linux-kernel - Re: [PATCH net-next v6 01/18] net: Declare MSG_SPLICE

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Date:   Thu, 13 Apr 2023 22:01:12 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     David Howells <dhowells@...hat.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        David Ahern <dsahern@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Christoph Hellwig <hch@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jeff Layton <jlayton@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        Chuck Lever III <chuck.lever@...cle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next v6 01/18] net: Declare MSG_SPLICE_PAGES internal
 sendmsg() flag

On Thu, Apr 13, 2023 at 09:49:18PM +0100, Al Viro wrote:
> On Thu, Apr 13, 2023 at 09:39:22PM +0100, David Howells wrote:
> > Al Viro <viro@...iv.linux.org.uk> wrote:
> > 
> > > Note that io_sendmsg_prep() handles both IORING_OP_SENDMSG and IORING_OP_SEND,
> > > so this pair of functions can hit the same request.  And sqe->msg_flags is
> > > not sanitized at all - it comes straight from user buffer.
> > 
> > Assuming ____sys_sendmsg() is fixed, I think it should be sufficient to make
> > io_send() and io_send_zc().  io_sendmsg() and io_sendmsg_zc() will go through
> > ____sys_sendmsg().
> 
> 	Sure; what I wanted to point out was that despite the name,
> io_sendmsg_prep() gets used not only with io_sendmsg().  io_sendmsg()
> does go through ____sys_sendmsg(), but io_send() goes straight to
> sock_sendmsg() and evades all your checks...

	Incidentally, having ____sendmsg and ___sendmsg in the same file
is more than slightly antisocial - compiler can sort it out, but there
are human readers as well.  We have
____sys_sendmsg
___sys_sendmsg
__sys_sendmsg
__sys_sendmmsg
next to each other.  Maze of twisty little identifiers, all alike...