[FFmpeg-cvslog] avformat/dashdec: Fix crash on invalid input/ENOMEM, fix leak

[Andreas Rheinhardt]

ffmpeg | branch: release/5.1 | Andreas Rheinhardt <andreas.rheinhardt at outlook.com> | Tue Sep 20 22:08:47 2022 +0200| [f202a1fdf75d0e7f48a2e8d63c2d390cc4b19c85] | committer: Andreas Rheinhardt

avformat/dashdec: Fix crash on invalid input/ENOMEM, fix leak

In case a SupplementalProperty node exists in an adaptationset,
it is searched for a "schemeIdUri" property via xmlGetProp().
Whatever xmlGetProp() returns is then compared via av_strcasecmp()
to a string literal. xmlGetProp() can return NULL, namely in case
no "schemeIdUri" exists and (given that this string is allocated)
presumably also on allocation failure. No check for NULL is done,
so this may crash.

Furthermore, the string returned by xmlGetProp() needs to be freed
with xmlFree(), but this is not done either.

This commit fixes both of these issues; they existed since this code
has been added in 10d008f0fd9e713e290f626300d66382ad786c49.

This has been found while investigating ticket #9697. The continuous
leaks might very well be the reason behind the observed slowdown.

Reviewed-by: Steven Liu <lingjiujianke at gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>
(cherry picked from commit 14b3830b33075e92f8e2766c0c53e8b6bc570c6c)

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=f202a1fdf75d0e7f48a2e8d63c2d390cc4b19c85
---

 libavformat/dashdec.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/libavformat/dashdec.c b/libavformat/dashdec.c
index 63bf7e96a5..2ca91bea8b 100644
--- a/libavformat/dashdec.c
+++ b/libavformat/dashdec.c
@@ -956,7 +956,11 @@ static int parse_manifest_representation(AVFormatContext *s, const char *url,
             xmlFree(val);
         }
         if (adaptionset_supplementalproperty_node) {
-            if (!av_strcasecmp(xmlGetProp(adaptionset_supplementalproperty_node,"schemeIdUri"), "http://dashif.org/guidelines/last-segment-number")) {
+            char *scheme_id_uri = xmlGetProp(adaptionset_supplementalproperty_node, "schemeIdUri");
+            if (scheme_id_uri) {
+                int is_last_segment_number = !av_strcasecmp(scheme_id_uri, "http://dashif.org/guidelines/last-segment-number");
+                xmlFree(scheme_id_uri);
+                if (is_last_segment_number) {
                 val = xmlGetProp(adaptionset_supplementalproperty_node,"value");
                 if (!val) {
                     av_log(s, AV_LOG_ERROR, "Missing value attribute in adaptionset_supplementalproperty_node\n");
@@ -965,6 +969,7 @@ static int parse_manifest_representation(AVFormatContext *s, const char *url,
                     xmlFree(val);
                 }
             }
+            }
         }
 
         fragment_timeline_node = find_child_node_by_name(representation_segmenttemplate_node, "SegmentTimeline");