[FFmpeg-devel] [PATCH v6] avdevice/xcbgrab: check return values of xcb query functions

[Andriy Gelman]

On Wed, 05. Aug 14:37, Moritz Barsnick wrote:
> On Mon, Jul 20, 2020 at 09:18:55 +0200, Alexander Strasser wrote:
> > On 2020-07-19 19:47 -0400, Andriy Gelman wrote:
> > > > > This check seems dead code. Looking at xcb sources, cursor is just an offset in
> > > > > memory from ci so I don't think it can be null here.
> 
> > > But anyway, this part of the patch doesn't really have anything to do with
> > > ticket #7312, and should be in a separate patch.
> >
> > Yes, it's definitely something that was changed in this patch
> > at all. So it's better not to touch it in this patch.
> 
> Okay, so I "fixed" dead code. You guys can remove the dead code
> yourselves then, if you like. ;-)
> 
> New patch for the original issue attached, not touching the dead code.
> 
> Thanks,
> Moritz

> From e44b7f03354add2272a2739e04aafb38b7ce027f Mon Sep 17 00:00:00 2001
> From: Moritz Barsnick <barsnick at gmx.net>
> Date: Wed, 5 Aug 2020 14:06:53 +0200
> Subject: [PATCH] avdevice/xcbgrab: check return values of xcb query functions
> 
> Fixes #7312, segmentation fault on close of X11 server
> 
> xcb_query_pointer_reply() and xcb_get_geometry_reply() can return NULL
> if e.g. the X server closes or the connection is lost. This needs to
> be checked in order to cleanly exit, because the returned pointers are
> dereferenced later.
> 
> Signed-off-by: Moritz Barsnick <barsnick at gmx.net>
> ---
>  libavdevice/xcbgrab.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/libavdevice/xcbgrab.c b/libavdevice/xcbgrab.c
> index 6f6b2dbf15..8ef2a30d02 100644
> --- a/libavdevice/xcbgrab.c
> +++ b/libavdevice/xcbgrab.c
> @@ -425,7 +425,16 @@ static int xcbgrab_read_packet(AVFormatContext *s, AVPacket *pkt)
>          pc  = xcb_query_pointer(c->conn, c->screen->root);
>          gc  = xcb_get_geometry(c->conn, c->screen->root);
>          p   = xcb_query_pointer_reply(c->conn, pc, NULL);
> +        if (!p) {
> +            av_log(s, AV_LOG_ERROR, "Failed to query xcb pointer\n");
> +            return AVERROR_EXTERNAL;
> +        }
>          geo = xcb_get_geometry_reply(c->conn, gc, NULL);
> +        if (!geo) {
> +            av_log(s, AV_LOG_ERROR, "Failed to get xcb geometry\n");
> +            free(p);
> +            return AVERROR_EXTERNAL;
> +        }
>      }
> 
>      if (c->follow_mouse && p->same_screen)
> --
> 2.26.2
> 

lgtm

Thanks,
-- 
Andriy