linux-kernel - Re: [RFC PATCH 03/28] tcp: Support MSG_SPLICE

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <6419bda5a2b4d_59e87208ca@willemb.c.googlers.com.notmuch>
Date:   Tue, 21 Mar 2023 10:22:29 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     David Howells <dhowells@...hat.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     dhowells@...hat.com, Matthew Wilcox <willy@...radead.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jeff Layton <jlayton@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        netdev@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH 03/28] tcp: Support MSG_SPLICE_PAGES

David Howells wrote:
> Willem de Bruijn <willemdebruijn.kernel@...il.com> wrote:
> 
> > David Howells wrote:
> > > Willem de Bruijn <willemdebruijn.kernel@...il.com> wrote:
> > > 
> > > > The commit message mentions MSG_SPLICE_PAGES as an internal flag.
> > > > 
> > > > It can be passed from userspace. The code anticipates that and checks
> > > > preconditions.
> > > 
> > > Should I add a separate field in the in-kernel msghdr struct for such internal
> > > flags?  That would also avoid putting an internal flag in the same space as
> > > the uapi flags.
> > 
> > That would work, if no cost to common paths that don't need it.
> 
> Actually, it might be tricky.  __ip_append_data() doesn't take a msghdr struct
> pointer per se.  The "void *from" argument *might* point to one - but it
> depends on seeing a MSG_SPLICE_PAGES or MSG_ZEROCOPY flag, otherwise we don't
> know.
> 
> Possibly this changes if sendpage goes away.

Is it sufficient to mask out this bit in tcp_sendmsg_locked and
udp_sendmsg if passed from userspace (and should be ignored), and pass
it through flags to callees like ip_append_data?
> 
> > A not very pretty alternative would be to add an an extra arg to each
> > sendmsg handler that is used only when called from sendpage.
> > 
> > There are a few other internal MSG_.. flags, such as
> > MSG_SENDPAGE_NOPOLICY. Those are all limited to sendpage, and ignored
> > in sendmsg, I think. Which would explain why it was clearly safe to
> > add them.
> 
> Should those be moved across to the internal flags with MSG_SPLICE_PAGES?

I would not include that in this patch series.