From 5dba17a3e709859968f939354e6e5e8d796012d3 Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Thu, 9 Oct 2025 11:09:34 +0100 Subject: [PATCH] libstdc++: Avoid overflow in timeout conversions [PR113327] MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When converting from a coarse duration with a very large value, the existing code scales that up to chrono::seconds which overflows the chrono::seconds::rep type. For example, sleep_for(chrono::hours::max()) tries to calculate LLONG_MAX * 3600, which overflows to -3600 and so the sleep returns immediately. The solution in this commit is inspired by this_thread::sleep_for in libc++ which compares the duration argument to chrono::duration(nanoseconds::max()) and limits the duration to nanoseconds::max(). Because we split the duration into seconds and nanoseconds, we can use seconds::max() as our upper limit. We might need to limit further if seconds::max() doesn't fit in the type used for sleeping, which is one of std::time_t, unsigned int, or chrono::milliseconds. To fix this everywhere that uses timeouts, new functions are introduced for converting from a chrono::duration or chrono::time_point to a timespec (or __gthread_time_t which is just a timespec on Linux). These functions provide one central place where we can avoid overflow and also handle negative timeouts (as these produce errors when passed to OS functions that do not accept absolute times before the epoch). All negative durations are converted to zero, and negative time_points are converted to the epoch. The new __to_timeout_gthread_time_t function in requires adding to that header, but that only affects . All other consumers of were already including for timeouts (e.g. and ). libstdc++-v3/ChangeLog: PR libstdc++/113327 PR libstdc++/116586 PR libstdc++/119258 PR libstdc++/58931 * include/bits/chrono.h (__to_timeout_timespec): New overloaded function templates for converting chrono types to timespec. * include/bits/std_mutex.h (__to_timeout_gthread_time_t): New function template for converting time_point to __gthread_time_t. * include/bits/this_thread_sleep.h (sleep_for): Use __to_timeout_timespec. (__sleep_for): Remove namespace-scope declaration. * include/std/condition_variable: Likewise. * include/std/mutex: Likewise. * include/std/shared_mutex: Likewise. * src/c++11/thread.cc (limit): New helper function. (__sleep_for): Use limit to prevent overflow when converting chrono::seconds to time_t, unsigned, or chrono::milliseconds. * src/c++20/atomic.cc: Use __to_timeout_timespec and __to_timeout_gthread_time_t for timeouts. * testsuite/30_threads/this_thread/113327.cc: New test. Reviewed-by: Mike Crowe Reviewed-by: Tomasz Kamiński --- libstdc++-v3/include/bits/chrono.h | 72 +++++++++++++++++++ libstdc++-v3/include/bits/std_mutex.h | 26 ++++++- libstdc++-v3/include/bits/this_thread_sleep.h | 20 ++---- libstdc++-v3/include/std/condition_variable | 20 +----- libstdc++-v3/include/std/mutex | 18 +---- libstdc++-v3/include/std/shared_mutex | 39 ++-------- libstdc++-v3/src/c++11/thread.cc | 48 +++++++++++-- libstdc++-v3/src/c++20/atomic.cc | 18 +---- .../30_threads/this_thread/113327.cc | 29 ++++++++ 9 files changed, 186 insertions(+), 104 deletions(-) create mode 100644 libstdc++-v3/testsuite/30_threads/this_thread/113327.cc diff --git a/libstdc++-v3/include/bits/chrono.h b/libstdc++-v3/include/bits/chrono.h index 8de8e756c714..7f505aa0f0ff 100644 --- a/libstdc++-v3/include/bits/chrono.h +++ b/libstdc++-v3/include/bits/chrono.h @@ -1515,6 +1515,78 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2) } // namespace filesystem #endif // C++17 && HOSTED +#if defined _GLIBCXX_USE_NANOSLEEP || defined _GLIBCXX_USE_CLOCK_REALTIME \ + || defined _GLIBCXX_HAS_GTHREADS +namespace chrono +{ +/// @cond undocumented + +#pragma GCC diagnostic push +#pragma GCC diagnostic ignored "-Wc++17-extensions" + // Convert a chrono::duration to a relative time represented as timespec + // (e.g. for use with nanosleep). + template + [[__nodiscard__]] _GLIBCXX14_CONSTEXPR inline + struct ::timespec + __to_timeout_timespec(const duration<_Rep, _Period>& __d) + { + struct ::timespec __ts{}; + + if (__d < __d.zero()) // Negative timeouts don't make sense. + return __ts; + + if constexpr (ratio_greater<_Period, ratio<1>>::value + || treat_as_floating_point<_Rep>::value) + { + // Converting from e.g. chrono::hours::max() to chrono::seconds + // would evaluate LLONG_MAX * 3600 which would overflow. + // Limit to chrono::seconds::max(). + chrono::duration __fmax(chrono::seconds::max()); + if (__d > __fmax) [[__unlikely__]] + return chrono::__to_timeout_timespec(chrono::seconds::max()); + } + + auto __s = chrono::duration_cast(__d); + + if constexpr (is_integral::value) // POSIX.1-2001 allows floating + { + // Also limit to time_t maximum (only relevant for 32-bit time_t). + constexpr auto __tmax = numeric_limits::max(); + if (__s.count() > __tmax) [[__unlikely__]] + { + __ts.tv_sec = __tmax; + return __ts; + } + } + + auto __ns = chrono::duration_cast(__d - __s); + + if constexpr (treat_as_floating_point<_Rep>::value) + if (__ns.count() > 999999999) [[__unlikely__]] + __ns = chrono::nanoseconds(999999999); + + __ts.tv_sec = static_cast(__s.count()); + __ts.tv_nsec = static_cast(__ns.count()); + return __ts; + } +#pragma GCC diagnostic pop + + // Convert a chrono::time_point to an absolute time represented as timespec. + // All times before the epoch get converted to the epoch, so this assumes + // that we only use it for clocks where that's true. + // It should be safe to use this for system_clock and steady_clock. + template + [[__nodiscard__]] _GLIBCXX14_CONSTEXPR inline + struct ::timespec + __to_timeout_timespec(const time_point<_Clock, _Dur>& __t) + { + return chrono::__to_timeout_timespec(__t.time_since_epoch()); + } + +/// @endcond +} // namespace chrono +#endif // USE_NANOSLEEP || USE_CLOCK_REALTIME || HAS_GTHREADS + _GLIBCXX_END_NAMESPACE_VERSION } // namespace std diff --git a/libstdc++-v3/include/bits/std_mutex.h b/libstdc++-v3/include/bits/std_mutex.h index 777097b00a46..5f9f1544587c 100644 --- a/libstdc++-v3/include/bits/std_mutex.h +++ b/libstdc++-v3/include/bits/std_mutex.h @@ -39,6 +39,7 @@ #else #include // EBUSY +#include #include #include @@ -210,8 +211,31 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION __gthread_cond_t _M_cond; #endif }; - /// @endcond +namespace chrono +{ +#pragma GCC diagnostic push +#pragma GCC diagnostic ignored "-Wc++17-extensions" + // Convert a time_point to an absolute time represented as __gthread_time_t + // (which is typically just a typedef for struct timespec). + template + [[__nodiscard__]] _GLIBCXX14_CONSTEXPR inline + __gthread_time_t + __to_timeout_gthread_time_t(const time_point<_Clock, _Dur>& __t) + { + auto __ts = chrono::__to_timeout_timespec(__t.time_since_epoch()); + if constexpr (is_same<::timespec, __gthread_time_t>::value) + return __ts; + else if constexpr (is_convertible<::timespec, __gthread_time_t>::value) + return __ts; + else if constexpr (is_scalar<__gthread_time_t>::value) // Assume seconds: + return static_cast<__gthread_time_t>(__ts.tv_sec); + else // Assume this works and the members are in the correct order: + return __gthread_time_t{ __ts.tv_sec, __ts.tv_nsec }; + } +#pragma GCC diagnostic pop +} + /// @endcond #endif // _GLIBCXX_HAS_GTHREADS /// Do not acquire ownership of the mutex. diff --git a/libstdc++-v3/include/bits/this_thread_sleep.h b/libstdc++-v3/include/bits/this_thread_sleep.h index 57f89f858952..01f25dda2af0 100644 --- a/libstdc++-v3/include/bits/this_thread_sleep.h +++ b/libstdc++-v3/include/bits/this_thread_sleep.h @@ -36,6 +36,7 @@ #if __cplusplus >= 201103L #include // std::chrono::* +#include // __int_traits #ifdef _GLIBCXX_USE_NANOSLEEP # include // errno, EINTR @@ -59,11 +60,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { #ifndef _GLIBCXX_NO_SLEEP -#ifndef _GLIBCXX_USE_NANOSLEEP - void - __sleep_for(chrono::seconds, chrono::nanoseconds); -#endif - /// this_thread::sleep_for template inline void @@ -71,18 +67,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { if (__rtime <= __rtime.zero()) return; - auto __s = chrono::duration_cast(__rtime); - auto __ns = chrono::duration_cast(__rtime - __s); + + struct timespec __ts = chrono::__to_timeout_timespec(__rtime); #ifdef _GLIBCXX_USE_NANOSLEEP - struct ::timespec __ts = - { - static_cast(__s.count()), - static_cast(__ns.count()) - }; while (::nanosleep(&__ts, &__ts) == -1 && errno == EINTR) { } #else - __sleep_for(__s, __ns); + using chrono::seconds; + using chrono::nanoseconds; + void __sleep_for(seconds __s, nanoseconds __ns); + __sleep_for(seconds(__ts.tv_sec), nanoseconds(__ts.tv_nsec)); #endif } diff --git a/libstdc++-v3/include/std/condition_variable b/libstdc++-v3/include/std/condition_variable index 3525ff35ba31..dcf0b9235cf3 100644 --- a/libstdc++-v3/include/std/condition_variable +++ b/libstdc++-v3/include/std/condition_variable @@ -193,15 +193,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION __wait_until_impl(unique_lock& __lock, const chrono::time_point& __atime) { - auto __s = chrono::time_point_cast(__atime); - auto __ns = chrono::duration_cast(__atime - __s); - - __gthread_time_t __ts = - { - static_cast(__s.time_since_epoch().count()), - static_cast(__ns.count()) - }; - + __gthread_time_t __ts = chrono::__to_timeout_gthread_time_t(__atime); _M_cond.wait_until(*__lock.mutex(), CLOCK_MONOTONIC, __ts); return (steady_clock::now() < __atime @@ -214,15 +206,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION __wait_until_impl(unique_lock& __lock, const chrono::time_point& __atime) { - auto __s = chrono::time_point_cast(__atime); - auto __ns = chrono::duration_cast(__atime - __s); - - __gthread_time_t __ts = - { - static_cast(__s.time_since_epoch().count()), - static_cast(__ns.count()) - }; - + __gthread_time_t __ts = chrono::__to_timeout_gthread_time_t(__atime); _M_cond.wait_until(*__lock.mutex(), __ts); return (system_clock::now() < __atime diff --git a/libstdc++-v3/include/std/mutex b/libstdc++-v3/include/std/mutex index 631c38069d4a..d4fc4c646488 100644 --- a/libstdc++-v3/include/std/mutex +++ b/libstdc++-v3/include/std/mutex @@ -179,14 +179,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _M_try_lock_until(const chrono::time_point& __atime) { - auto __s = chrono::time_point_cast(__atime); - auto __ns = chrono::duration_cast(__atime - __s); - - __gthread_time_t __ts = { - static_cast(__s.time_since_epoch().count()), - static_cast(__ns.count()) - }; - + __gthread_time_t __ts = chrono::__to_timeout_gthread_time_t(__atime); return static_cast<_Derived*>(this)->_M_timedlock(__ts); } @@ -196,14 +189,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _M_try_lock_until(const chrono::time_point& __atime) { - auto __s = chrono::time_point_cast(__atime); - auto __ns = chrono::duration_cast(__atime - __s); - - __gthread_time_t __ts = { - static_cast(__s.time_since_epoch().count()), - static_cast(__ns.count()) - }; - + __gthread_time_t __ts = chrono::__to_timeout_gthread_time_t(__atime); return static_cast<_Derived*>(this)->_M_clocklock(CLOCK_MONOTONIC, __ts); } diff --git a/libstdc++-v3/include/std/shared_mutex b/libstdc++-v3/include/std/shared_mutex index 94c8532399d9..a267ad7c4f66 100644 --- a/libstdc++-v3/include/std/shared_mutex +++ b/libstdc++-v3/include/std/shared_mutex @@ -520,15 +520,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION try_lock_until(const chrono::time_point& __atime) { - auto __s = chrono::time_point_cast(__atime); - auto __ns = chrono::duration_cast(__atime - __s); - - __gthread_time_t __ts = - { - static_cast(__s.time_since_epoch().count()), - static_cast(__ns.count()) - }; - + struct timespec __ts = chrono::__to_timeout_timespec(__atime); int __ret = __glibcxx_rwlock_timedwrlock(&_M_rwlock, &__ts); // On self-deadlock, we just fail to acquire the lock. Technically, // the program violated the precondition. @@ -546,15 +538,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION try_lock_until(const chrono::time_point& __atime) { - auto __s = chrono::time_point_cast(__atime); - auto __ns = chrono::duration_cast(__atime - __s); - - __gthread_time_t __ts = - { - static_cast(__s.time_since_epoch().count()), - static_cast(__ns.count()) - }; - + struct timespec __ts = chrono::__to_timeout_timespec(__atime); int __ret = pthread_rwlock_clockwrlock(&_M_rwlock, CLOCK_MONOTONIC, &__ts); // On self-deadlock, we just fail to acquire the lock. Technically, @@ -596,14 +580,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION try_lock_shared_until(const chrono::time_point& __atime) { - auto __s = chrono::time_point_cast(__atime); - auto __ns = chrono::duration_cast(__atime - __s); - - __gthread_time_t __ts = - { - static_cast(__s.time_since_epoch().count()), - static_cast(__ns.count()) - }; + struct timespec __ts = chrono::__to_timeout_timespec(__atime); int __ret; // Unlike for lock(), we are not allowed to throw an exception so if @@ -636,15 +613,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION try_lock_shared_until(const chrono::time_point& __atime) { - auto __s = chrono::time_point_cast(__atime); - auto __ns = chrono::duration_cast(__atime - __s); - - __gthread_time_t __ts = - { - static_cast(__s.time_since_epoch().count()), - static_cast(__ns.count()) - }; - + struct timespec __ts = chrono::__to_timeout_timespec(__atime); int __ret = pthread_rwlock_clockrdlock(&_M_rwlock, CLOCK_MONOTONIC, &__ts); // On self-deadlock, we just fail to acquire the lock. Technically, diff --git a/libstdc++-v3/src/c++11/thread.cc b/libstdc++-v3/src/c++11/thread.cc index 6c2ec2978f88..5cfe56453af6 100644 --- a/libstdc++-v3/src/c++11/thread.cc +++ b/libstdc++-v3/src/c++11/thread.cc @@ -231,10 +231,30 @@ namespace std _GLIBCXX_VISIBILITY(default) _GLIBCXX_BEGIN_NAMESPACE_VERSION namespace this_thread { +namespace +{ + // returns min(s, Dur::max()) + template + inline chrono::seconds + limit(chrono::seconds s) + { + static_assert(ratio_equal>::value, + "period must be seconds to avoid potential overflow"); + + if (s > Dur::max()) [[__unlikely__]] + s = chrono::duration_cast(Dur::max()); + return s; + } +} + void __sleep_for(chrono::seconds __s, chrono::nanoseconds __ns) { #ifdef _GLIBCXX_USE_NANOSLEEP +#pragma GCC diagnostic ignored "-Wc++17-extensions" + if constexpr (is_integral::value) // POSIX.1-2001 allows floating + __s = limit>(__s); + struct ::timespec __ts = { static_cast(__s.count()), @@ -246,6 +266,8 @@ namespace this_thread const auto target = chrono::steady_clock::now() + __s + __ns; while (true) { + __s = limit>(__s); + unsigned secs = __s.count(); if (__ns.count() > 0) { @@ -271,12 +293,28 @@ namespace this_thread break; __s = chrono::duration_cast(target - now); __ns = chrono::duration_cast(target - (now + __s)); - } + } #elif defined(_GLIBCXX_USE_WIN32_SLEEP) - unsigned long ms = __ns.count() / 1000000; - if (__ns.count() > 0 && ms == 0) - ms = 1; - ::Sleep(chrono::milliseconds(__s).count() + ms); + + // Can't use limit(__s) here because it would + // multiply __s by 1000 which could overflow. + // Limit to milliseconds::max() and truncate to seconds: + chrono::milliseconds ms = chrono::milliseconds::max(); + if (__s < chrono::duration_cast(ms)) + { + ms = __s; + ms += chrono::__detail::ceil(__ns); + } + + // Use Sleep(DWORD millis) where DWORD is uint32_t. + constexpr chrono::milliseconds max_sleep(INFINITE - 1u); + while (ms > max_sleep) + { + ::Sleep(max_sleep.count()); + ms -= max_sleep; + } + + ::Sleep(ms.count()); #endif } } diff --git a/libstdc++-v3/src/c++20/atomic.cc b/libstdc++-v3/src/c++20/atomic.cc index 4120e1a0817f..7978809cd223 100644 --- a/libstdc++-v3/src/c++20/atomic.cc +++ b/libstdc++-v3/src/c++20/atomic.cc @@ -350,14 +350,7 @@ __platform_wait_until(const __platform_wait_t* __addr, __platform_wait_t __old, const __wait_clock_t::time_point& __atime) noexcept { - auto __s = chrono::time_point_cast(__atime); - auto __ns = chrono::duration_cast(__atime - __s); - - struct timespec __rt = - { - static_cast(__s.time_since_epoch().count()), - static_cast(__ns.count()) - }; + struct timespec __rt = chrono::__to_timeout_timespec(__atime); if (syscall (SYS_futex, __addr, static_cast(__futex_wait_flags::__wait_bitset_private), @@ -378,14 +371,7 @@ bool __cond_wait_until(__condvar& __cv, mutex& __mx, const __wait_clock_t::time_point& __atime) { - auto __s = chrono::time_point_cast(__atime); - auto __ns = chrono::duration_cast(__atime - __s); - - __gthread_time_t __ts = - { - static_cast(__s.time_since_epoch().count()), - static_cast(__ns.count()) - }; + __gthread_time_t __ts = chrono::__to_timeout_gthread_time_t(__atime); #ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT if constexpr (is_same_v) diff --git a/libstdc++-v3/testsuite/30_threads/this_thread/113327.cc b/libstdc++-v3/testsuite/30_threads/this_thread/113327.cc new file mode 100644 index 000000000000..2daa2b0e46e2 --- /dev/null +++ b/libstdc++-v3/testsuite/30_threads/this_thread/113327.cc @@ -0,0 +1,29 @@ +// { dg-do run { target c++11 } } +// { dg-additional-options "-pthread" { target pthread } } +// { dg-require-gthreads "" } + +// PR libstdc++/113327 +// std::sleep_for(std::chrono::hours::max()) returns immediately + +#include +#include +#include +#include + +int main() +{ + std::thread sleepy([] { + // Rather than overflowing to a negative value, the timeout should be + // truncated to seconds::max() and so sleep for 292 billion years. + std::this_thread::sleep_for(std::chrono::minutes::max()); + // This should not happen: + throw 1; + }); + // Give the new thread a chance to start sleeping: + std::this_thread::yield(); + std::this_thread::sleep_for(std::chrono::seconds(2)); + // If we get here without the other thread throwing an exception + // then it should be sleeping peacefully, so the test passed. + // pthread_kill(sleepy.native_handle(), SIGINT); + std::_Exit(0); +}