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Make ZlibInStream more robust against failures

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Move the checks around to avoid missing cases where we might access
memory that is no longer valid. Also avoid touching the underlying
stream implicitly (e.g. via the destructor) as it might also no
longer be valid.

A malicious server could theoretically use this for remote code
execution in the client.

Issue found by Pavel Cheremushkin from Kaspersky Lab
This commit is contained in:
Pierre Ossman 2019-09-10 11:05:48 +02:00 committed by Lauri Kasanen
parent ac06594b12
commit 3282836baf
4 changed files with 12 additions and 9 deletions
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13
common/rdr/ZlibInStream.cxx
View File

@ -52,16 +52,16 @@ int ZlibInStream::pos()
return offset + ptr - start;
}
void ZlibInStream::removeUnderlying()
void ZlibInStream::flushUnderlying()
{
ptr = end = start;
if (!underlying) return;
while (bytesIn > 0) {
decompress(true);
end = start; // throw away any data
}
underlying = 0;
setUnderlying(NULL, 0);
}
void ZlibInStream::reset()
@ -90,7 +90,7 @@ void ZlibInStream::init()
void ZlibInStream::deinit()
{
assert(zs != NULL);
removeUnderlying();
setUnderlying(NULL, 0);
inflateEnd(zs);
delete zs;
zs = NULL;
@ -100,8 +100,6 @@ int ZlibInStream::overrun(int itemSize, int nItems, bool wait)
{
if (itemSize > bufSize)
throw Exception("ZlibInStream overrun: max itemSize exceeded");
if (!underlying)
throw Exception("ZlibInStream overrun: no underlying stream");
if (end - ptr != 0)
memmove(start, ptr, end - ptr);
@ -127,6 +125,9 @@ int ZlibInStream::overrun(int itemSize, int nItems, bool wait)
bool ZlibInStream::decompress(bool wait)
{
if (!underlying)
throw Exception("ZlibInStream overrun: no underlying stream");
zs->next_out = (U8*)end;
zs->avail_out = start + bufSize - end;

2
common/rdr/ZlibInStream.h
View File

@ -38,7 +38,7 @@ namespace rdr {
virtual ~ZlibInStream();
void setUnderlying(InStream* is, int bytesIn);
void removeUnderlying();
void flushUnderlying();
int pos();
void reset();

3
common/rfb/TightDecoder.cxx
View File

@ -340,7 +340,8 @@ void TightDecoder::decodeRect(const Rect& r, const void* buffer,
zis[streamId].readBytes(netbuf, dataSize);
zis[streamId].removeUnderlying();
zis[streamId].flushUnderlying();
zis[streamId].setUnderlying(NULL, 0);
delete ms;
bufptr = netbuf;

3
common/rfb/zrleDecode.h
View File

@ -174,7 +174,8 @@ void ZRLE_DECODE (const Rect& r, rdr::InStream* is,
}
}
zis->removeUnderlying();
zis->flushUnderlying();
zis->setUnderlying(NULL, 0);
}
#undef ZRLE_DECODE