Re: [PATCH net-next v4 03/11] splice, net: Use sendmsg(MSG_SPLICE_PAGES) rather than ->sendpage()

[Simon Horman]

On Mon, Jun 05, 2023 at 04:10:57PM +0100, David Howells wrote:
> Simon Horman <simon.horman@xxxxxxxxxxxx> wrote:
> 
> > I'm assuming the answer is that this cannot occur,
> > but I thought I should mention this anyway.
> > 
> > If the initial value of len is 0 (or less).
> > ...
> > > +	return spliced ?: ret;
> > 
> > Then ret will be used uninitialised here.
> 
> len shouldn't be <0 as it's size_t.

Yes, sorry for not noticing that.

> I don't think it should be possible to get there with len==0 - at least from
> userspace.  sys_splice() returns immediately and sys_sendfile() either splices
> to a pipe or goes via splice_direct_to_actor() will just drop straight out.
> But there are kernel users - nfsd for example - but I don't know if they would
> splice directly to a socket.
> 
> That said, it's probably worth preclearing ret just to be sure.

Thanks, I agree it's better to be safe than sorry.