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bound BMF block walk to buffer end #1643

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45 changes: 33 additions & 12 deletions modules/commodetto/cfeBMF.c
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Original file line number Diff line number Diff line change
Expand Up @@ -77,7 +77,7 @@ void CFELockCache(CommodettoFontEngine bmf, uint8_t lock)

void CFESetFontData(CommodettoFontEngine bmf, const void *fontData, uint32_t fontDataSize)
{
const unsigned char *bytes, *start;
const unsigned char *bytes, *start, *end;
uint32_t size;
uint8_t version;

Expand All @@ -88,6 +88,10 @@ void CFESetFontData(CommodettoFontEngine bmf, const void *fontData, uint32_t fon

start = fontData;
bytes = start;
end = start + fontDataSize;

if (fontDataSize < 5)
return;

version = c_read8(bytes + 3);
if ((0x42 != c_read8(bytes + 0)) || (0x4D != c_read8(bytes + 1)) || (0x46 != c_read8(bytes + 2)) || ((3 != version) && (4 != version)))
Expand All @@ -102,15 +106,24 @@ void CFESetFontData(CommodettoFontEngine bmf, const void *fontData, uint32_t fon
return;
bytes += 1;

bytes += 4 + c_read32(bytes);
if ((end - bytes) < 4)
return;
size = c_read32(bytes);
if (size > (uint32_t)((end - bytes) - 4))
return;
bytes += 4 + size;

// get lineHeight from block 2
if (2 != c_read8(bytes))
if (((end - bytes) < 1) || (2 != c_read8(bytes)))
return;
bytes += 1;

if ((end - bytes) < 4)
return;
size = c_read32(bytes);
bytes += 4;
if (((end - bytes) < 10) || (size < 8) || (size > (uint32_t)(end - bytes)))
return;

bmf->height = c_read16(bytes);
bytes += 2;
Expand All @@ -125,33 +138,41 @@ void CFESetFontData(CommodettoFontEngine bmf, const void *fontData, uint32_t fon
bytes += size - 8;

// skip block 3
if (3 != c_read8(bytes))
if (((end - bytes) < 1) || (3 != c_read8(bytes)))
return;
bytes += 1;

bytes += 4 + c_read32(bytes);
if ((end - bytes) < 4)
return;
size = c_read32(bytes);
if (size > (uint32_t)((end - bytes) - 4))
return;
bytes += 4 + size;

// use block 4
if (4 != c_read8(bytes))
if (((end - bytes) < 1) || (4 != c_read8(bytes)))
return;
bytes += 1;

bmf->charTable = bytes + 4;
bmf->isContinuous = (0x40 & c_read8(19 + bmf->charTable)) ? 1 : 0;

if ((end - bytes) < 4)
return;
size = c_read32(bytes);
if (size % 20)
if ((size % 20) || (size > (uint32_t)((end - bytes) - 4)))
return;
bmf->charTable = bytes + 4;
bmf->isContinuous = (size && (0x40 & c_read8(19 + bmf->charTable))) ? 1 : 0;
bmf->charCount = size / 20;

#if MODDEF_CFE_KERN
// block 5 - kerning
bytes += 4 + size;
if (5 == c_read8(bytes)) {
if (((end - bytes) >= 1) && (5 == c_read8(bytes))) {
bytes += 1;
if ((end - bytes) < 4)
return;
bmf->kernCount = c_read32(bytes) / 10;
bmf->kernTriples = bytes + 4;
bmf->kernSorted = (0x80 & c_read8(19 + bmf->charTable)) ? 1 : 0;
bmf->kernSorted = (size && (0x80 & c_read8(19 + bmf->charTable))) ? 1 : 0;
}
#endif

Expand Down
32 changes: 24 additions & 8 deletions modules/commodetto/commodettoParseBMF.c
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Original file line number Diff line number Diff line change
Expand Up @@ -24,18 +24,18 @@
#include "xsmc.h"
#include "mc.xs.h" // for xsID_ values

//@@ can read beyond end of provided buffer on malformed data
void xs_parseBMF(xsMachine *the)
{
unsigned char *bytes, *start;
unsigned char *bytes, *start, *end;
uint32_t size;
xsUnsignedValue byteLength;
int charCount;

xsmcGetBufferReadable(xsArg(0), (void **)&bytes, &byteLength);
start = bytes;
end = bytes + byteLength;

if ((0x42 != c_read8(bytes + 0)) || (0x4D != c_read8(bytes + 1)) || (0x46 != c_read8(bytes + 2)) || ((3 != c_read8(bytes + 3)) && (4 != c_read8(bytes + 3))))
if ((byteLength < 5) || (0x42 != c_read8(bytes + 0)) || (0x4D != c_read8(bytes + 1)) || (0x46 != c_read8(bytes + 2)) || ((3 != c_read8(bytes + 3)) && (4 != c_read8(bytes + 3))))
xsUnknownError("Invalid BMF header");
bytes += 4;

Expand All @@ -44,15 +44,24 @@ void xs_parseBMF(xsMachine *the)
xsUnknownError("can't find info block");
bytes += 1;

bytes += 4 + c_read32(bytes);
if ((end - bytes) < 4)
xsUnknownError("truncated BMF");
size = c_read32(bytes);
if (size > (uint32_t)((end - bytes) - 4))
xsUnknownError("truncated BMF");
bytes += 4 + size;

// get lineHeight from block 2
if (2 != c_read8(bytes))
if (((end - bytes) < 1) || (2 != c_read8(bytes)))
xsUnknownError("can't find common block");
bytes += 1;

if ((end - bytes) < 4)
xsUnknownError("truncated BMF");
size = c_read32(bytes);
bytes += 4;
if (((end - bytes) < 10) || (size < 8) || (size > (uint32_t)(end - bytes)))
xsUnknownError("truncated BMF");

xsmcSetInteger(xsResult, c_read16(bytes));
bytes += 2;
Expand All @@ -69,20 +78,27 @@ void xs_parseBMF(xsMachine *the)
bytes += size - 8;

// skip block 3
if (3 != c_read8(bytes))
if (((end - bytes) < 1) || (3 != c_read8(bytes)))
xsUnknownError("can't find pages block");
bytes += 1;

bytes += 4 + c_read32(bytes);
if ((end - bytes) < 4)
xsUnknownError("truncated BMF");
size = c_read32(bytes);
if (size > (uint32_t)((end - bytes) - 4))
xsUnknownError("truncated BMF");
bytes += 4 + size;

// use block 4
if (4 != c_read8(bytes))
if (((end - bytes) < 1) || (4 != c_read8(bytes)))
xsUnknownError("can't find chars block");
bytes += 1;

xsmcSetInteger(xsResult, bytes - start);
xsmcDefine(xsArg(0), xsID_position, xsResult, xsDontDelete | xsDontSet);

if ((end - bytes) < 4)
xsUnknownError("truncated BMF");
size = c_read32(bytes);
if (size % 20)
xsUnknownError("bad chars block size");
Expand Down