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Type:
Bug
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Resolution: Unresolved
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Priority:
Minor - P4
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None
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Affects Version/s: None
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Component/s: None
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Labels:
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Query Optimization
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ALL
When used to parse a field with the name maxTimeMSOpOnly, parseMaxTimeMS increases the max permitted value beyond INT_MAX.
However, the returned value is of type int - the result will be narrowed long long -> int.
StatusWith<int> parseMaxTimeMS(BSONElement maxTimeMSElt) {
...
const long long maxVal = maxTimeMSElt.fieldNameStringData() == kMaxTimeMSOpOnlyField
? (long long)(INT_MAX) + kMaxTimeMSOpOnlyMaxPadding
: INT_MAX;
...
if (maxTimeMSLongLong < 0 || maxTimeMSLongLong > maxVal)
return Status(ErrorCodes::BadValue, ...);
..
return StatusWith<int>(static_cast<int>(maxTimeMSLongLong));
}
The justification for this leeway:
src/mongo/db/query/max_time_ms_parser.h
// A constant by which 'maxTimeMSOpOnly' values are allowed to exceed the max allowed value for // 'maxTimeMS'. This is because mongod and mongos server processes add a small amount to the // 'maxTimeMS' value they are given before passing it on as 'maxTimeMSOpOnly', to allow for // clock precision. static constexpr auto kMaxTimeMSOpOnlyMaxPadding = 100LL;
Given this, if maxTimeMS is provided INT_MAX, any maxTimeMSOpOnly derived from increasing this value slightly will be parsed as a very negative int value.
The only use of this method on a field named maxTimeMSOpOnly identified so far is:
src/mongo/db/service_entry_point_common.cpp
void ExecCommandDatabase::_initiateCommand() {
...
const auto maxTimeMS =
Milliseconds{uassertStatusOK(parseMaxTimeMS(cmdOptionMaxTimeMSField))};
const auto maxTimeMSOpOnly =
Milliseconds{uassertStatusOK(parseMaxTimeMS(maxTimeMSOpOnlyField))};
if ((maxTimeMS > Milliseconds::zero() || maxTimeMSOpOnly > Milliseconds::zero()) &&
command->getLogicalOp() != LogicalOp::opGetMore) {
...
if (!ignoreMaxTimeMSOpOnly && maxTimeMSOpOnly > Milliseconds::zero() &&
(maxTimeMS == Milliseconds::zero() || maxTimeMSOpOnly < maxTimeMS)) {
opCtx->storeMaxTimeMS(maxTimeMS);
opCtx->setDeadlineByDate(startedCommandExecAt + maxTimeMSOpOnly,
ErrorCodes::MaxTimeMSExpired);
} else if (maxTimeMS > Milliseconds::zero()) {
opCtx->setDeadlineByDate(startedCommandExecAt + maxTimeMS,
ErrorCodes::MaxTimeMSExpired);
}
}
This compares > 0, so may treat this situation as if maxTimeMSOpOnly were 0 or unset.
Given INT_MAX milliseconds is around 25 days, it's possible this has no real-world impact.