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Handle empty Tight gradient rects

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We always assumed there would be one pixel per row so a rect with
a zero width would result in us writing to unknown memory.

This could theoretically be used by a malicious server to inject
code in to the viewer process.

Issue found by Pavel Cheremushkin from Kaspersky Lab.
This commit is contained in:
Pierre Ossman 2019-09-10 15:36:42 +02:00 committed by Lauri Kasanen
parent 6a3f711878
commit 1224cbdc21
1 changed files with 21 additions and 16 deletions
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37
common/rfb/tightDecode.h
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@ -56,15 +56,17 @@ TightDecoder::FilterGradient24(const rdr::U8 *inbuf,
int rectWidth = r.width();
for (y = 0; y < rectHeight; y++) {
/* First pixel in a row */
for (c = 0; c < 3; c++) {
pix[c] = inbuf[y*rectWidth*3+c] + prevRow[c];
thisRow[c] = pix[c];
}
pf.bufferFromRGB((rdr::U8*)&outbuf[y*stride], pix, 1);
for (x = 0; x < rectWidth; x++) {
/* First pixel in a row */
if (x == 0) {
for (c = 0; c < 3; c++) {
pix[c] = inbuf[y*rectWidth*3+c] + prevRow[c];
thisRow[c] = pix[c];
}
pf.bufferFromRGB((rdr::U8*)&outbuf[y*stride], pix, 1);
continue;
}
/* Remaining pixels of a row */
for (x = 1; x < rectWidth; x++) {
for (c = 0; c < 3; c++) {
est[c] = prevRow[x*3+c] + pix[c] - prevRow[(x-1)*3+c];
if (est[c] > 0xff) {
@ -103,17 +105,20 @@ void TightDecoder::FilterGradient(const rdr::U8* inbuf,
int rectWidth = r.width();
for (y = 0; y < rectHeight; y++) {
/* First pixel in a row */
pf.rgbFromBuffer(pix, &inbuf[y*rectWidth], 1);
for (c = 0; c < 3; c++)
pix[c] += prevRow[c];
for (x = 0; x < rectWidth; x++) {
/* First pixel in a row */
if (x == 0) {
pf.rgbFromBuffer(pix, &inbuf[y*rectWidth], 1);
for (c = 0; c < 3; c++)
pix[c] += prevRow[c];
memcpy(thisRow, pix, sizeof(pix));
memcpy(thisRow, pix, sizeof(pix));
pf.bufferFromRGB((rdr::U8*)&outbuf[y*stride], pix, 1);
pf.bufferFromRGB((rdr::U8*)&outbuf[y*stride], pix, 1);
continue;
}
/* Remaining pixels of a row */
for (x = 1; x < rectWidth; x++) {
for (c = 0; c < 3; c++) {
est[c] = prevRow[x*3+c] + pix[c] - prevRow[(x-1)*3+c];
if (est[c] > 255) {