Subject: Re: [PATCHv3 net-next 4/4] sctp: implement sender-side procedures for Add Incoming/Outgoing Streams Request Parameter

From: Marcelo Ricardo Leitner <[email-masked]>
Date: Mon, 23 Jan 2017 14:02:34 -0200

On Mon, Jan 23, 2017 at 09:53:47AM -0500, Neil Horman wrote:
> On Mon, Jan 23, 2017 at 11:25:56AM +0000, David Laight wrote:
> > From: Xin Long
> > > Sent: 19 January 2017 17:19
> > > This patch is to implement Sender-Side Procedures for the Add
> > > Outgoing and Incoming Streams Request Parameter described in
> > > rfc6525 section 5.1.5-5.1.6.
> > > 
> > > It is also to add sockopt SCTP_ADD_STREAMS in rfc6525 section
> > > 6.3.4 for users.
> > ...
> > > +	out = params->sas_outstrms;
> > > +	in  = params->sas_instrms;
> > > +
> > > +	if (!out && !in)
> > > +		goto out;
> > > +
> > > +	if (out) {
> > > +		__u16 nums = stream->outcnt + out;
> > 
> > Make nums 'unsigned int', the code will be smaller and you can
> > use the value for the overflow check.
> > 
> > > +		/* Check for overflow, can't use nums here */
> > > +		if (stream->outcnt + out > SCTP_MAX_STREAM)
> > > +			goto out;
> > > +
> > > +		/* Use ksize to check if stream array really needs to realloc */
> > > +		if (ksize(stream->out) / sizeof(*stream->out) < nums) {
> > > +			struct sctp_stream_out *streamout;
> > > +
> > > +			streamout = kcalloc(nums, sizeof(*streamout),
> > > +					    GFP_KERNEL);
> > > +			if (!streamout) {
> > > +				retval = -ENOMEM;
> > > +				goto out;
> > > +			}
> > > +
> > > +			memcpy(streamout, stream->out,
> > > +			       sizeof(*streamout) * stream->outcnt);
> > > +
> > > +			kfree(stream->out);
> > > +			stream->out = streamout;
> > > +		}
> > 
> > Does kcalloc() zero the entire area, or just the length you ask for?
> > If the latter you need to zero the rest here.
> Better still, just use krealloc.  You still need to zero out any space beyond
> the old length, but it will make the code shorter, and avoid the need for
> additional temporary variables.

Seems if we pass gfp | __GFP_ZERO to krealloc it will end up zeroing the
slab for us before doing the memcpy.
I didn't follow all paths but in slab_alloc_node it will end up calling:
        if (unlikely(gfpflags & __GFP_ZERO) && object)
                memset(object, 0, s->object_size);
So I would expect that other paths also do it.

  Marcelo

> 
> Neil
> 
> > ...
> > 
> > 	David
> > 
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