astc: Return zero on out of bound bits

Avoid out of bound reads on invalid ASTC textures.
Games can bind invalid textures that make us read or write out of bounds.

src/video_core/textures/astc.cpp

@@ -42,21 +42,24 @@ constexpr u32 Popcnt(u32 n) {
 
 class InputBitStream {
 public:
-    constexpr explicit InputBitStream(const u8* ptr, std::size_t start_offset = 0)
-        : cur_byte{ptr}, next_bit{start_offset % 8} {}
+    constexpr explicit InputBitStream(std::span<const u8> data, size_t start_offset = 0)
+        : cur_byte{data.data()}, total_bits{data.size()}, next_bit{start_offset % 8} {}
 
-    constexpr std::size_t GetBitsRead() const {
+    constexpr size_t GetBitsRead() const {
         return bits_read;
     }
 
     constexpr bool ReadBit() {
-        const bool bit = (*cur_byte >> next_bit++) & 1;
+        if (bits_read >= total_bits * 8) {
+            return 0;
+        }
+        const bool bit = ((*cur_byte >> next_bit) & 1) != 0;
+        ++next_bit;
         while (next_bit >= 8) {
             next_bit -= 8;
-            cur_byte++;
+            ++cur_byte;
         }
-
-        bits_read++;
+        ++bits_read;
         return bit;
     }
 
@@ -79,8 +82,9 @@ public:
 
 private:
     const u8* cur_byte;
-    std::size_t next_bit = 0;
-    std::size_t bits_read = 0;
+    size_t total_bits = 0;
+    size_t next_bit = 0;
+    size_t bits_read = 0;
 };
 
 class OutputBitStream {
@@ -200,8 +204,8 @@ using IntegerEncodedVector = boost::container::static_vector<
 
 static void DecodeTritBlock(InputBitStream& bits, IntegerEncodedVector& result, u32 nBitsPerValue) {
     // Implement the algorithm in section C.2.12
-    u32 m[5];
-    u32 t[5];
+    std::array<u32, 5> m;
+    std::array<u32, 5> t;
     u32 T;
 
     // Read the trit encoded block according to
@@ -866,7 +870,7 @@ public:
     }
 };
 
-static void DecodeColorValues(u32* out, u8* data, const u32* modes, const u32 nPartitions,
+static void DecodeColorValues(u32* out, std::span<u8> data, const u32* modes, const u32 nPartitions,
                               const u32 nBitsForColorData) {
     // First figure out how many color values we have
     u32 nValues = 0;
@@ -898,7 +902,7 @@ static void DecodeColorValues(u32* out, u8* data, const u32* modes, const u32 nP
     // We now have enough to decode our integer sequence.
     IntegerEncodedVector decodedColorValues;
 
-    InputBitStream colorStream(data);
+    InputBitStream colorStream(data, 0);
     DecodeIntegerSequence(decodedColorValues, colorStream, range, nValues);
 
     // Once we have the decoded values, we need to dequantize them to the 0-255 range
@@ -1441,7 +1445,7 @@ static void ComputeEndpos32s(Pixel& ep1, Pixel& ep2, const u32*& colorValues,
 
 static void DecompressBlock(std::span<const u8, 16> inBuf, const u32 blockWidth,
                             const u32 blockHeight, std::span<u32, 12 * 12> outBuf) {
-    InputBitStream strm(inBuf.data());
+    InputBitStream strm(inBuf);
     TexelWeightParams weightParams = DecodeBlockInfo(strm);
 
     // Was there an error?
@@ -1619,15 +1623,16 @@ static void DecompressBlock(std::span<const u8, 16> inBuf, const u32 blockWidth,
 
     // Make sure that higher non-texel bits are set to zero
     const u32 clearByteStart = (weightParams.GetPackedBitSize() >> 3) + 1;
-    if (clearByteStart > 0) {
+    if (clearByteStart > 0 && clearByteStart <= texelWeightData.size()) {
         texelWeightData[clearByteStart - 1] &=
             static_cast<u8>((1 << (weightParams.GetPackedBitSize() % 8)) - 1);
+        std::memset(texelWeightData.data() + clearByteStart, 0,
+                    std::min(16U - clearByteStart, 16U));
     }
-    std::memset(texelWeightData.data() + clearByteStart, 0, std::min(16U - clearByteStart, 16U));
 
     IntegerEncodedVector texelWeightValues;
 
-    InputBitStream weightStream(texelWeightData.data());
+    InputBitStream weightStream(texelWeightData);
 
     DecodeIntegerSequence(texelWeightValues, weightStream, weightParams.m_MaxWeight,
                           weightParams.GetNumWeightValues());