run-command: prepare command before forking

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>

diff --git a/run-command.c b/run-command.c
index 574b81d3e82bbe6de31b141c3951ab408daad5e6..d8d1437954259babb39d0df6322e0f59e77239aa 100644 (file)
--- a/run-command.c
+++ b/run-command.c
@@ -220,18 +220,6 @@ static const char **prepare_shell_cmd(struct argv_array *out, const char **argv)
        return out->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;
 
 #ifndef GIT_WINDOWS_NATIVE
 static int child_notifier = -1;
 


@@ -244,6 +232,21 @@ static void notify_parent(void)
         */
        xwrite(child_notifier, "", 1);
 }
         */
        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)
 #endif
 
 static inline void set_cloexec(int fd)


@@ -372,9 +375,13 @@ int start_command(struct child_process *cmd)
 #ifndef GIT_WINDOWS_NATIVE
 {
        int notify_pipe[2];
 #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;
 
        if (pipe(notify_pipe))
                notify_pipe[0] = notify_pipe[1] = -1;
 

+       prepare_cmd(&argv, cmd);
+

        cmd->pid = fork();
        failed_errno = errno;
        if (!cmd->pid) {
        cmd->pid = fork();
        failed_errno = errno;
        if (!cmd->pid) {


@@ -437,12 +444,9 @@ int start_command(struct child_process *cmd)
                                        unsetenv(*cmd->env);
                        }
                }
                                        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],
                if (errno == ENOENT) {
                        if (!cmd->silent_exec_failure)
                                error("cannot run %s: %s", cmd->argv[0],


@@ -458,7 +462,7 @@ int start_command(struct child_process *cmd)
                mark_child_for_cleanup(cmd->pid, cmd);
 
        /*
                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,
         * 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 @@ int start_command(struct child_process *cmd)
        close(notify_pipe[1]);
        if (read(notify_pipe[0], &notify_pipe[1], 1) == 1) {
                /*
        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);
                 * failed. Errors have been reported to our stderr.
                 */
                wait_or_whine(cmd->pid, cmd->argv[0], 0);


@@ -475,6 +479,8 @@ int start_command(struct child_process *cmd)
                cmd->pid = -1;
        }
        close(notify_pipe[0]);
                cmd->pid = -1;
        }
        close(notify_pipe[0]);

+
+       argv_array_clear(&argv);

 }
 #else
 {
 }
 #else
 {