From: Pierre Ossman <ossman@cendio.se>
Date: Tue, 24 Sep 2019 07:41:07 +0000 (+0200)
Subject: Be defensive about overflows in stream objects
X-Git-Tag: v1.10.1~4
X-Git-Url: https://source.dussan.org/?a=commitdiff_plain;h=9b9c66d43e16104fa1028df1071fb2b5a338259a;p=tigervnc.git

Be defensive about overflows in stream objects

We use a lot of lengths given to us over the network, so be more
paranoid about them causing an overflow as otherwise an attacker
might trick us in to overwriting other memory.

This primarily affects the client which often gets lengths from the
server, but there are also some scenarios where the server might
theoretically be vulnerable.

Issue found by Pavel Cheremushkin from Kaspersky Lab.

(cherry picked from commit 75e6e0653a48baf474fd45d78b1da53e2f324642)
---

diff --git a/common/rdr/FdInStream.cxx b/common/rdr/FdInStream.cxx
index 9e84ab7a..1730d6d1 100644
--- a/common/rdr/FdInStream.cxx
+++ b/common/rdr/FdInStream.cxx
@@ -136,7 +136,7 @@ size_t FdInStream::overrun(size_t itemSize, size_t nItems, bool wait)
   ptr = start;
 
   size_t bytes_to_read;
-  while (end < start + itemSize) {
+  while ((size_t)(end - start) < itemSize) {
     bytes_to_read = start + bufSize - end;
     if (!timing) {
       // When not timing, we must be careful not to read too much
@@ -152,8 +152,10 @@ size_t FdInStream::overrun(size_t itemSize, size_t nItems, bool wait)
     end += n;
   }
 
-  if (itemSize * nItems > (size_t)(end - ptr))
-    nItems = (end - ptr) / itemSize;
+  size_t nAvail;
+  nAvail = (end - ptr) / itemSize;
+  if (nAvail < nItems)
+    return nAvail;
 
   return nItems;
 }
diff --git a/common/rdr/FdOutStream.cxx b/common/rdr/FdOutStream.cxx
index 1757dc35..f5d07e4b 100644
--- a/common/rdr/FdOutStream.cxx
+++ b/common/rdr/FdOutStream.cxx
@@ -149,9 +149,10 @@ size_t FdOutStream::overrun(size_t itemSize, size_t nItems)
     }
   }
 
-  // Can we fit all the items asked for?
-  if (itemSize * nItems > (size_t)(end - ptr))
-    nItems = (end - ptr) / itemSize;
+  size_t nAvail;
+  nAvail = (end - ptr) / itemSize;
+  if (nAvail < nItems)
+    return nAvail;
 
   return nItems;
 }
diff --git a/common/rdr/FileInStream.cxx b/common/rdr/FileInStream.cxx
index 94f5db88..bdb05a3a 100644
--- a/common/rdr/FileInStream.cxx
+++ b/common/rdr/FileInStream.cxx
@@ -68,7 +68,7 @@ size_t FileInStream::overrun(size_t itemSize, size_t nItems, bool wait)
   ptr = b;
 
 
-  while (end < b + itemSize) {
+  while ((size_t)(end - b) < itemSize) {
     size_t n = fread((U8 *)end, b + sizeof(b) - end, 1, file);
     if (n == 0) {
       if (ferror(file))
@@ -80,8 +80,10 @@ size_t FileInStream::overrun(size_t itemSize, size_t nItems, bool wait)
     end += b + sizeof(b) - end;
   }
 
-  if (itemSize * nItems > (size_t)(end - ptr))
-    nItems = (end - ptr) / itemSize;
+  size_t nAvail;
+  nAvail = (end - ptr) / itemSize;
+  if (nAvail < nItems)
+    return nAvail;
 
   return nItems;
 }
diff --git a/common/rdr/HexInStream.cxx b/common/rdr/HexInStream.cxx
index 8f939889..a6bc92cd 100644
--- a/common/rdr/HexInStream.cxx
+++ b/common/rdr/HexInStream.cxx
@@ -91,7 +91,7 @@ size_t HexInStream::overrun(size_t itemSize, size_t nItems, bool wait) {
   offset += ptr - start;
   ptr = start;
 
-  while (end < ptr + itemSize) {
+  while ((size_t)(end - ptr) < itemSize) {
     size_t n = in_stream.check(2, 1, wait);
     if (n == 0) return 0;
     const U8* iptr = in_stream.getptr();
@@ -110,8 +110,10 @@ size_t HexInStream::overrun(size_t itemSize, size_t nItems, bool wait) {
     end += length;
   }
 
-  if (itemSize * nItems > (size_t)(end - ptr))
-    nItems = (end - ptr) / itemSize;
+  size_t nAvail;
+  nAvail = (end - ptr) / itemSize;
+  if (nAvail < nItems)
+    return nAvail;
 
   return nItems;
 }
diff --git a/common/rdr/HexOutStream.cxx b/common/rdr/HexOutStream.cxx
index 7232514c..eac2eff8 100644
--- a/common/rdr/HexOutStream.cxx
+++ b/common/rdr/HexOutStream.cxx
@@ -102,8 +102,10 @@ HexOutStream::overrun(size_t itemSize, size_t nItems) {
 
   writeBuffer();
 
-  if (itemSize * nItems > (size_t)(end - ptr))
-    nItems = (end - ptr) / itemSize;
+  size_t nAvail;
+  nAvail = (end - ptr) / itemSize;
+  if (nAvail < nItems)
+    return nAvail;
 
   return nItems;
 }
diff --git a/common/rdr/InStream.h b/common/rdr/InStream.h
index 14ecf093..f71a4d9e 100644
--- a/common/rdr/InStream.h
+++ b/common/rdr/InStream.h
@@ -43,12 +43,15 @@ namespace rdr {
 
     inline size_t check(size_t itemSize, size_t nItems=1, bool wait=true)
     {
-      if (ptr + itemSize * nItems > end) {
-        if (ptr + itemSize > end)
-          return overrun(itemSize, nItems, wait);
+      size_t nAvail;
+
+      if (itemSize > (size_t)(end - ptr))
+        return overrun(itemSize, nItems, wait);
+
+      nAvail = (end - ptr) / itemSize;
+      if (nAvail < nItems)
+        return nAvail;
 
-        nItems = (end - ptr) / itemSize;
-      }
       return nItems;
     }
 
@@ -93,13 +96,12 @@ namespace rdr {
     // readBytes() reads an exact number of bytes.
 
     void readBytes(void* data, size_t length) {
-      U8* dataPtr = (U8*)data;
-      U8* dataEnd = dataPtr + length;
-      while (dataPtr < dataEnd) {
-        size_t n = check(1, dataEnd - dataPtr);
-        memcpy(dataPtr, ptr, n);
+      while (length > 0) {
+        size_t n = check(1, length);
+        memcpy(data, ptr, n);
         ptr += n;
-        dataPtr += n;
+        data = (U8*)data + n;
+        length -= n;
       }
     }
 
diff --git a/common/rdr/MemOutStream.h b/common/rdr/MemOutStream.h
index 4a815b30..b56bac3a 100644
--- a/common/rdr/MemOutStream.h
+++ b/common/rdr/MemOutStream.h
@@ -23,6 +23,7 @@
 #ifndef __RDR_MEMOUTSTREAM_H__
 #define __RDR_MEMOUTSTREAM_H__
 
+#include <rdr/Exception.h>
 #include <rdr/OutStream.h>
 
 namespace rdr {
@@ -65,6 +66,9 @@ namespace rdr {
       if (len < (size_t)(end - start) * 2)
         len = (end - start) * 2;
 
+      if (len < (size_t)(end - start))
+        throw Exception("Overflow in MemOutStream::overrun()");
+
       U8* newStart = new U8[len];
       memcpy(newStart, start, ptr - start);
       ptr = newStart + (ptr - start);
diff --git a/common/rdr/OutStream.h b/common/rdr/OutStream.h
index 11aafd2d..0f60ccc1 100644
--- a/common/rdr/OutStream.h
+++ b/common/rdr/OutStream.h
@@ -46,12 +46,15 @@ namespace rdr {
 
     inline size_t check(size_t itemSize, size_t nItems=1)
     {
-      if (ptr + itemSize * nItems > end) {
-        if (ptr + itemSize > end)
-          return overrun(itemSize, nItems);
+      size_t nAvail;
+
+      if (itemSize > (size_t)(end - ptr))
+        return overrun(itemSize, nItems);
+
+      nAvail = (end - ptr) / itemSize;
+      if (nAvail < nItems)
+        return nAvail;
 
-        nItems = (end - ptr) / itemSize;
-      }
       return nItems;
     }
 
@@ -91,13 +94,12 @@ namespace rdr {
     // writeBytes() writes an exact number of bytes.
 
     void writeBytes(const void* data, size_t length) {
-      const U8* dataPtr = (const U8*)data;
-      const U8* dataEnd = dataPtr + length;
-      while (dataPtr < dataEnd) {
-        size_t n = check(1, dataEnd - dataPtr);
-        memcpy(ptr, dataPtr, n);
+      while (length > 0) {
+        size_t n = check(1, length);
+        memcpy(ptr, data, n);
         ptr += n;
-        dataPtr += n;
+        data = (U8*)data + n;
+        length -= n;
       }
     }
 
diff --git a/common/rdr/RandomStream.cxx b/common/rdr/RandomStream.cxx
index d5f1cc85..1be9b251 100644
--- a/common/rdr/RandomStream.cxx
+++ b/common/rdr/RandomStream.cxx
@@ -126,8 +126,10 @@ size_t RandomStream::overrun(size_t itemSize, size_t nItems, bool wait) {
       *(U8*)end++ = (int) (256.0*rand()/(RAND_MAX+1.0));
   }
 
-  if (itemSize * nItems > (size_t)(end - ptr))
-    nItems = (end - ptr) / itemSize;
+  size_t nAvail;
+  nAvail = (end - ptr) / itemSize;
+  if (nAvail < nItems)
+    return nAvail;
 
   return nItems;
 }
diff --git a/common/rdr/TLSInStream.cxx b/common/rdr/TLSInStream.cxx
index d0f94263..3e1172f1 100644
--- a/common/rdr/TLSInStream.cxx
+++ b/common/rdr/TLSInStream.cxx
@@ -43,7 +43,7 @@ ssize_t TLSInStream::pull(gnutls_transport_ptr_t str, void* data, size_t size)
       return -1;
     }
 
-    if (in->getend() - in->getptr() < (ptrdiff_t)size)
+    if ((size_t)(in->getend() - in->getptr()) < size)
       size = in->getend() - in->getptr();
   
     in->readBytes(data, size);
@@ -92,15 +92,17 @@ size_t TLSInStream::overrun(size_t itemSize, size_t nItems, bool wait)
   end -= ptr - start;
   ptr = start;
 
-  while (end < start + itemSize) {
+  while ((size_t)(end - start) < itemSize) {
     size_t n = readTLS((U8*) end, start + bufSize - end, wait);
     if (!wait && n == 0)
       return 0;
     end += n;
   }
 
-  if (itemSize * nItems > (size_t)(end - ptr))
-    nItems = (end - ptr) / itemSize;
+  size_t nAvail;
+  nAvail = (end - ptr) / itemSize;
+  if (nAvail < nItems)
+    return nAvail;
 
   return nItems;
 }
diff --git a/common/rdr/TLSOutStream.cxx b/common/rdr/TLSOutStream.cxx
index 30c456fe..7d7c3b56 100644
--- a/common/rdr/TLSOutStream.cxx
+++ b/common/rdr/TLSOutStream.cxx
@@ -100,8 +100,10 @@ size_t TLSOutStream::overrun(size_t itemSize, size_t nItems)
 
   flush();
 
-  if (itemSize * nItems > (size_t)(end - ptr))
-    nItems = (end - ptr) / itemSize;
+  size_t nAvail;
+  nAvail = (end - ptr) / itemSize;
+  if (nAvail < nItems)
+    return nAvail;
 
   return nItems;
 }
diff --git a/common/rdr/ZlibInStream.cxx b/common/rdr/ZlibInStream.cxx
index e2f971c7..9fcfaf6b 100644
--- a/common/rdr/ZlibInStream.cxx
+++ b/common/rdr/ZlibInStream.cxx
@@ -113,8 +113,10 @@ size_t ZlibInStream::overrun(size_t itemSize, size_t nItems, bool wait)
       return 0;
   }
 
-  if (itemSize * nItems > (size_t)(end - ptr))
-    nItems = (end - ptr) / itemSize;
+  size_t nAvail;
+  nAvail = (end - ptr) / itemSize;
+  if (nAvail < nItems)
+    return nAvail;
 
   return nItems;
 }
diff --git a/common/rdr/ZlibOutStream.cxx b/common/rdr/ZlibOutStream.cxx
index 26a11315..7a0d692c 100644
--- a/common/rdr/ZlibOutStream.cxx
+++ b/common/rdr/ZlibOutStream.cxx
@@ -130,8 +130,10 @@ size_t ZlibOutStream::overrun(size_t itemSize, size_t nItems)
     }
   }
 
-  if (itemSize * nItems > (size_t)(end - ptr))
-    nItems = (end - ptr) / itemSize;
+  size_t nAvail;
+  nAvail = (end - ptr) / itemSize;
+  if (nAvail < nItems)
+    return nAvail;
 
   return nItems;
 }