bmv: check for len being valid in bmv_decode_frame().

It can be 0 or -1 for invalid files, which may result in invalid memory
access.

Reported-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org
(cherry picked from commit b88f902125ee808c8366e9dcb3f21e4c227483fc)

Conflicts:

	libavcodec/bmv.c

diff --git a/libavcodec/bmv.c b/libavcodec/bmv.c
index 49346a41a8d5dde1777d5ab4a01b184bb0de869c..920e75255fd643ca1ef472a6a264307b4f426391 100644 (file)
--- a/libavcodec/bmv.c
+++ b/libavcodec/bmv.c
@@ -134,7 +134,7 @@ static int decode_bmv_frame(const uint8_t *source, int src_len, uint8_t *frame,
         mode += 1 + advance_mode;
         if (mode >= 4)
             mode -= 3;
-        if (FFABS(dst_end - dst) < len)
+        if (len <= 0 || FFABS(dst_end - dst) < len)
             return -1;
         switch (mode) {
         case 1: