[PATCH 4/4] wayland-server: Abort if a read from a client gives 0 length

[Karsten Otto]

Am 29.09.2014 um 06:31 schrieb Jason Ekstrand <jason at jlekstrand.net>:

> 
> On Sep 28, 2014 11:49 AM, "Karsten Otto" <karsten.otto at posteo.de> wrote:
> >
> > From: Philip Withnall <philip at tecnocode.co.uk>
> >
> > This happens if the socket has been gracefully closed.
> >
> > [KAO: It prevents a potential infinite loop when using a different
> > event handling mechanism than epoll, if said mechanism cannot
> > distinguish EOF from regular read (e.g. select).]
> > ---
> >  src/wayland-server.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/src/wayland-server.c b/src/wayland-server.c
> > index 674aeca..85741cb 100644
> > --- a/src/wayland-server.c
> > +++ b/src/wayland-server.c
> > @@ -260,7 +260,7 @@ wl_client_connection_data(int fd, uint32_t mask, void *data)
> >         len = 0;
> >         if (mask & WL_EVENT_READABLE) {
> >                 len = wl_connection_read(connection);
> > -               if (len < 0 && errno != EAGAIN) {
> > +               if (len == 0 || (len < 0 && errno != EAGAIN)) {
> >                         wl_client_destroy(client);
> >                         return 1;
> 
> It seems to me as if we should push this up the pipe to wl_connection_read so we fix it server-side too.
> 
What do you mean? Calling wl_client_destroy within wl_client_read? Or making sure the connection is properly disposed of in both client and server code?

Regarding the first, you would have to pass the wl_client reference to the read function, which would mix API layers unnecessarily. wl_client_read is basically just a convenient wrapper around recvmsg, so it should expose the same result semantics of >0 (OK), == 0 (EOF), and <0 (error), as it already does. It is up to the caller to handle the cases, if only to provide different log messages for error and EOF.

Regarding the second, wl_connection_read is part of the wayland private/internal API, and only used in two places: wayland-client.c, which already handles EOF in an appropriate manner, and wayland-server.c, where the proposed patch handles the missing case as well. If anybody else needs to use wl_connection_read within the wayland libraries in the future, they are hopefully aware of the recv result semantics. If necessary, maybe add some documentation to wayland-private.h. 

> >                 }
> > --
> > 1.9.1
> >
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