avformat/subtitles: add a next line jumper and use it.

This fixes a bunch of possible overread in avformat with the idiom p +=
strcspn(p, "\n") + 1 (strcspn() can focus on the trailing '\0' if no
'\n' is found, so the +1 leads to an overread).

Note on lavf/matroskaenc: no extra subtitles.o Makefile dependency is
added because only the header is required for ff_subtitles_next_line().

Note on lavf/mpsubdec: code gets slightly complex to avoid an infinite
loop in the probing since there is no more forced increment.

NOTE:
Code of function ff_subtitles_next_line fixed by Alexander Strasser.

The original code from master did test the wrong character, but was
corrected by a subsequent commit. That commit however is not backported,
so it had to be fixed in this commit for the backport.

Conflicts:
	libavformat/mpl2dec.c

(cherry picked from commit 90fc00a623de44e137fe1601b91356e8cd8bdd54)

Signed-off-by: Alexander Strasser <eclipse7@gmx.net>

1 files changed, 1 insertions, 1 deletions

diff --git a/libavformat/mpl2dec.c b/libavformat/mpl2dec.c
index ce2061bb8b..2f708e0194 100644
--- a/libavformat/mpl2dec.c
+++ b/libavformat/mpl2dec.c
@@ -43,7 +43,7 @@ static int mpl2_probe(AVProbeData *p)
         if (sscanf(ptr, "[%"PRId64"][%"PRId64"]%c", &start, &end, &c) != 3 &&
             sscanf(ptr, "[%"PRId64"][]%c",          &start,       &c) != 2)
             return 0;
-        ptr += strcspn(ptr, "\r\n") + 1;
+        ptr += ff_subtitles_next_line(ptr);
         if (ptr >= ptr_end)
             return 0;
     }