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The cartesian_apply() function in TestQuiesceDb.cc had a stack-use-
after-scope issue detected by ASan. The problem was that the lambda
function at line 513 had an implicit return type deduction that
returned a value instead of a reference:
auto f = [&q](const auto &args) {
q = div(q.quot, args.size());
return args.at(q.rem); // Returns V instead of V const&
};
Even though args.at(q.rem) returns a const reference to an element
in the array, the lambda's auto return type deduction caused it to
return by value. This meant the tuple at line 518:
auto apply_tuple = std::tuple<V const &...> { f(array_args)... };
was storing references to temporary values that went out of scope
immediately after tuple construction. When std::apply() later tried
to use these references, it accessed freed stack memory.
Fix by explicitly specifying the lambda's return type as decltype(auto)
to preserve the reference semantics:
auto f = [&q](const auto &args) -> decltype(auto) {
q = div(q.quot, args.size());
return args.at(q.rem); // Now returns V const& as intended
};
This ensures the lambda returns a reference to the array element,
which remains valid for the lifetime of array_args (the entire scope
of cartesian_apply()). This preserves the original optimization of
avoiding copies while fixing the use-after-scope issue.
Signed-off-by: Kefu Chai <k.chai@proxmox.com>
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Author
|
the failure is observed when testing with ASan enabled: |
Contributor
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|
@athanatos hi Sam, could you help review this change? |
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jenkins test make check |
1 similar comment
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jenkins test make check |
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@batrick hi Patrick, could you help review this change? |
batrick
approved these changes
Jan 28, 2026
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Thanks! |
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The
cartesian_apply()function inTestQuiesceDb.cchad a stack-use- after-scope issue detected by ASan. The problem was that the lambda function at line 513 had an implicit return type deduction that returned a value instead of a reference:Even though
args.at(q.rem)returns a const reference to an element in the array, the lambda's auto return type deduction caused it to return by value. This meant the tuple at line 518:was storing references to temporary values that went out of scope immediately after tuple construction. When
std::apply()later tried to use these references, it accessed freed stack memory.Fix by explicitly specifying the lambda's return type as
decltype(auto)to preserve the reference semantics:This ensures the lambda returns a reference to the array element, which remains valid for the lifetime of
array_args(the entire scope ofcartesian_apply()). This preserves the original optimization of avoiding copies while fixing the use-after-scope issue.Contribution Guidelines
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