Re: [PATCH] io: prevent unbounded read of websocket data from client

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Sep 29, 2026 at 12:09:35AM +0400, Marc-André Lureau wrote:
> On Mon, Sep 28, 2026 at 5:09 PM Daniel P. Berrangé <berrange@redhat.com> wrote:
> >
> > The QIOChannelWebsock class wraps an underlying QIOChannel instance,
> > providing a websocket server handshake and packet encoding/decoding.
> >
> > When a watch is added to QIOChannelWebsock, this in turn creates a watch
> > on the underlying QIOChannel that is always monitoring G_IO_IN, as long
> > as the 'encinput' buffer has space.
> >
> > When this watch fires, it reads data off the wire into 'encinput' and
> > then decodes as much of 'encinput' as possible into the 'rawinput'
> > buffer.
> >
> > The qio_channel_websock_set_watch method checks to see that 'encinput'
> > does not exceed a max limit, but fails to check that 'rawinput' size.
> > Since any data read into 'encinput', can usually be immediately decoded
> > into 'rawinput', the 'encinput' size check is largely a no-op, and so
> > 'rawinput' will grow without bound.
> >
> > This is readily seen with the chardev socket backend if enabling
> > websockets, connecting a client that sends data, while not running any
> > guest OS to consume data from the chardev via a virtual serial port.
> >
> > The qio_channel_websock_read_wire() method will also unconditionally
> > read more data into 'encinput' if it has less than 4k present, which
> > is then decoded into 'rawinput'.
> >
> > IOW, if qio_channel_websock_read_wire() is triggered for lots of small
> > reads, it will be reading and decoding more data to 'rawinput' than is
> > consumed. Skip reading more data if 'rawinput' is already at its max
> > size.
> >
> > Reported-by: Aisle Research
> > Fixes: CVE-2026-101291
> > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> 
> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> 
> not sure if it's worth to add:
> Fixes: 2d1d0e70cf3e ("io: add QIOChannelWebsock class")

Doesn't hurt, so might as well.

With regards,
Daniel
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