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fix(pnm): use 64-bit scanline math to avoid integer overflow #5344

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fix(pnm): use 64-bit scanline math to avoid integer overflow #5344

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20 changes: 10 additions & 10 deletions src/pnm.imageio/pnminput.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -278,8 +278,16 @@ PNMInput::read_file_scanline(void* data, int y)
}

std::vector<unsigned char> buf;
int nsamples = m_spec.width * m_spec.nchannels;
bool good = true;
imagesize_t width(m_spec.width); // 64 bit to avoid overflow
imagesize_t nsamples = width * m_spec.nchannels;
imagesize_t numbytes;
if (m_pnm_type == P4)
numbytes = (width + 7) / 8;
else if (m_pnm_type == PF || m_pnm_type == Pf)
numbytes = nsamples * 4;
else
numbytes = m_spec.scanline_bytes();
bool good = true;
// If y is farther ahead, skip scanlines to get to it
for (; good && m_y_next <= y; ++m_y_next) {
// PFM files are bottom-to-top, so we need to seek to the right spot
Expand All @@ -293,19 +301,11 @@ PNMInput::read_file_scanline(void* data, int y)

if ((m_pnm_type >= P4 && m_pnm_type <= P6) || m_pnm_type == PF
|| m_pnm_type == Pf) {
int numbytes;
if (m_pnm_type == P4)
numbytes = (m_spec.width + 7) / 8;
else if (m_pnm_type == PF || m_pnm_type == Pf)
numbytes = m_spec.nchannels * 4 * m_spec.width;
else
numbytes = m_spec.scanline_bytes();
if (size_t(numbytes) > m_remaining.size()) {
errorfmt("Premature end of file");
return false;
}
buf.assign(m_remaining.begin(), m_remaining.begin() + numbytes);

m_remaining.remove_prefix(numbytes);
}

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