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From 69cd6157644cb0a5c9edd7b5920232c2ca31c151 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20P=C3=ADsa=C5=99?= <ppisar@redhat.com>
Date: Tue, 12 Mar 2019 16:21:41 +0100
Subject: [PATCH] CVE-2019-7577: Fix a buffer overread in MS_ADPCM_nibble and
 MS_ADPCM_decode
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

If a chunk of RIFF/WAV file with MS ADPCM encoding contains an invalid
predictor (a valid predictor's value is between 0 and 6 inclusive),
a buffer overread can happen when the predictor is used as an index
into an array of MS ADPCM coefficients.

The overead happens when indexing MS_ADPCM_state.aCoeff[] array in
MS_ADPCM_decode() and later when dereferencing a coef pointer in
MS_ADPCM_nibble().

This patch fixes it by checking the MS ADPCM predictor values fit
into the valid range.

CVE-2019-7577
Reproducer: https://bugzilla.libsdl.org/show_bug.cgi?id=4492

Signed-off-by: Petr Písař <ppisar@redhat.com>
---
 src/audio/SDL_wave.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/audio/SDL_wave.c b/src/audio/SDL_wave.c
index 08f65cb..5f93651 100644
--- a/src/audio/SDL_wave.c
+++ b/src/audio/SDL_wave.c
@@ -155,6 +155,9 @@ static int MS_ADPCM_decode(Uint8 **audio_buf, Uint32 *audio_len)
 		if ( stereo ) {
 			state[1]->hPredictor = *encoded++;
 		}
+		if (state[0]->hPredictor >= 7 || state[1]->hPredictor >= 7) {
+			goto invalid_predictor;
+		}
 		state[0]->iDelta = ((encoded[1]<<8)|encoded[0]);
 		encoded += sizeof(Sint16);
 		if ( stereo ) {
@@ -227,6 +230,10 @@ invalid_size:
 	SDL_SetError("Unexpected chunk length for a MS ADPCM decoder");
 	SDL_free(freeable);
 	return(-1);
+invalid_predictor:
+	SDL_SetError("Invalid predictor value for a MS ADPCM decoder");
+	SDL_free(freeable);
+	return(-1);
 }
 
 struct IMA_ADPCM_decodestate {
-- 
2.20.1