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[FFmpeg-devel,3/5] avformat/webmdashenc: Remove possibility of infinite loop

Message ID 20200518033033.27347-3-andreas.rheinhardt@gmail.com
State Accepted
Commit 9b614826275e346ac17b9bc7ef5a58dded5b1855
Headers show
Series [FFmpeg-devel,1/5] avformat/webmdashenc: Avoid allocation for parsing a number
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Commit Message

Andreas Rheinhardt May 18, 2020, 3:30 a.m. UTC
The WebM DASH manifest muxer uses a loop to parse the adaptation_sets
string (which is given by the user and governs which AVStreams are
mapped to what adaptation set) and the very beginning of this loop is
"if (*p == ' ') continue;". This of course leads to an infinite loop if
the condition is true. It is true if e.g. the string begins with ' ' or
if there are more than one ' ' between different adaptation set groups.

To fix this, the parsing process has been modified to consume the space
if it is at a place where it can legitimately occur, i.e. when a new
adaptation set group is expected. The latter restriction implies that an
error is returned if a space exists where none is allowed to exist.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
---
 libavformat/webmdashenc.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
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Patch

diff --git a/libavformat/webmdashenc.c b/libavformat/webmdashenc.c
index 250c8ca3ad..fd07b3e34a 100644
--- a/libavformat/webmdashenc.c
+++ b/libavformat/webmdashenc.c
@@ -438,9 +438,10 @@  static int parse_adaptation_sets(AVFormatContext *s)
     // syntax id=0,streams=0,1,2 id=1,streams=3,4 and so on
     state = new_set;
     while (p < w->adaptation_sets + strlen(w->adaptation_sets)) {
-        if (*p == ' ')
+        if (state == new_set && *p == ' ') {
+            p++;
             continue;
-        else if (state == new_set && !strncmp(p, "id=", 3)) {
+        } else if (state == new_set && !strncmp(p, "id=", 3)) {
             void *mem = av_realloc(w->as, sizeof(*w->as) * (w->nb_as + 1));
             const char *comma;
             if (mem == NULL)