[FFmpeg-cvslog] avformat/rtsp: Set port_off to zero for low min/max port range

[Andriy Gelman]

ffmpeg | branch: master | Andriy Gelman <andriy.gelman at gmail.com> | Sun Jul  4 11:40:25 2021 -0400| [02387de90e71a6b035e3adf2446b6002ca135511] | committer: Andriy Gelman

avformat/rtsp: Set port_off to zero for low min/max port range

Fixes:
$ ffmpeg -min_port 32000 -max_port 32001 -i rtsp://wowzaec2demo.streamlock.net/vod/mp4:BigBuckBunny_115k.mov -f null -
[1]    303871 floating point exception (core dumped)

Reviewed-by: Martin Storsjö <martin at martin.st>
Signed-off-by: Andriy Gelman <andriy.gelman at gmail.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=02387de90e71a6b035e3adf2446b6002ca135511
---

 libavformat/rtsp.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/libavformat/rtsp.c b/libavformat/rtsp.c
index d4ab8f28bf..f294d0ec24 100644
--- a/libavformat/rtsp.c
+++ b/libavformat/rtsp.c
@@ -1438,7 +1438,7 @@ int ff_rtsp_make_setup_request(AVFormatContext *s, const char *host, int port,
                               int lower_transport, const char *real_challenge)
 {
     RTSPState *rt = s->priv_data;
-    int rtx = 0, j, i, err, interleave = 0, port_off;
+    int rtx = 0, j, i, err, interleave = 0, port_off = 0;
     RTSPStream *rtsp_st;
     RTSPMessageHeader reply1, *reply = &reply1;
     char cmd[MAX_URL_SIZE];
@@ -1457,9 +1457,11 @@ int ff_rtsp_make_setup_request(AVFormatContext *s, const char *host, int port,
     /* Choose a random starting offset within the first half of the
      * port range, to allow for a number of ports to try even if the offset
      * happens to be at the end of the random range. */
+    if (rt->rtp_port_max - rt->rtp_port_min >= 4) {
     port_off = av_get_random_seed() % ((rt->rtp_port_max - rt->rtp_port_min)/2);
     /* even random offset */
     port_off -= port_off & 0x01;
+    }
 
     for (j = rt->rtp_port_min + port_off, i = 0; i < rt->nb_rtsp_streams; ++i) {
         char transport[MAX_URL_SIZE];