From 2a2bd96d0d2109384a0eedde843ba811d2e18738 Mon Sep 17 00:00:00 2001
From: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Date: Thu, 6 Feb 2025 14:24:17 +0000
Subject: [PATCH] libstdc++: fix a dangling reference crash in
ranges::is_permutation [PR118160]
The code was caching the result of `invoke(proj, *it)` in a local
`auto &&` variable. The problem is that this may create dangling
references, for instance in case `proj` is `std::identity` (the common
case) and `*it` produces a prvalue: lifetime extension does not
apply here due to the expressions involved.
Instead, store (and lifetime-extend) the result of `*it` in a separate
variable, then project that variable. While at it, also forward the
result of the projection to the predicate, so that the predicate can
act on the proper value category.
libstdc++-v3/ChangeLog:
PR libstdc++/118160
PR libstdc++/100249
* include/bits/ranges_algo.h (__is_permutation_fn): Avoid a
dangling reference by storing the result of the iterator
dereference and the result of the projection in two distinct
variables, in order to lifetime-extend each one.
Forward the projected value to the predicate.
* testsuite/25_algorithms/is_permutation/constrained.cc: Add a
test with a range returning prvalues. Test it in a constexpr
context, in order to rely on the compiler to catch UB.
Signed-off-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
---
libstdc++-v3/include/bits/ranges_algo.h | 7 +++++--
.../25_algorithms/is_permutation/constrained.cc | 13 +++++++++++++
2 files changed, 18 insertions(+), 2 deletions(-)
diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h
index df92598f51a1..a72eab582be0 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -567,9 +567,12 @@ namespace ranges
for (auto __scan = __first1; __scan != __last1; ++__scan)
{
- auto&& __proj_scan = std::__invoke(__proj1, *__scan);
+ auto&& __scan_deref = *__scan;
+ auto&& __proj_scan =
+ std::__invoke(__proj1, std::forward<decltype(__scan_deref)>(__scan_deref));
auto __comp_scan = [&] <typename _Tp> (_Tp&& __arg) -> bool {
- return std::__invoke(__pred, __proj_scan,
+ return std::__invoke(__pred,
+ std::forward<decltype(__proj_scan)>(__proj_scan),
std::forward<_Tp>(__arg));
};
if (__scan != ranges::find_if(__first1, __scan,
diff --git a/libstdc++-v3/testsuite/25_algorithms/is_permutation/constrained.cc b/libstdc++-v3/testsuite/25_algorithms/is_permutation/constrained.cc
index cd4b3fe8c32f..c96d7c568ead 100644
--- a/libstdc++-v3/testsuite/25_algorithms/is_permutation/constrained.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/is_permutation/constrained.cc
@@ -19,6 +19,7 @@
#include <algorithm>
#include <iterator>
+#include <ranges>
#include <testsuite_hooks.h>
#include <testsuite_iterators.h>
@@ -76,10 +77,22 @@ test03()
while (std::next_permutation(std::begin(cx), std::end(cx)));
}
+constexpr
+bool
+test04() // PR118160, do not create dangling references
+{
+ int x[] = { 4, 3, 2, 1 };
+ auto y = std::views::iota(1, 5);
+ return ranges::is_permutation(x, y) && ranges::is_permutation(y, x);
+}
+
+static_assert(test04());
+
int
main()
{
test01();
test02();
test03();
+ VERIFY( test04() );
}
--
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