From c26b4b3bd20b40ca5f1ae9477164473fbd94995d Mon Sep 17 00:00:00 2001 From: Michal Srb Date: Thu, 6 Apr 2017 23:52:22 +0300 Subject: [PATCH] Limit size of cursor accepted by client. Width and height of a cursor are received as U16 from network. Accepting full range of U16 values can cause integer overflows in multiple places. The worst is probably VLA in CMsgReader::readSetXCursor: rdr::U8 buf[width*height*4]; The width*height*4 can be too big to fit on stack or it can overflow into negative numbers. Both cases are undefined behaviour. Following writes to buf can overwrite other data on stack. --- common/rfb/CMsgReader.cxx | 9 +++++++++ common/rfb/CMsgReader.h | 2 ++ 2 files changed, 11 insertions(+) diff --git a/common/rfb/CMsgReader.cxx b/common/rfb/CMsgReader.cxx index 7233fbd7..9abe3f24 100644 --- a/common/rfb/CMsgReader.cxx +++ b/common/rfb/CMsgReader.cxx @@ -202,6 +202,9 @@ void CMsgReader::readRect(const Rect& r, int encoding) void CMsgReader::readSetXCursor(int width, int height, const Point& hotspot) { + if (width > maxCursorSize || height > maxCursorSize) + throw Exception("Too big cursor"); + rdr::U8 pr, pg, pb; rdr::U8 sr, sg, sb; int data_len = ((width+7)/8) * height; @@ -257,6 +260,9 @@ void CMsgReader::readSetXCursor(int width, int height, const Point& hotspot) void CMsgReader::readSetCursor(int width, int height, const Point& hotspot) { + if (width > maxCursorSize || height > maxCursorSize) + throw Exception("Too big cursor"); + int data_len = width * height * (handler->cp.pf().bpp/8); int mask_len = ((width+7)/8) * height; rdr::U8Array data(data_len); @@ -295,6 +301,9 @@ void CMsgReader::readSetCursor(int width, int height, const Point& hotspot) void CMsgReader::readSetCursorWithAlpha(int width, int height, const Point& hotspot) { + if (width > maxCursorSize || height > maxCursorSize) + throw Exception("Too big cursor"); + int encoding; const PixelFormat rgbaPF(32, 32, false, true, 255, 255, 255, 16, 8, 0); diff --git a/common/rfb/CMsgReader.h b/common/rfb/CMsgReader.h index ff73414e..7b52033f 100644 --- a/common/rfb/CMsgReader.h +++ b/common/rfb/CMsgReader.h @@ -69,6 +69,8 @@ namespace rfb { CMsgHandler* handler; rdr::InStream* is; int nUpdateRectsLeft; + + static const int maxCursorSize = 256; }; } #endif -- 2.39.5