From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [bpf-next PATCH 4/7] net: do_tcp_sendpages flag to avoid SKBTX_SHARED_FRAG Date: Fri, 12 Jan 2018 12:46:35 -0800 Message-ID: <1515789995.131759.50.camel@gmail.com> References: <20180112175029.21531.54693.stgit@john-Precision-Tower-5810> <20180112181055.21531.95322.stgit@john-Precision-Tower-5810> <1515787845.131759.46.camel@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, kafai@fb.com To: John Fastabend , borkmann@iogearbox.net, ast@kernel.org Return-path: Received: from mail-pf0-f193.google.com ([209.85.192.193]:34945 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964844AbeALUqh (ORCPT ); Fri, 12 Jan 2018 15:46:37 -0500 Received: by mail-pf0-f193.google.com with SMTP id t12so5244796pfg.2 for ; Fri, 12 Jan 2018 12:46:37 -0800 (PST) In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Fri, 2018-01-12 at 12:26 -0800, John Fastabend wrote: > On 01/12/2018 12:10 PM, Eric Dumazet wrote: > > On Fri, 2018-01-12 at 10:10 -0800, John Fastabend wrote: > > > When calling do_tcp_sendpages() from in kernel and we know the data > > > has no references from user side we can omit SKBTX_SHARED_FRAG flag. > > > This patch adds an internal flag, NO_SKBTX_SHARED_FRAG that can be used > > > to omit setting SKBTX_SHARED_FRAG. > > > > > > Signed-off-by: John Fastabend > > > --- > > > include/linux/socket.h | 1 + > > > net/ipv4/tcp.c | 4 +++- > > > 2 files changed, 4 insertions(+), 1 deletion(-) > > > > > > diff --git a/include/linux/socket.h b/include/linux/socket.h > > > index 9286a5a..add9360 100644 > > > --- a/include/linux/socket.h > > > +++ b/include/linux/socket.h > > > @@ -287,6 +287,7 @@ struct ucred { > > > #define MSG_SENDPAGE_NOTLAST 0x20000 /* sendpage() internal : not the last page */ > > > #define MSG_BATCH 0x40000 /* sendmmsg(): more messages coming */ > > > #define MSG_EOF MSG_FIN > > > +#define MSG_NO_SHARED_FRAGS 0x80000 /* sendpage() internal : page frags are not shared */ > > > > > > #define MSG_ZEROCOPY 0x4000000 /* Use user data in kernel path */ > > > #define MSG_FASTOPEN 0x20000000 /* Send data in TCP SYN */ > > > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c > > > index 7ac583a..56c6f49 100644 > > > --- a/net/ipv4/tcp.c > > > +++ b/net/ipv4/tcp.c > > > @@ -995,7 +995,9 @@ ssize_t do_tcp_sendpages(struct sock *sk, struct page *page, int offset, > > > get_page(page); > > > skb_fill_page_desc(skb, i, page, offset, copy); > > > } > > > - skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG; > > > + > > > + if (!(flags & MSG_NO_SHARED_FRAGS)) > > > + skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG; > > > > > > skb->len += copy; > > > skb->data_len += copy; > > > > What would prevent user space from using this flag ? > > > > Nothing in the current patches. So user could set this, change the data, > and then presumably get incorrect checksums with bad timing. Seems like > this should be blocked so we don't allow users to try and send bad csums. Are you sure user can set it ? How would this happen ? It would be nice to check (sorry I was lazy/busy and did not check before asking) > How about masking the flags coming from userland? Alternatively could add > a bool to do_tcp_sendpages(). >