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QProcess/Unix: move strerror() up from child to parent

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In theory, there's nothing wrong with having it in the child process. In
practice, we've found that strerror/malloc can hang: if an application-
wide lock was held by another thread before fork(), the child process
could wait forever for an unlocking that will not happen (no threads
running). See https://sourceware.org/bugzilla/show_bug.cgi?id=19431

As an added bonus, we now use qt_error_string(), which may produce
slightly different text from strerror.

[ChangeLog][QtCore][QProcess] Added a workaround for a rare race-
condition bug in some C libraries that caused the child process started
by QProcess to hang after trying to launch a non-existent executable or
change to a non-existent directory.

Task-number: QTBUG-61634
Change-Id: I1eba2b016de74620bfc8fffd14cbce4b9f9af69b
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
This commit is contained in:
Thiago Macieira 2017-06-26 16:02:05 -07:00
parent 5d31b52a12
commit ffe8884ac3
1 changed files with 19 additions and 27 deletions
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46
src/corelib/io/qprocess_unix.cpp
View File

@ -146,10 +146,6 @@ QProcessEnvironment QProcessEnvironment::systemEnvironment()
#if QT_CONFIG(process)
// POSIX requires PIPE_BUF to be 512 or larger
// so we will use 512
static const int errorBufferMax = 512;
namespace {
struct QProcessPoller
{
@ -548,11 +544,18 @@ void QProcessPrivate::startProcess()
}
}
struct ChildError
{
int code;
char function[8];
};
void QProcessPrivate::execChild(const char *workingDir, char **path, char **argv, char **envp)
{
::signal(SIGPIPE, SIG_DFL); // reset the signal that we ignored
Q_Q(QProcess);
ChildError error = { 0, {} }; // force zeroing of function[8]
// copy the stdin socket if asked to (without closing on exec)
if (inputChannelMode != QProcess::ForwardedInputChannel)
@ -575,9 +578,9 @@ void QProcessPrivate::execChild(const char *workingDir, char **path, char **argv
qt_safe_close(childStartedPipe[0]);
// enter the working directory
const char *callthatfailed = "chdir: ";
if (workingDir && QT_CHDIR(workingDir) == -1) {
// failed, stop the process
strcpy(error.function, "chdir");
goto report_errno;
}
@ -587,7 +590,7 @@ void QProcessPrivate::execChild(const char *workingDir, char **path, char **argv
// execute the process
if (!envp) {
qt_safe_execvp(argv[0], argv);
callthatfailed = "execvp: ";
strcpy(error.function, "execvp");
} else {
if (path) {
char **arg = path;
@ -605,33 +608,22 @@ void QProcessPrivate::execChild(const char *workingDir, char **path, char **argv
#endif
qt_safe_execve(argv[0], argv, envp);
}
callthatfailed = "execve: ";
strcpy(error.function, "execve");
}
// notify failure
// we're running in the child process, so we don't need to be thread-safe;
// we can use strerror
// don't use strerror or any other routines that may allocate memory, since
// some buggy libc versions can deadlock on locked mutexes.
report_errno:
const char *msg = strerror(errno);
#if defined (QPROCESS_DEBUG)
fprintf(stderr, "QProcessPrivate::execChild() failed (%s), notifying parent process\n", msg);
#endif
qt_safe_write(childStartedPipe[1], callthatfailed, strlen(callthatfailed));
qt_safe_write(childStartedPipe[1], msg, strlen(msg));
qt_safe_close(childStartedPipe[1]);
error.code = errno;
qt_safe_write(childStartedPipe[1], &error, sizeof(error));
childStartedPipe[1] = -1;
}
bool QProcessPrivate::processStarted(QString *errorMessage)
{
char buf[errorBufferMax];
int i = 0;
int ret;
do {
ret = qt_safe_read(childStartedPipe[0], buf + i, sizeof buf - i);
if (ret > 0)
i += ret;
} while (ret > 0 && i < int(sizeof buf));
ChildError buf;
int ret = qt_safe_read(childStartedPipe[0], &buf, sizeof(buf));
if (startupSocketNotifier) {
startupSocketNotifier->setEnabled(false);
@ -646,10 +638,10 @@ bool QProcessPrivate::processStarted(QString *errorMessage)
#endif
// did we read an error message?
if ((i > 0) && errorMessage)
*errorMessage = QString::fromLocal8Bit(buf, i);
if (ret > 0 && errorMessage)
*errorMessage = QLatin1String(buf.function) + QLatin1String(": ") + qt_error_string(buf.code);
return i <= 0;
return ret <= 0;
}
qint64 QProcessPrivate::bytesAvailableInChannel(const Channel *channel) const