[FFmpeg-cvslog] http: avoid out of bound accesses on broken Set-Cookie headers

[wm4]

ffmpeg | branch: master | wm4 <nfxjfg at googlemail.com> | Thu Mar  8 04:47:40 2018 +0100| [c0687acbf6094053834af6a20e9d71b455842c8c] | committer: wm4

http: avoid out of bound accesses on broken Set-Cookie headers

It's trivial to craft a HTTP response that will make the code for
skipping trailing whitespace access and possibly overwrite bytes outside
of the memory allocation. Why this can happen is blindingly obvious: it
accesses cstr[strlen(cstr)-1] without checking whether the string is
empty.

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=c0687acbf6094053834af6a20e9d71b455842c8c
---

 libavformat/http.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/libavformat/http.c b/libavformat/http.c
index d7a72e7129..59f90ac603 100644
--- a/libavformat/http.c
+++ b/libavformat/http.c
@@ -750,6 +750,9 @@ static int parse_set_cookie(const char *set_cookie, AVDictionary **dict)
 {
     char *param, *next_param, *cstr, *back;
 
+    if (!set_cookie[0])
+        return 0;
+
     if (!(cstr = av_strdup(set_cookie)))
         return AVERROR(EINVAL);