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BMP: harden identify checks to avoid misidentification of other datasets (fixes #4713) #4720

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Oct 27, 2021
+28 −6
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BMP: harden identify checks to avoid misidentification of other datasets (fixes #4713) #4720

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34 changes: 28 additions & 6 deletions frmts/bmp/bmpdataset.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -118,6 +118,9 @@ typedef struct
// File header size in bytes:
constexpr int BFH_SIZE = 14;

// Size of sInfoHeader.iSize in bytes
constexpr int SIZE_OF_INFOHEADER_SIZE = 4;

typedef struct
{
GUInt32 iSize; // Size of BMPInfoHeader structure in bytes.
Expand Down Expand Up @@ -1069,9 +1072,20 @@ CPLErr BMPDataset::IRasterIO( GDALRWFlag eRWFlag,
int BMPDataset::Identify( GDALOpenInfo *poOpenInfo )

{
if( poOpenInfo->nHeaderBytes < 2
if( poOpenInfo->nHeaderBytes < BFH_SIZE + SIZE_OF_INFOHEADER_SIZE
|| poOpenInfo->pabyHeader[0] != 'B'
|| poOpenInfo->pabyHeader[1] != 'M' )
|| poOpenInfo->pabyHeader[1] != 'M'
|| poOpenInfo->pabyHeader[6] != 0
|| poOpenInfo->pabyHeader[7] != 0
|| poOpenInfo->pabyHeader[8] != 0
|| poOpenInfo->pabyHeader[9] != 0 )
return FALSE;

uint32_t nInfoHeaderSize;
memcpy(&nInfoHeaderSize, poOpenInfo->pabyHeader + BFH_SIZE, sizeof(uint32_t));
CPL_LSBPTR32(&nInfoHeaderSize);
// Check against the maximum known size
if( nInfoHeaderSize > BIH_OS22SIZE )
return FALSE;

return TRUE;
Expand All @@ -1091,8 +1105,6 @@ GDALDataset *BMPDataset::Open( GDALOpenInfo * poOpenInfo )
/* -------------------------------------------------------------------- */
BMPDataset *poDS = new BMPDataset();
poDS->eAccess = poOpenInfo->eAccess;
poDS->fp = poOpenInfo->fpL;
poOpenInfo->fpL = nullptr;

VSIStatBufL sStat;
if (VSIStatL(poOpenInfo->pszFilename, &sStat) != 0)
Expand All @@ -1104,8 +1116,7 @@ GDALDataset *BMPDataset::Open( GDALOpenInfo * poOpenInfo )
/* -------------------------------------------------------------------- */
/* Read the BMPFileHeader. We need iOffBits value only */
/* -------------------------------------------------------------------- */
VSIFSeekL( poDS->fp, 10, SEEK_SET );
VSIFReadL( &poDS->sFileHeader.iOffBits, 1, 4, poDS->fp );
memcpy( &poDS->sFileHeader.iOffBits, poOpenInfo->pabyHeader + 10, 4 );
#ifdef CPL_MSB
CPL_SWAP32PTR( &poDS->sFileHeader.iOffBits );
#endif
Expand All @@ -1117,9 +1128,20 @@ GDALDataset *BMPDataset::Open( GDALOpenInfo * poOpenInfo )
poDS->sFileHeader.iOffBits );
#endif

// Validatate iOffBits
if( poDS->sFileHeader.iOffBits <= BFH_SIZE + SIZE_OF_INFOHEADER_SIZE ||
poDS->sFileHeader.iOffBits >= poDS->sFileHeader.iSize )
{
delete poDS;
return nullptr;
}

/* -------------------------------------------------------------------- */
/* Read the BMPInfoHeader. */
/* -------------------------------------------------------------------- */
poDS->fp = poOpenInfo->fpL;
poOpenInfo->fpL = nullptr;

VSIFSeekL( poDS->fp, BFH_SIZE, SEEK_SET );
VSIFReadL( &poDS->sInfoHeader.iSize, 1, 4, poDS->fp );
#ifdef CPL_MSB
Expand Down