coffee/fmt
1
0
Fork 0
mirror of https://github.com/fmtlib/fmt.git synced 2026-11-09 14:50:24 +08:00
Code Issues Packages Projects Releases Wiki Activity

Don't corrupt the FILE buffer when printing to a non-writable stream

Browse Source 
init_buffer decremented the write pointer even when putc_unlocked failed,
turning a null pointer into (char*)-1 that print then wrote through, e.g.
when printing to a stream opened for reading. Report an error instead.
This commit is contained in:
Victor Zverovich 2026-11-08 08:04:42 -08:00
parent e3d10c994d
commit aa99376370
2 changed files with 32 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
include/fmt/format-inl.h
View File

@ -1521,11 +1521,14 @@ template <typename F> class glibc_file : public file_base<F> {
return (this->file_->_flags & unbuffered) == 0;
}
void init_buffer() {
if (this->file_->_IO_write_ptr < this->file_->_IO_write_end) return;
// Returns false if the buffer cannot be initialized, e.g. because the file
// is not open for writing.
auto init_buffer() -> bool {
if (this->file_->_IO_write_ptr < this->file_->_IO_write_end) return true;
// Force buffer initialization by placing and removing a char in a buffer.
putc_unlocked(0, this->file_);
if (putc_unlocked(0, this->file_) == EOF) return false;
--this->file_->_IO_write_ptr;
return true;
}
// Returns the file's read buffer.
@ -1570,12 +1573,13 @@ template <typename F> class apple_file : public file_base<F> {
return (this->file_->_flags & unbuffered) == 0;
}
void init_buffer() {
if (this->file_->_p) return;
auto init_buffer() -> bool {
if (this->file_->_p) return true;
// Force buffer initialization by placing and removing a char in a buffer.
putc_unlocked(0, this->file_);
if (putc_unlocked(0, this->file_) == EOF) return false;
--this->file_->_p;
++this->file_->_w;
return true;
}
auto get_read_buffer() const -> span<const char> {
@ -1612,7 +1616,7 @@ template <typename F> class fallback_file : public file_base<F> {
auto is_buffered() const -> bool { return false; }
auto needs_flush() const -> bool { return false; }
void init_buffer() {}
auto init_buffer() -> bool { return true; }
auto get_read_buffer() const -> span<const char> {
return {&next_, has_next_ ? 1u : 0u};
@ -1665,6 +1669,14 @@ class file_print_buffer<F, enable_if_t<has_flockfile<F>::value>>
private:
file_ref file_;
void unlock() {
F* f = file_; // Make funlockfile depend on the template parameter F.
#ifdef __SANITIZE_THREAD__
__tsan_release(f);
#endif
funlockfile(f); // for the system API detection to work.
}
static void grow(buffer<char>& base, size_t) {
auto& self = static_cast<file_print_buffer&>(base);
self.file_.advance_write_buffer(self.size());
@ -1681,18 +1693,18 @@ class file_print_buffer<F, enable_if_t<has_flockfile<F>::value>>
#ifdef __SANITIZE_THREAD__
__tsan_acquire(f);
#endif
file_.init_buffer();
if (!file_.init_buffer()) {
int error_code = errno;
unlock();
FMT_THROW(system_error(error_code, FMT_STRING("cannot write to file")));
}
auto buf = file_.get_write_buffer();
set(buf.data, buf.size);
}
~file_print_buffer() {
file_.advance_write_buffer(size());
bool flush = file_.needs_flush();
F* f = file_; // Make funlockfile depend on the template parameter F.
#ifdef __SANITIZE_THREAD__
__tsan_release(f);
#endif
funlockfile(f); // for the system API detection to work.
unlock();
if (flush) fflush(file_);
}
};

7
test/format-test.cc
View File

@ -2875,6 +2875,13 @@ TEST(format_test, print_to_broken_pipe) {
}
std::signal(SIGPIPE, old_handler);
}
TEST(format_test, print_to_read_only_file) {
auto pipe = fmt::pipe();
auto read_end = pipe.read_end.fdopen("r");
EXPECT_THROW(fmt::print(read_end.get(), "{}", std::string(100, 'x')),
std::system_error);
}
#endif // FMT_USE_FCNTL
// Only defined after the test case.