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Bitstream: Prevent array overreads and undefined behaviour #198

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Merged
JeromeMartinez merged 4 commits into from
Nov 7, 2026
Merged

Bitstream: Prevent array overreads and undefined behaviour #198

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d8beef1
Bitstream: Prevent array overreads and undefined behaviour
cjee21 Jun 3, 2026
6ed5e3e
BitstreamLE: Fix Byte_Align
cjee21 Jun 4, 2026
4117952
Bitstream: Stop bit skips on buffer underrun
cjee21 Nov 4, 2026
2e986ed
BitstreamLE: Preserve previous offset on invalid reads
JeromeMartinez Nov 7, 2026
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2 changes: 2 additions & 0 deletions Source/ZenLib/BitStream.h
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Original file line number Diff line number Diff line change
Expand Up @@ -183,6 +183,8 @@ class BitStream
do
{
Skip(32);
if (BufferUnderRun)
return;
HowMany-=32;
}
while(HowMany>32);
Expand Down
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
24 changes: 21 additions & 3 deletions Source/ZenLib/BitStream_LE.h
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Original file line number Diff line number Diff line change
Expand Up @@ -51,8 +51,6 @@ class BitStream_LE : public BitStream

int32u Get (size_t HowMany)
{
ptr_BeforeLastCall=ptr;

long ret;
static const int32u Mask[33]={
0x00000000,
Expand All @@ -65,6 +63,12 @@ class BitStream_LE : public BitStream
0x01ffffff, 0x03ffffff, 0x07ffffff, 0x0fffffff,
0x1fffffff, 0x3fffffff, 0x7fffffff, 0xffffffff,
};

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

ptr_BeforeLastCall=ptr;

unsigned long m=Mask[HowMany];

HowMany+=endbit;
Expand Down Expand Up @@ -103,6 +107,20 @@ 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);
if (!buffer)
return;
bits-=32;
} while (bits>32);
if (bits)
Get(bits);
return;
}
Get(bits);
}

Expand All @@ -114,7 +132,7 @@ 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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