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Bitstream: Prevent array overreads and undefined behaviour #198

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6e29a4a
Bitstream: Prevent array overreads and undefined behaviour
cjee21 Jun 3, 2026
736e6e4
BitstreamLE: Fix Byte_Align
cjee21 Jun 4, 2026
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18 changes: 18 additions & 0 deletions Source/ZenLib/BitStream_Fast.h
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Original file line number Diff line number Diff line change
Expand Up @@ -80,6 +80,9 @@ class BitStream_Fast
0x1f, 0x3f, 0x7f, 0xff,
};

if (HowMany==0 || HowMany>8)
return 0;

if (HowMany<=(Buffer_Size%8))
{
Buffer_Size-=HowMany;
Expand Down Expand Up @@ -117,6 +120,9 @@ class BitStream_Fast
0x1fff, 0x3fff, 0x7fff, 0xffff,
};

if (HowMany==0 || HowMany>16)
return 0;

if (HowMany<=(Buffer_Size%8))
{
Buffer_Size-=HowMany;
Expand Down Expand Up @@ -164,6 +170,9 @@ class BitStream_Fast
0x1fffffff, 0x3fffffff, 0x7fffffff, 0xffffffff,
};

if (HowMany==0 || HowMany>32)
return 0;

if (HowMany<=(Buffer_Size%8))
{
Buffer_Size-=HowMany;
Expand Down Expand Up @@ -263,6 +272,9 @@ class BitStream_Fast
0x1f, 0x3f, 0x7f, 0xff,
};

if (HowMany==0 || HowMany>8)
return 0;

if (HowMany<=(Buffer_Size%8))
return (LastByte>>((Buffer_Size-HowMany)%8))&Mask[HowMany];

Expand Down Expand Up @@ -295,6 +307,9 @@ class BitStream_Fast
0x1fff, 0x3fff, 0x7fff, 0xffff,
};

if (HowMany==0 || HowMany>16)
return 0;

if (HowMany<=(Buffer_Size%8))
return (LastByte>>((Buffer_Size-HowMany)%8))&Mask[HowMany];

Expand Down Expand Up @@ -341,6 +356,9 @@ class BitStream_Fast
0x1fffffff, 0x3fffffff, 0x7fffffff, 0xffffffff,
};

if (HowMany==0 || HowMany>32)
return 0;

if (HowMany<=(Buffer_Size%8))
return (LastByte>>((Buffer_Size-HowMany)%8))&Mask[HowMany];

Expand Down
18 changes: 17 additions & 1 deletion Source/ZenLib/BitStream_LE.h
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Original file line number Diff line number Diff line change
Expand Up @@ -65,6 +65,10 @@ class BitStream_LE : public BitStream
0x01ffffff, 0x03ffffff, 0x07ffffff, 0x0fffffff,
0x1fffffff, 0x3fffffff, 0x7fffffff, 0xffffffff,
};

if (HowMany==0 || HowMany>32)
return 0;

unsigned long m=Mask[HowMany];

HowMany+=endbit;
Expand Down Expand Up @@ -103,6 +107,18 @@ class BitStream_LE : public BitStream

void Skip(size_t bits)
{
if (bits==0)
return;
if (bits>32) //Get is only for <=32 bits
{
do {
Get(32);
bits-=32;
} while (bits>32);
if (bits)
Get(bits);
return;
}
Get(bits);
}

Expand All @@ -114,7 +130,7 @@ class BitStream_LE : public BitStream
void Byte_Align()
{
if (endbit)
Get(endbit);
Get(8-endbit);
};

size_t Offset_Get()
Expand Down
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