All of our standard error handling paths have the potential to
call malloc or take stdio locks; so we must avoid them inside
the forked child.
Instead, the child only writes an 8 byte struct atomically to
the parent through the notification pipe to propagate an error.
All user-visible error reporting happens from the parent;
even avoiding functions like atexit(3) and exit(3).
Helped-by: Eric Wong <e@xxxxxxxxx>
Signed-off-by: Brandon Williams <bmwill@xxxxxxxxxx>
---
run-command.c | 121 ++++++++++++++++++++++++++++++++++++++++++----------------
1 file changed, 89 insertions(+), 32 deletions(-)
diff --git a/run-command.c b/run-command.c
index ee2c680ab..25b487c35 100644
--- a/run-command.c
+++ b/run-command.c
@@ -211,14 +211,82 @@ static const char **prepare_shell_cmd(struct argv_array *out, const char **argv)
#ifndef GIT_WINDOWS_NATIVE
static int child_notifier = -1;
-static void notify_parent(void)
+enum child_errcode {
+ CHILD_ERR_CHDIR,
+ CHILD_ERR_ENOENT,
+ CHILD_ERR_SILENT,
+ CHILD_ERR_ERRNO,
+};
+
+struct child_err {
+ enum child_errcode err;
+ int syserr; /* errno */
+};
+
+static void child_die(enum child_errcode err)
{
- /*
- * execvp failed. If possible, we'd like to let start_command
- * know, so failures like ENOENT can be handled right away; but
- * otherwise, finish_command will still report the error.
- */
- xwrite(child_notifier, "", 1);
+ struct child_err buf;
+
+ buf.err = err;
+ buf.syserr = errno;
+
+ /* write(2) on buf smaller than PIPE_BUF (min 512) is atomic: */
+ xwrite(child_notifier, &buf, sizeof(buf));
+ _exit(1);
+}
+
+/*
+ * parent will make it look like the child spewed a fatal error and died
+ * this is needed to prevent changes to t0061.
+ */
+static void fake_fatal(const char *err, va_list params)
+{
+ vreportf("fatal: ", err, params);
+}
+
+static void child_error_fn(const char *err, va_list params)
+{
+ const char msg[] = "error() should not be called in child\n";
+ xwrite(2, msg, sizeof(msg) - 1);
+}
+
+static void child_warn_fn(const char *err, va_list params)
+{
+ const char msg[] = "warn() should not be called in child\n";
+ xwrite(2, msg, sizeof(msg) - 1);
+}
+
+static void NORETURN child_die_fn(const char *err, va_list params)
+{
+ const char msg[] = "die() should not be called in child\n";
+ xwrite(2, msg, sizeof(msg) - 1);
+ _exit(2);
+}
+
+/* this runs in the parent process */
+static void child_err_spew(struct child_process *cmd, struct child_err *cerr)
+{
+ static void (*old_errfn)(const char *err, va_list params);
+
+ old_errfn = get_error_routine();
+ set_error_routine(fake_fatal);
+ errno = cerr->syserr;
+
+ switch (cerr->err) {
+ case CHILD_ERR_CHDIR:
+ error_errno("exec '%s': cd to '%s' failed",
+ cmd->argv[0], cmd->dir);
+ break;
+ case CHILD_ERR_ENOENT:
+ error_errno("cannot run %s", cmd->argv[0]);
+ break;
+ case CHILD_ERR_SILENT:
+ break;
+ case CHILD_ERR_ERRNO:
+ error_errno("cannot exec '%s'", cmd->argv[0]);
+ break;
+ }
+ set_error_routine(old_errfn);
}
static void prepare_cmd(struct argv_array *out, const struct child_process *cmd)
@@ -361,13 +429,6 @@ static int wait_or_whine(pid_t pid, const char *argv0, int in_signal)
code += 128;
} else if (WIFEXITED(status)) {
code = WEXITSTATUS(status);
- /*
- * Convert special exit code when execvp failed.
- */
- if (code == 127) {
- code = -1;
- failed_errno = ENOENT;
- }
} else {
error("waitpid is confused (%s)", argv0);
}
@@ -455,6 +516,7 @@ int start_command(struct child_process *cmd)
int null_fd = -1;
char **childenv;
struct argv_array argv = ARGV_ARRAY_INIT;
+ struct child_err cerr;
if (pipe(notify_pipe))
notify_pipe[0] = notify_pipe[1] = -1;
@@ -473,20 +535,16 @@ int start_command(struct child_process *cmd)
failed_errno = errno;
if (!cmd->pid) {
/*
- * Redirect the channel to write syscall error messages to
- * before redirecting the process's stderr so that all die()
- * in subsequent call paths use the parent's stderr.
+ * Ensure the default die/error/warn routines do not get
+ * called, they can take stdio locks and malloc.
*/
- if (cmd->no_stderr || need_err) {
- int child_err = dup(2);
- set_cloexec(child_err);
- set_error_handle(fdopen(child_err, "w"));
- }
+ set_die_routine(child_die_fn);
+ set_error_routine(child_error_fn);
+ set_warn_routine(child_warn_fn);
close(notify_pipe[0]);
set_cloexec(notify_pipe[1]);
child_notifier = notify_pipe[1];
- atexit(notify_parent);
if (cmd->no_stdin)
dup2(null_fd, 0);
@@ -521,8 +579,7 @@ int start_command(struct child_process *cmd)
}
if (cmd->dir && chdir(cmd->dir))
- die_errno("exec '%s': cd to '%s' failed", cmd->argv[0],
- cmd->dir);
+ child_die(CHILD_ERR_CHDIR);
/*
* Attempt to exec using the command and arguments starting at
@@ -537,12 +594,11 @@ int start_command(struct child_process *cmd)
(char *const *) childenv);
if (errno == ENOENT) {
- if (!cmd->silent_exec_failure)
- error("cannot run %s: %s", cmd->argv[0],
- strerror(ENOENT));
- exit(127);
+ if (cmd->silent_exec_failure)
+ child_die(CHILD_ERR_SILENT);
+ child_die(CHILD_ERR_ENOENT);
} else {
- die_errno("cannot exec '%s'", cmd->argv[0]);
+ child_die(CHILD_ERR_ERRNO);
}
}
if (cmd->pid < 0)
@@ -553,17 +609,18 @@ int start_command(struct child_process *cmd)
/*
* Wait for child's exec. If the exec succeeds (or if fork()
* failed), EOF is seen immediately by the parent. Otherwise, the
- * child process sends a single byte.
+ * child process sends a child_err struct.
* Note that use of this infrastructure is completely advisory,
* therefore, we keep error checks minimal.
*/
close(notify_pipe[1]);
- if (read(notify_pipe[0], ¬ify_pipe[1], 1) == 1) {
+ if (xread(notify_pipe[0], &cerr, sizeof(cerr)) == sizeof(cerr)) {
/*
* At this point we know that fork() succeeded, but exec()
* failed. Errors have been reported to our stderr.
*/
wait_or_whine(cmd->pid, cmd->argv[0], 0);
+ child_err_spew(cmd, &cerr);
failed_errno = errno;
cmd->pid = -1;
}
--
2.12.2.762.g0e3151a226-goog