From 4e944af756ec44e73b78bbed84a01fa9d2dfa5f5 Mon Sep 17 00:00:00 2001
From: Martin Storsjo <martin@martin.st>
Date: Tue, 17 Nov 2020 12:15:20 +0200
Subject: [PATCH] Avoid undefined shifts in SBR calcCRC

Fixes: 25404/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_LIBFDK_AAC_fuzzer-5397024709804032

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
---
 libSBRdec/src/sbr_crc.cpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/libSBRdec/src/sbr_crc.cpp b/libSBRdec/src/sbr_crc.cpp
index ba0fd05..8a5282e 100644
--- a/libSBRdec/src/sbr_crc.cpp
+++ b/libSBRdec/src/sbr_crc.cpp
@@ -153,8 +153,10 @@ static int getCrc(HANDLE_FDK_BITSTREAM hBs, ULONG NrBits) {
     calcCRC(&CrcBuf, bValue, MAXCRCSTEP);
   }
 
-  bValue = FDKreadBits(hBs, CrcNrBitsRest);
-  calcCRC(&CrcBuf, bValue, CrcNrBitsRest);
+  if (CrcNrBitsRest > 0) {
+    bValue = FDKreadBits(hBs, CrcNrBitsRest);
+    calcCRC(&CrcBuf, bValue, CrcNrBitsRest);
+  }
 
   return (CrcBuf.crcState & SBR_CRC_RANGE);
 }