https://github.com/llvmbot created
https://github.com/llvm/llvm-project/pull/155712
Backport 6291b63a9a104fe93f8e4e279ef2237dc081304f
Requested by: @var-const
>From d524d0397cc437f6f280606837177020fb41427a Mon Sep 17 00:00:00 2001
From: Louis Dionne <ldionn...@gmail.com>
Date: Tue, 15 Jul 2025 10:40:54 -0400
Subject: [PATCH] [libc++] Ensure that we restore invariants in
basic_filebuf::overflow (#147389)
In rare circumstances, the invariants could fail to be restored.
(cherry picked from commit 6291b63a9a104fe93f8e4e279ef2237dc081304f)
---
libcxx/include/fstream | 35 ++++++---
.../overflow.writefail.pass.cpp | 72 +++++++++++++++++++
2 files changed, 96 insertions(+), 11 deletions(-)
create mode 100644
libcxx/test/std/input.output/file.streams/fstreams/filebuf.virtuals/overflow.writefail.pass.cpp
diff --git a/libcxx/include/fstream b/libcxx/include/fstream
index c86f709bedb80..dc5c47304f014 100644
--- a/libcxx/include/fstream
+++ b/libcxx/include/fstream
@@ -821,6 +821,14 @@ typename basic_filebuf<_CharT, _Traits>::int_type
basic_filebuf<_CharT, _Traits>
template <class _CharT, class _Traits>
typename basic_filebuf<_CharT, _Traits>::int_type basic_filebuf<_CharT,
_Traits>::overflow(int_type __c) {
+ auto __failed = [this]() {
+ if (this->pptr() == this->epptr() + 1) {
+ this->pbump(-1); // lose the character we overflowed above -- we don't
really have a
+ // choice since we couldn't commit the contents of the
put area
+ }
+ return traits_type::eof();
+ };
+
if (__file_ == nullptr)
return traits_type::eof();
__write_mode();
@@ -841,8 +849,9 @@ typename basic_filebuf<_CharT, _Traits>::int_type
basic_filebuf<_CharT, _Traits>
if (__always_noconv_) {
size_t __n = static_cast<size_t>(this->pptr() - this->pbase());
- if (std::fwrite(this->pbase(), sizeof(char_type), __n, __file_) != __n)
- return traits_type::eof();
+ if (std::fwrite(this->pbase(), sizeof(char_type), __n, __file_) != __n) {
+ return __failed();
+ }
} else {
if (!__cv_)
std::__throw_bad_cast();
@@ -854,34 +863,38 @@ typename basic_filebuf<_CharT, _Traits>::int_type
basic_filebuf<_CharT, _Traits>
char* __extbuf_end = __extbuf_;
do {
codecvt_base::result __r = __cv_->out(__st_, __b, __p, __end, __extbuf_,
__extbuf_ + __ebs_, __extbuf_end);
- if (__end == __b)
- return traits_type::eof();
+ if (__end == __b) {
+ return __failed();
+ }
// No conversion needed: output characters directly to the file, done.
if (__r == codecvt_base::noconv) {
size_t __n = static_cast<size_t>(__p - __b);
- if (std::fwrite(__b, 1, __n, __file_) != __n)
- return traits_type::eof();
+ if (std::fwrite(__b, 1, __n, __file_) != __n) {
+ return __failed();
+ }
break;
// Conversion successful: output the converted characters to the file,
done.
} else if (__r == codecvt_base::ok) {
size_t __n = static_cast<size_t>(__extbuf_end - __extbuf_);
- if (std::fwrite(__extbuf_, 1, __n, __file_) != __n)
- return traits_type::eof();
+ if (std::fwrite(__extbuf_, 1, __n, __file_) != __n) {
+ return __failed();
+ }
break;
// Conversion partially successful: output converted characters to the
file and repeat with the
// remaining characters.
} else if (__r == codecvt_base::partial) {
size_t __n = static_cast<size_t>(__extbuf_end - __extbuf_);
- if (std::fwrite(__extbuf_, 1, __n, __file_) != __n)
- return traits_type::eof();
+ if (std::fwrite(__extbuf_, 1, __n, __file_) != __n) {
+ return __failed();
+ }
__b = const_cast<char_type*>(__end);
continue;
} else {
- return traits_type::eof();
+ return __failed();
}
} while (true);
}
diff --git
a/libcxx/test/std/input.output/file.streams/fstreams/filebuf.virtuals/overflow.writefail.pass.cpp
b/libcxx/test/std/input.output/file.streams/fstreams/filebuf.virtuals/overflow.writefail.pass.cpp
new file mode 100644
index 0000000000000..27e06982d749b
--- /dev/null
+++
b/libcxx/test/std/input.output/file.streams/fstreams/filebuf.virtuals/overflow.writefail.pass.cpp
@@ -0,0 +1,72 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: no-filesystem
+
+// setrlimit(RLIMIT_FSIZE) seems to only work as intended on Apple platforms
+// REQUIRES: target={{.+}}-apple-{{.+}}
+
+// <fstream>
+
+// Make sure that we properly handle the case where we try to write content to
a file
+// but we fail to do so because std::fwrite fails.
+
+#include <cassert>
+#include <csignal>
+#include <cstddef>
+#include <fstream>
+#include <string>
+
+#include "platform_support.h"
+#include "test_macros.h"
+
+#if __has_include(<sys/resource.h>)
+# include <sys/resource.h>
+void limit_file_size_to(std::size_t bytes) {
+ rlimit lim = {bytes, bytes};
+ assert(setrlimit(RLIMIT_FSIZE, &lim) == 0);
+
+ std::signal(SIGXFSZ, [](int) {}); // ignore SIGXFSZ to ensure std::fwrite
fails
+}
+#else
+# error No known way to limit the amount of filesystem space available
+#endif
+
+template <class CharT>
+void test() {
+ std::string temp = get_temp_file_name();
+ std::basic_filebuf<CharT> fbuf;
+ assert(fbuf.open(temp, std::ios::out | std::ios::trunc));
+
+ std::size_t const limit = 100000;
+ limit_file_size_to(limit);
+
+ std::basic_string<CharT> large_block(limit / 10, CharT(42));
+
+ std::streamsize ret;
+ std::size_t bytes_written = 0;
+ while ((ret = fbuf.sputn(large_block.data(), large_block.size())) != 0) {
+ bytes_written += ret;
+
+ // In theory, it's possible for an implementation to allow writing
arbitrarily more bytes than
+ // set by setrlimit, but in practice if we bust 100x our limit, something
else is wrong with the
+ // test and we'd end up looping forever.
+ assert(bytes_written < 100 * limit);
+ }
+
+ fbuf.close();
+}
+
+int main(int, char**) {
+ test<char>();
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+ test<wchar_t>();
+#endif
+
+ return 0;
+}
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