Fix heap buffer overflow in sbrDecoder_AssignQmfChannels2SbrChannels().

In the bug the SBR decoder has already set up 9 channels and tries to
allocate one more channel. The assignment of the QMF channels to SBR
channels fails since the QMF domain manages only 8+1 channels instead
of 10 channels as reqeusted by SBR.
Here we have added a check in sbrDecoder_InitElement() which will
return with a parse error in case additional SBR channels would exceed
the maximum number of SBR channels. This solves the potential heap
buffer overflow.

Bug: 158762825
Test: atest DecoderTestAacDrc DecoderTestAacFormat DecoderTestXheAac
Change-Id: I0150ac6d5a47ffce883010f531928656eebc619e

1 files changed, 6 insertions, 6 deletions

diff --git a/libSBRdec/src/sbrdecoder.cpp b/libSBRdec/src/sbrdecoder.cpp
index b51461d..b101a4a 100644
--- a/libSBRdec/src/sbrdecoder.cpp
+++ b/libSBRdec/src/sbrdecoder.cpp
@@ -1,7 +1,7 @@
 /* -----------------------------------------------------------------------------
 Software License for The Fraunhofer FDK AAC Codec Library for Android
 
-© Copyright  1995 - 2019 Fraunhofer-Gesellschaft zur Förderung der angewandten
+© Copyright  1995 - 2020 Fraunhofer-Gesellschaft zur Förderung der angewandten
 Forschung e.V. All rights reserved.
 
  1.    INTRODUCTION
@@ -617,10 +617,6 @@ SBR_ERROR sbrDecoder_InitElement(
       self->numSbrChannels -= self->pSbrElement[elementIndex]->nChannels;
     }
 
-    /* Save element ID for sanity checks and to have a fallback for concealment.
-     */
-    self->pSbrElement[elementIndex]->elementID = elementID;
-
     /* Determine amount of channels for this element */
     switch (elementID) {
       case ID_NONE:
@@ -653,12 +649,16 @@ SBR_ERROR sbrDecoder_InitElement(
     }
 
     /* Sanity check to avoid memory leaks */
-    if (elChannels < self->pSbrElement[elementIndex]->nChannels) {
+    if (elChannels < self->pSbrElement[elementIndex]->nChannels ||
+        (self->numSbrChannels + elChannels) > (8) + (1)) {
       self->numSbrChannels += self->pSbrElement[elementIndex]->nChannels;
       sbrError = SBRDEC_PARSE_ERROR;
       goto bail;
     }
 
+    /* Save element ID for sanity checks and to have a fallback for concealment.
+     */
+    self->pSbrElement[elementIndex]->elementID = elementID;
     self->pSbrElement[elementIndex]->nChannels = elChannels;
 
     for (ch = 0; ch < elChannels; ch++) {