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From 996356b6c65ca165ee1ea46a571c32a1dc3c3821 Mon Sep 17 00:00:00 2001
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From: Pierre Ossman <ossman@cendio.se>
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Date: Tue, 10 Sep 2019 15:21:03 +0200
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Subject: [PATCH] Restrict PixelBuffer dimensions to safe values
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We do a lot of calculations based on pixel coordinates and we need
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to make sure they do not overflow. Restrict the maximum dimensions
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we support rather than try to switch over all calculations to use
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64 bit integers.
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This prevents attackers from from injecting code by specifying a
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huge framebuffer size and relying on the values overflowing to
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access invalid areas of the heap.
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This primarily affects the client which gets both the screen
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dimensions and the pixel contents from the remote side. But the
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server might also be affected as a client can adjust the screen
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dimensions, as can applications inside the session.
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Issue found by Pavel Cheremushkin from Kaspersky Lab.
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---
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common/rfb/PixelBuffer.cxx | 22 ++++++++++++++++++++++
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1 file changed, 22 insertions(+)
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diff --git a/common/rfb/PixelBuffer.cxx b/common/rfb/PixelBuffer.cxx
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index ad58324..18f41f8 100644
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--- a/common/rfb/PixelBuffer.cxx
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+++ b/common/rfb/PixelBuffer.cxx
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@@ -31,6 +31,14 @@ using namespace rdr;
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static LogWriter vlog("PixelBuffer");
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+// We do a lot of byte offset calculations that assume the result fits
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+// inside a signed 32 bit integer. Limit the maximum size of pixel
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+// buffers so that these calculations never overflow.
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+
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+const int maxPixelBufferWidth = 16384;
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+const int maxPixelBufferHeight = 16384;
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+const int maxPixelBufferStride = 16384;
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+
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// -=- Generic pixel buffer class
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@@ -108,6 +116,11 @@ void PixelBuffer::getImage(const PixelFormat& pf, void* imageBuf,
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void PixelBuffer::setSize(int width, int height)
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{
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+ if ((width < 0) || (width > maxPixelBufferWidth))
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+ throw rfb::Exception("Invalid PixelBuffer width of %d pixels requested", width);
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+ if ((height < 0) || (height > maxPixelBufferHeight))
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+ throw rfb::Exception("Invalid PixelBuffer height of %d pixels requested", height);
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+
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width_ = width;
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height_ = height;
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}
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@@ -337,6 +350,15 @@ const rdr::U8* FullFramePixelBuffer::getBuffer(const Rect& r, int* stride_) cons
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void FullFramePixelBuffer::setBuffer(int width, int height,
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rdr::U8* data_, int stride_)
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{
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+ if ((width < 0) || (width > maxPixelBufferWidth))
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+ throw rfb::Exception("Invalid PixelBuffer width of %d pixels requested", width);
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+ if ((height < 0) || (height > maxPixelBufferHeight))
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+ throw rfb::Exception("Invalid PixelBuffer height of %d pixels requested", height);
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+ if ((stride_ < 0) || (stride_ > maxPixelBufferStride) || (stride_ < width))
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+ throw rfb::Exception("Invalid PixelBuffer stride of %d pixels requested", stride_);
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+ if ((width != 0) && (height != 0) && (data_ == NULL))
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+ throw rfb::Exception("PixelBuffer requested without a valid memory area");
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+
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ModifiablePixelBuffer::setSize(width, height);
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stride = stride_;
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data = data_;
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