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

[David Howells]

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.

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.

David