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run-command: prepare command before forking

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According to [1] we need to only call async-signal-safe operations between fork
and exec.  Using malloc to build the argv array isn't async-signal-safe.

In order to avoid allocation between 'fork()' and 'exec()' prepare the
argv array used in the exec call prior to forking the process.

[1] http://pubs.opengroup.org/onlinepubs/009695399/functions/fork.html

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Brandon Williams 2017-04-19 16:13:19 -07:00 committed by Junio C Hamano
parent c2d3119d7b
commit 3967e25be1
1 changed files with 26 additions and 20 deletions
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46
run-command.c
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@ -220,18 +220,6 @@ static const char **prepare_shell_cmd(struct argv_array *out, const char **argv)
return out->argv;
}
#ifndef GIT_WINDOWS_NATIVE
static int execv_shell_cmd(const char **argv)
{
struct argv_array nargv = ARGV_ARRAY_INIT;
prepare_shell_cmd(&nargv, argv);
trace_argv_printf(nargv.argv, "trace: exec:");
sane_execvp(nargv.argv[0], (char **)nargv.argv);
argv_array_clear(&nargv);
return -1;
}
#endif
#ifndef GIT_WINDOWS_NATIVE
static int child_notifier = -1;
@ -244,6 +232,21 @@ static void notify_parent(void)
*/
xwrite(child_notifier, "", 1);
}
static void prepare_cmd(struct argv_array *out, const struct child_process *cmd)
{
if (!cmd->argv[0])
die("BUG: command is empty");
if (cmd->git_cmd) {
argv_array_push(out, "git");
argv_array_pushv(out, cmd->argv);
} else if (cmd->use_shell) {
prepare_shell_cmd(out, cmd->argv);
} else {
argv_array_pushv(out, cmd->argv);
}
}
#endif
static inline void set_cloexec(int fd)
@ -372,9 +375,13 @@ fail_pipe:
#ifndef GIT_WINDOWS_NATIVE
{
int notify_pipe[2];
struct argv_array argv = ARGV_ARRAY_INIT;
if (pipe(notify_pipe))
notify_pipe[0] = notify_pipe[1] = -1;
prepare_cmd(&argv, cmd);
cmd->pid = fork();
failed_errno = errno;
if (!cmd->pid) {
@ -437,12 +444,9 @@ fail_pipe:
unsetenv(*cmd->env);
}
}
if (cmd->git_cmd)
execv_git_cmd(cmd->argv);
else if (cmd->use_shell)
execv_shell_cmd(cmd->argv);
else
sane_execvp(cmd->argv[0], (char *const*) cmd->argv);
sane_execvp(argv.argv[0], (char *const *) argv.argv);
if (errno == ENOENT) {
if (!cmd->silent_exec_failure)
error("cannot run %s: %s", cmd->argv[0],
@ -458,7 +462,7 @@ fail_pipe:
mark_child_for_cleanup(cmd->pid, cmd);
/*
* Wait for child's execvp. If the execvp succeeds (or if fork()
* 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.
* Note that use of this infrastructure is completely advisory,
@ -467,7 +471,7 @@ fail_pipe:
close(notify_pipe[1]);
if (read(notify_pipe[0], &notify_pipe[1], 1) == 1) {
/*
* At this point we know that fork() succeeded, but execvp()
* 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);
@ -475,6 +479,8 @@ fail_pipe:
cmd->pid = -1;
}
close(notify_pipe[0]);
argv_array_clear(&argv);
}
#else
{