[FFmpeg-devel] [PATCH v3] avdevice/xcbgrab: check return values of xcb query functions

[Moritz Barsnick]

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.

Furthermore, their return values need to be free()d, also in error
code paths.

Signed-off-by: Moritz Barsnick <barsn...@gmx.net>
---
To reproduce:
Terminal 1:
$ Xvfb :1 -nolisten tcp -screen 0 800x600x24
Terminal 2:
$ ffmpeg -f x11grab -i :1 -f null -
or rather
$ gdb -ex r --args ffmpeg_g -f x11grab -i :1 -f null -
Then terminate Xvfb while ffmpeg is running.

 libavdevice/xcbgrab.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/libavdevice/xcbgrab.c b/libavdevice/xcbgrab.c
index b7e689343e..3fb3c56285 100644
--- a/libavdevice/xcbgrab.c
+++ b/libavdevice/xcbgrab.c
@@ -326,8 +326,10 @@ static void xcbgrab_draw_mouse(AVFormatContext *s, 
AVPacket *pkt,
         return;

     cursor = xcb_xfixes_get_cursor_image_cursor_image(ci);
-    if (!cursor)
+    if (!cursor) {
+        free(ci);
         return;
+    }

     cx = ci->x - ci->xhot;
     cy = ci->y - ci->yhot;
@@ -404,7 +406,16 @@ 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(c, AV_LOG_ERROR, "Failed to query xcb pointer\n");
+            return AVERROR(EIO);
+        }
         geo = xcb_get_geometry_reply(c->conn, gc, NULL);
+        if (!geo) {
+            av_log(c, AV_LOG_ERROR, "Failed get xcb geometry\n");
+            free(p);
+            return AVERROR(EIO);
+        }
     }

     if (c->follow_mouse && p->same_screen)
@@ -537,6 +548,10 @@ static int create_stream(AVFormatContext *s)

     gc  = xcb_get_geometry(c->conn, c->screen->root);
     geo = xcb_get_geometry_reply(c->conn, gc, NULL);
+    if (!geo) {
+        av_log(c, AV_LOG_ERROR, "Failed to get xcb geometry\n");
+        return AVERROR(EIO);
+    }

     if (c->x + c->width > geo->width ||
         c->y + c->height > geo->height) {
--
2.20.1

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