mov: Add an option to toggle dref opening

This feature is mostly only used by NLE software, and is
both of dubious value being enabled by default, and a
possible security risk.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

libavformat/isom.h

@@ -159,6 +159,7 @@ typedef struct MOVContext {
     int64_t next_root_atom; ///< offset of the next root atom
     int export_all;
     int export_xmp;
+    int enable_drefs;
 } MOVContext;
 
 int ff_mp4_read_descr_len(AVIOContext *pb);

libavformat/mov.c

@@ -2484,12 +2484,22 @@ static int mov_read_trak(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 
     if (sc->dref_id-1 < sc->drefs_count && sc->drefs[sc->dref_id-1].path) {
         MOVDref *dref = &sc->drefs[sc->dref_id - 1];
+        if (c->enable_drefs) {
             if (mov_open_dref(&sc->pb, c->fc->filename, dref, &c->fc->interrupt_callback) < 0)
                 av_log(c->fc, AV_LOG_ERROR,
                        "stream %d, error opening alias: path='%s', dir='%s', "
                        "filename='%s', volume='%s', nlvl_from=%d, nlvl_to=%d\n",
                        st->index, dref->path, dref->dir, dref->filename,
                        dref->volume, dref->nlvl_from, dref->nlvl_to);
+        } else {
+            av_log(c->fc, AV_LOG_WARNING,
+                   "Skipped opening external track: "
+                   "stream %d, alias: path='%s', dir='%s', "
+                   "filename='%s', volume='%s', nlvl_from=%d, nlvl_to=%d."
+                   "Set enable_drefs to allow this.\n",
+                   st->index, dref->path, dref->dir, dref->filename,
+                   dref->volume, dref->nlvl_from, dref->nlvl_to);
+        }
     } else
         sc->pb = c->fc->pb;
 
@@ -3643,6 +3653,8 @@ static const AVOption mov_options[] = {
         AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 1, .flags = FLAGS },
     { "export_xmp", "Export full XMP metadata", OFFSET(export_xmp),
         AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 1, .flags = FLAGS },
+    { "enable_drefs", "Enable external track support.", OFFSET(enable_drefs),
+        AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 1, .flags = FLAGS },
     { NULL },
 };
 

libavformat/version.h

@@ -30,7 +30,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVFORMAT_VERSION_MAJOR 57
-#define LIBAVFORMAT_VERSION_MINOR  2
+#define LIBAVFORMAT_VERSION_MINOR  3
 #define LIBAVFORMAT_VERSION_MICRO  0
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \