Re: [PATCH net-next v6 01/18] net: Declare MSG_SPLICE_PAGES internal sendmsg() flag

[Al Viro]

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@xxxxxxxxxxxxxxxxxx> 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...