1-git-send-email-dseok.yi@samsung.com> <8c2ea41a-3fc5-d560-16e5-bf706949d857@iogearbox.net> <02bf01d74211$0ff4aed0$2fde0c70$@samsung.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 05, 2021 at 09:45:37PM -0400, Willem de Bruijn wrote: > On Wed, May 5, 2021 at 8:45 PM Dongseok Yi wrote: > > > > On Wed, May 05, 2021 at 10:55:10PM +0200, Daniel Borkmann wrote: > > > On 4/29/21 12:08 PM, Dongseok Yi wrote: > > > > tcp_gso_segment check for the size of GROed payload if it is bigger > > > > than the mss. bpf_skb_proto_6_to_4 increases mss, but the mss can be > > > > bigger than the size of GROed payload unexpectedly if data_len is not > > > > big enough. > > > > > > > > Assume that skb gso_size = 1372 and data_len = 8. bpf_skb_proto_6_to_4 > > Is this a typo and is this intended to read skb->data_len = 1380? This is not a typo. I intended skb->data_len = 8. > > The issue is that payload length (1380) is greater than mss with ipv6 > (1372), but less than mss with ipv4 (1392). > > I don't understand data_len = 8 or why the patch compares > skb->data_len to len_diff (20). skb_gro_receive(): unsigned int len = skb_gro_len(skb); [...] done: NAPI_GRO_CB(p)->count++; p->data_len += len; head_skb's data_len is the sum of skb_gro_len for each skb of the frags. data_len could be 8 if server sent a small size packet and it is GROed to head_skb. Please let me know if I am missing something. > > One simple solution if this packet no longer needs to be segmented > might be to reset the gso_type completely. I am not sure gso_type can be cleared even when GSO is needed. > > In general, I would advocate using BPF_F_ADJ_ROOM_FIXED_GSO. When > converting from IPv6 to IPv4, fixed gso will end up building packets > that are slightly below the MTU. That opportunity cost is negligible > (especially with TSO). Unfortunately, I see that that flag is > available for bpf_skb_adjust_room but not for bpf_skb_proto_6_to_4. > > > > > > would increse the gso_size to 1392. tcp_gso_segment will get an error > > > > with 1380 <= 1392. > > > > > > > > Check for the size of GROed payload if it is really bigger than target > > > > mss when increase mss. > > > > > > > > Fixes: 6578171a7ff0 (bpf: add bpf_skb_change_proto helper) > > > > Signed-off-by: Dongseok Yi > > > > --- > > > > net/core/filter.c | 4 +++- > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/net/core/filter.c b/net/core/filter.c > > > > index 9323d34..3f79e3c 100644 > > > > --- a/net/core/filter.c > > > > +++ b/net/core/filter.c > > > > @@ -3308,7 +3308,9 @@ static int bpf_skb_proto_6_to_4(struct sk_buff *skb) > > > > } > > > > > > > > /* Due to IPv4 header, MSS can be upgraded. */ > > > > - skb_increase_gso_size(shinfo, len_diff); > > > > + if (skb->data_len > len_diff) > > > > > > Could you elaborate some more on what this has to do with data_len specifically > > > here? I'm not sure I follow exactly your above commit description. Are you saying > > > that you're hitting in tcp_gso_segment(): > > > > > > [...] > > > mss = skb_shinfo(skb)->gso_size; > > > if (unlikely(skb->len <= mss)) > > > goto out; > > > [...] > > > > Yes, right > > > > > > > > Please provide more context on the bug, thanks! > > > > tcp_gso_segment(): > > [...] > > __skb_pull(skb, thlen); > > > > mss = skb_shinfo(skb)->gso_size; > > if (unlikely(skb->len <= mss)) > > [...] > > > > skb->len will have total GROed TCP payload size after __skb_pull. > > skb->len <= mss will not be happened in a normal GROed situation. But > > bpf_skb_proto_6_to_4 would upgrade MSS by increasing gso_size, it can > > hit an error condition. > > > > We should ensure the following condition. > > total GROed TCP payload > the original mss + (IPv6 size - IPv4 size) > > > > Due to > > total GROed TCP payload = the original mss + skb->data_len > > IPv6 size - IPv4 size = len_diff > > > > Finally, we can get the condition. > > skb->data_len > len_diff > > > > > > > > > + skb_increase_gso_size(shinfo, len_diff); > > > > + > > > > /* Header must be checked, and gso_segs recomputed. */ > > > > shinfo->gso_type |= SKB_GSO_DODGY; > > > > shinfo->gso_segs = 0; > > > > > > > >