netdev - Re: [PATCHv2 net] sctp: check and update stream->out_curr when allocating stream

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Date:   Thu, 29 Nov 2018 23:31:04 +0900
From:   Xin Long <lucien.xin@...il.com>
To:     Neil Horman <nhorman@...driver.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        davem <davem@...emloft.net>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: Re: [PATCHv2 net] sctp: check and update stream->out_curr when
 allocating stream_out

On Thu, Nov 29, 2018 at 9:50 PM Neil Horman <nhorman@...driver.com> wrote:
>
> On Thu, Nov 29, 2018 at 02:42:56PM +0800, Xin Long wrote:
> > Now when using stream reconfig to add out streams, stream->out
> > will get re-allocated, and all old streams' information will
> > be copied to the new ones and the old ones will be freed.
> >
> > So without stream->out_curr updated, next time when trying to
> > send from stream->out_curr stream, a panic would be caused.
> >
> > This patch is to check and update stream->out_curr when
> > allocating stream_out.
> >
> > v1->v2:
> >   - define fa_index() to get elem index from stream->out_curr.
> >
> > Fixes: 5bbbbe32a431 ("sctp: introduce stream scheduler foundations")
> > Reported-by: Ying Xu <yinxu@...hat.com>
> > Reported-by: syzbot+e33a3a138267ca119c7d@...kaller.appspotmail.com
> > Signed-off-by: Xin Long <lucien.xin@...il.com>
> > ---
> >  net/sctp/stream.c | 20 ++++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> >
> > diff --git a/net/sctp/stream.c b/net/sctp/stream.c
> > index 3892e76..30e7809 100644
> > --- a/net/sctp/stream.c
> > +++ b/net/sctp/stream.c
> > @@ -84,6 +84,19 @@ static void fa_zero(struct flex_array *fa, size_t index, size_t count)
> >       }
> >  }
> >
> > +static size_t fa_index(struct flex_array *fa, void *elem, size_t count)
> > +{
> > +     size_t index = 0;
> > +
> > +     while (count--) {
> > +             if (elem == flex_array_get(fa, index))
> > +                     break;
> > +             index++;
> > +     }
> > +
> > +     return index;
> > +}
> > +
> >  /* Migrates chunks from stream queues to new stream queues if needed,
> >   * but not across associations. Also, removes those chunks to streams
> >   * higher than the new max.
> > @@ -147,6 +160,13 @@ static int sctp_stream_alloc_out(struct sctp_stream *stream, __u16 outcnt,
> >
> >       if (stream->out) {
> >               fa_copy(out, stream->out, 0, min(outcnt, stream->outcnt));
> > +             if (stream->out_curr) {
> > +                     size_t index = fa_index(stream->out, stream->out_curr,
> > +                                             stream->outcnt);
> > +
> > +                     BUG_ON(index == stream->outcnt);
> > +                     stream->out_curr = flex_array_get(out, index);
> > +             }
> >               fa_free(stream->out);
> >       }
> >
> > --
> > 2.1.0
> >
> >
>
> I'm having a hard time understanding why, as I noted earlier, you don't just
> write a function in the flex_array code that can resize the number of elements
> in your array.  If you do that, you can avoid both all the copying, and the need
> to lookup the in-use pointer again
didn't want to touch the flex_array code, but you're right,
it would avoid both the copying and the lookup. I will
have a try tomorrow in flex_array.c, thanks.

>
> Neil
>