From 79f64f7ebc2b2b7030c6219914bc141cc03fd377 Mon Sep 17 00:00:00 2001 From: Luca Barbato Date: Sat, 8 Jul 2017 21:04:44 +0200 Subject: [PATCH] bitstream: Avoid undefined behavior in bitstream_skip() Do not use skip_remaining() to fully wipe the cache, as this could do a 64-bit shift of a 64-bit variable which is undefined behavior in C. Instead set the related variables to zero directly. Thanks to Uoti for pointing out the problem. CC: libav-stable@libav.org --- libavcodec/bitstream.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/libavcodec/bitstream.h b/libavcodec/bitstream.h index d6dd2b9411..1b23cb2fa7 100644 --- a/libavcodec/bitstream.h +++ b/libavcodec/bitstream.h @@ -239,11 +239,13 @@ static inline void skip_remaining(BitstreamContext *bc, unsigned n) /* Skip n bits in the buffer. */ static inline void bitstream_skip(BitstreamContext *bc, unsigned n) { - if (n <= bc->bits_left) + if (n < bc->bits_left) skip_remaining(bc, n); else { n -= bc->bits_left; - skip_remaining(bc, bc->bits_left); + bc->bits = 0; + bc->bits_left = 0; + if (n >= 64) { unsigned skip = n / 8;