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Merge #18383: refactor: Check for overflow when calculating sum of tx outputs

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f65c9ad40f2f5cdc581bdaf72e7dc68e9d7f7a80 Check for overflow when calculating sum of outputs (Elichai Turkel)

Pull request description:

  This was reported by practicalswift here #18046
  The exact order of the if, is important, we first do `!MoneyRange(tx_out.nValue)` to make sure the amount is non-negative. and then `std::numeric_limits<CAmount>::max() - tx_out.nValue < nValueOut` checks that the addition cannot overflow (if we won't check that the amount is positive this check can also overflow! (by doing something like `max - -max`))
  and only then we make sure that the some is also valid `!MoneyRange(nValueOut + tx_out.nValue)`
  if any of these conditions fail we throw.

  the overflowing logic:
  ```
  a + b > max // we want to fail if a+b is more than the maximum -> will overflow
  b > max - a
  max - a < b
  ```

  Closes: #18046

ACKs for top commit:
  MarcoFalke:
    ACK f65c9ad40f2f5cdc581bdaf72e7dc68e9d7f7a80, checked that clang with O2 produces identical binaries 💕
  practicalswift:
    ACK f65c9ad40f2f5cdc581bdaf72e7dc68e9d7f7a80
  instagibbs:
    utACK f65c9ad40f
  vasild:
    ACK f65c9ad40f2f5cdc581bdaf72e7dc68e9d7f7a80 modulo `s/assert.h/cassert/`

Tree-SHA512: 512d6cf4762f24c41cf9a38da486b17b19c634fa3f4efbdebfe6608779e96fc3014d5d2d29adb8001e113152c0217bbd5b3900ac4edc7b8abe77f82f36209e33
This commit is contained in:
MarcoFalke 2020-04-03 06:50:10 +08:00 committed by pasta
parent 4f632952bf
commit c542cd3a98
1 changed files with 5 additions and 2 deletions
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7
src/primitives/transaction.cpp
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@ -9,6 +9,8 @@
#include <tinyformat.h>
#include <util/strencodings.h>
#include <assert.h>
std::string COutPoint::ToString() const
{
return strprintf("COutPoint(%s, %u)", hash.ToString()/*.substr(0,10)*/, n);
@ -99,10 +101,11 @@ CAmount CTransaction::GetValueOut() const
{
CAmount nValueOut = 0;
for (const auto& tx_out : vout) {
nValueOut += tx_out.nValue;
if (!MoneyRange(tx_out.nValue) || !MoneyRange(nValueOut))
if (!MoneyRange(tx_out.nValue) || !MoneyRange(nValueOut + tx_out.nValue))
throw std::runtime_error(std::string(__func__) + ": value out of range");
nValueOut += tx_out.nValue;
}
assert(MoneyRange(nValueOut));
return nValueOut;
}