Re: [PATCH 2/3 for 9.0] Revert "chardev/char-socket: Fix TLS io channels sending too much data to the backend"

[Daniel P . Berrangé]

On Mon, Mar 18, 2024 at 11:09:23PM +0400, Marc-André Lureau wrote:
> Hi
> 
> On Mon, Mar 18, 2024 at 10:23 PM Daniel P. Berrangé <berrange@redhat.com> 
> wrote:
> >
> > This commit results in unexpected termination of the TLS connection.
> > When 'fd_can_read' returns 0, the code goes on to pass a zero length
> > buffer to qio_channel_read. The TLS impl calls into gnutls_recv()
> > with this zero length buffer, at which point GNUTLS returns an error
> > GNUTLS_E_INVALID_REQUEST. This is treated as fatal by QEMU's TLS code
> > resulting in the connection being torn down by the chardev.
> >
> > Simply skipping the qio_channel_read when the buffer length is zero
> > is also not satisfactory, as it results in a high CPU burn busy loop
> > massively slowing QEMU's functionality.
> >
> > The proper solution is to avoid tcp_chr_read being called at all
> > unless the frontend is able to accept more data. This will be done
> > in a followup commit.
> >
> > This reverts commit 1907f4d149c3589ade641423c6a33fd7598fa4d3.
> 
> Actually 462945cd22d2bcd233401ed3aa167d83a8e35b05 upstream.

Opps, yes, will fix this before I send a pull.

> 
> >
> > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> > ---
> >  chardev/char-socket.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/chardev/char-socket.c b/chardev/char-socket.c
> > index 2c4dffc0e6..812d7aa38a 100644
> > --- a/chardev/char-socket.c
> > +++ b/chardev/char-socket.c
> > @@ -496,9 +496,9 @@ static gboolean tcp_chr_read(QIOChannel *chan, 
> > GIOCondition cond, void *opaque)
> >          s->max_size <= 0) {
> >          return TRUE;
> >      }
> > -    len = tcp_chr_read_poll(opaque);
> > -    if (len > sizeof(buf)) {
> > -        len = sizeof(buf);
> > +    len = sizeof(buf);
> > +    if (len > s->max_size) {
> > +        len = s->max_size;
> >      }
> >      size = tcp_chr_recv(chr, (void *)buf, len);
> >      if (size == 0 || (size == -1 && errno != EAGAIN)) {
> > --
> > 2.43.0
> >
> 

With regards,
Daniel
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