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Allocate more space if necessary in RandSeedAddPerfMon

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Currently we use a fixed buffer of 250000 bytes to request
HKEY_PERFORMANCE_DATA. In many cases this is not enough, causing the
entropy collection to be skipped.

Use a loop that grows the buffer as specified in the RegQueryValueEx
documentation:
http://msdn.microsoft.com/en-us/library/windows/desktop/ms724911%28v=vs.85%29.aspx

(as the size of the performance data can differ for every call, the
normal solution of requesting the size then allocating that can't work)
This commit is contained in:
Wladimir J. van der Laan 2014-06-24 15:27:37 +02:00
parent be873f6454
commit 8ae973c00c
1 changed files with 11 additions and 2 deletions
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13
src/util.cpp
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@ -169,8 +169,17 @@ void RandAddSeedPerfmon()
// Don't need this on Linux, OpenSSL automatically uses /dev/urandom
// Seed with the entire set of perfmon data
std::vector <unsigned char> vData(250000,0);
unsigned long nSize = vData.size();
long ret = RegQueryValueExA(HKEY_PERFORMANCE_DATA, "Global", NULL, NULL, begin_ptr(vData), &nSize);
long ret = 0;
unsigned long nSize = 0;
const size_t nMaxSize = 10000000; // Bail out at more than 10MB of performance data
while (true)
{
nSize = vData.size();
ret = RegQueryValueExA(HKEY_PERFORMANCE_DATA, "Global", NULL, NULL, begin_ptr(vData), &nSize);
if (ret != ERROR_MORE_DATA || vData.size() >= nMaxSize)
break;
vData.resize(std::max((vData.size()*3)/2, nMaxSize)); // Grow size of buffer exponentially
}
RegCloseKey(HKEY_PERFORMANCE_DATA);
if (ret == ERROR_SUCCESS)
{