From: Erik de Castro Lopo <erikd@mega-nerd.com>

Date: Sun, 25 Aug 2019 07:50:36 +0000 (+1000)

Subject: libFLAC/bitreader.c: Fix shift invoking undefined behaviour

X-Git-Url: http://git.xiph.org/?p=flac.git;a=commitdiff_plain;h=8147ee7ea214195bddab403840c95d4c748bfedc

libFLAC/bitreader.c: Fix shift invoking undefined behaviour

Credit: Oss-Fuzz

Issue: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=16464

Testcase: fuzzer_decoder-5663276452544512

---

diff --git a/src/libFLAC/bitreader.c b/src/libFLAC/bitreader.c

index 62e11991..5e4b5918 100644

--- a/src/libFLAC/bitreader.c

+++ b/src/libFLAC/bitreader.c

@@ -119,8 +119,10 @@ static inline void crc16_update_word_(FLAC__BitReader *br, brword word)

{

register uint32_t crc = br->read_crc16;

- for( ; br->crc16_align < FLAC__BITS_PER_WORD; br->crc16_align += 8)

- crc = FLAC__CRC16_UPDATE((uint32_t)((word >> (FLAC__BITS_PER_WORD-8-br->crc16_align)) & 0xff), crc);

+ for ( ; br->crc16_align < FLAC__BITS_PER_WORD ; br->crc16_align += 8) {

+ uint32_t shift = FLAC__BITS_PER_WORD - 8 - br->crc16_align ;

+ crc = FLAC__CRC16_UPDATE ((uint32_t) (shift < FLAC__BITS_PER_WORD ? (word >> shift) & 0xff : 0), crc);

+ }

br->read_crc16 = crc;

br->crc16_align = 0;