[Spice-devel] [spice-streaming-agent PATCH] handle_stream_error: add comment for inheriting struct

[Lukáš Hrázký]

On Wed, 2018-03-07 at 13:56 +0100, Christophe de Dinechin wrote:
> > On 7 Mar 2018, at 07:40, Frediano Ziglio <fziglio at redhat.com> wrote:
> > 
> > > 
> > > Introduced in 548577dc8adae1a558
> > > 
> > > Signed-off-by: Uri Lublin <uril at redhat.com>
> > > ---
> > > src/spice-streaming-agent.cpp | 5 +++++
> > > 1 file changed, 5 insertions(+)
> > > 
> > > diff --git a/src/spice-streaming-agent.cpp b/src/spice-streaming-agent.cpp
> > > index b39782c..e25d47a 100644
> > > --- a/src/spice-streaming-agent.cpp
> > > +++ b/src/spice-streaming-agent.cpp
> > > @@ -145,6 +145,11 @@ static void handle_stream_error(size_t len)
> > >                                  std::to_string(sizeof(StreamMsgNotifyError))
> > >                                  + ")");
> > >     }
> > > 
> > > +    // This struct inherits StreamMsgNotifyError. Its memory layout is:
> > > +    // offset 0: StreamMsgNotifyError.error_code (a uint32_t)
> > > +    // offset 4: StreamMsgNotifyError.msg and also msg.msg (a
> > > uint8_t[1024]).
> > > +    // Both StreamMsgNotifyError.msg and msg.msg point to the same
> > > +    // memory location (practically local msg overrides inherited msg).
> > >     struct : StreamMsgNotifyError {
> > >         uint8_t msg[1024];
> > >     } msg;
> > 
> > When I sent my suggestion I didn't wanted to clash with inherited field,
> > just didn't invented a new name.
> > Maybe would be easier and more clear to rename to msg_buffer or similar
> > to avoid the confusion?
> 
> Would fix the issue I pointed out. But as I mentioned there, gcc emkits a warning that we access the array out of bounds (msg has zero length). You can silence that using a temporary char * pointer.

Are you talking about the same thing as Frediano? IIUC:
- Frediano says rename msg.msg to msg.msg_buffer and use that

- You talk about out of bounds warning for StreamMsgNotifyError::msg
and casting it to a pointer to avoid that (so that we wouldn't need to
inherit the struct at all)

To sum it up, what changes are requested?

- Fix msg.msg in a TBD way.

- If the message is too long, read it out instead of throwing an
exception to prevent a DoS. (We can still get DoSed though if the
server sends a neverending message or whatever?)

- If the inherited struct stays, name it? (I have to say I liked the
unnamed struct in local scope as it limited it's usage exactly to the
one 'msg' variable...)

Cheers,
Lukas

> > 
> > Frediano
> > _______________________________________________
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> > Spice-devel at lists.freedesktop.org
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