[Spice-devel] [PATCH spice-server] cursor-channel: Remove obsolete size check

[Frediano Ziglio]

ping

> 
> > 
> > Hi,
> > 
> > On Mon, May 22, 2017 at 11:41:02AM +0100, Frediano Ziglio wrote:
> > > In the past CursorItem structure was stored in
> > > RedCursorCmd::device_data field so the check was there to check if the
> > > structure fit into that field.
> > > Since 2ba69f9f8819daaa3d166c4c1c7e03b121b88a95
> > 
> > A lit bit hard to follow, this one
> > 
> 
> Yes, the mentioned patch is quite big and the topic is not much related
> to this. However you can see that "device_data" access was removed.
> 
> > > ("libspice: add surface 0 support") the structure is no more stored in
> > > the field so there's no reason for this check causing only confusion.
> > >
> > > Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
> > > ---
> > >  server/cursor-channel.c | 2 --
> > >  1 file changed, 2 deletions(-)
> > >
> > > diff --git a/server/cursor-channel.c b/server/cursor-channel.c
> > > index 6aea64a..a876113 100644
> > > --- a/server/cursor-channel.c
> > > +++ b/server/cursor-channel.c
> > > @@ -34,8 +34,6 @@ typedef struct CursorItem {
> > >      RedCursorCmd *red_cursor;
> > >  } CursorItem;
> > >
> > > -G_STATIC_ASSERT(sizeof(CursorItem) <= QXL_CURSUR_DEVICE_DATA_SIZE);
> > > -
> > 
> > I don't see any other use for QXL_CURSUR_DEVICE_DATA_SIZE in my local
> > workspace besides:
> > 
> >   spice-protocol/spice/qxl_dev.h:335:
> >   #define QXL_CURSUR_DEVICE_DATA_SIZE 128
> >   spice-protocol/spice/qxl_dev.h:352:
> >   uint8_t device_data[QXL_CURSUR_DEVICE_DATA_SIZE]; //todo: dynamic size
> >   from
> >   rom
> > 
> > Is that useless now?
> > 
> 
> Maybe but is not so easy to remove. Now, did some grep too and basically
> nobody uses device_data field. Is not surprising as was used to store
> spice-server data in qxl card memory... once spice-server usage was
> gone the fields stopped to be used.
> 
> However this now is an ABI and the size of QXLCursorCmd is part of
> the ABI. Although this is the last field and QXLCursorCmd is not
> included in any array/structures (but just pointed from the cursor
> ring) this can cause problems. Let say for instance that the field is
> removed. The QXL drivers will allocate less bytes and pass less bytes.
> Now if the spice-server you are using is using the old length it will
> check for memory bounds using the old (bigger) size. If the cursor
> commands was allocated at the end of QXL memory region (quite unlikely
> but not impossible) the red-parse-qxl.c code will detect an error and
> discard the command. Not sure if this is the only issue of removing
> the field but I think that this change is not strongly related to
> this one and should be addresses in a follow up.
> 
> > (hmm, checking qxl-wddm-dod)
> > [0] https://gitlab.com/spice/qxl-wddm-dod
> > 
> > Okay, here is also not used and header is actually duplicated (shouldn't
> > we use the header from spice-protocol here? see:
> > 
> >   $ qxl-wddm-dod (master 1a81d6d3) $ grepi "qxl_dev" *
> >   qxldod/include/qxl_dev.h:32:#ifndef _H_QXL_DEV
> >   qxldod/include/qxl_dev.h:33:#define _H_QXL_DEV
> >   qxldod/include/qxl_dev.h:65:#define QXL_DEVICE_ID_STABLE 0x0100
> >   qxldod/include/qxl_dev.h:74:#define QXL_DEVICE_ID_DEVEL 0x01ff
> >   qxldod/include/qxl_dev.h:808:#endif /* _H_QXL_DEV */
> >   qxldod/QxlDod.h:13:#include "qxl_dev.h"
> > 
> > Anyway, patch looks fine but we might want to do some follow ups.
> > 
> 
> Yes, surely.
> 
> > >  struct CursorChannel
> > >  {
> > >      CommonGraphicsChannel parent;
> 
> Frediano