[PATCH 4/5] run-command: prepare child environment before forking

[Brandon Williams]

In order to avoid allocation between 'fork()' and 'exec()' prepare the
environment to be used in the child process prior to forking.

Signed-off-by: Brandon Williams <bmw...@google.com>
---
 run-command.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 75 insertions(+), 9 deletions(-)

diff --git a/run-command.c b/run-command.c
index 029d41463..84c63b209 100644
--- a/run-command.c
+++ b/run-command.c
@@ -291,6 +291,75 @@ static int wait_or_whine(pid_t pid, const char *argv0, int 
in_signal)
        return code;
 }
 
+static int env_isequal(const char *e1, const char *e2)
+{
+       for (;;) {
+               char c1 = *e1++;
+               char c2 = *e2++;
+               c1 = (c1 == '=') ? '\0' : tolower(c1);
+               c2 = (c2 == '=') ? '\0' : tolower(c2);
+
+               if (c1 != c2)
+                       return 0;
+               if (c1 == '\0')
+                       return 1;
+       }
+}
+
+static int searchenv(char **env, const char *name)
+{
+       int pos = 0;
+
+       for (; env[pos]; pos++)
+               if (env_isequal(env[pos], name))
+                       break;
+
+       return pos;
+}
+
+static int do_putenv(char **env, int env_nr, const char *name)
+{
+       int pos = searchenv(env, name);
+
+       if (strchr(name, '=')) {
+               /* ('key=value'), insert of replace entry */
+               if (pos >= env_nr)
+                       env_nr++;
+               env[pos] = (char *) name;
+       } else if (pos < env_nr) {
+               /* otherwise ('key') remove existing entry */
+               env_nr--;
+               memmove(&env[pos], &env[pos + 1],
+                       (env_nr - pos) * sizeof(char *));
+               env[env_nr] = NULL;
+       }
+
+       return env_nr;
+}
+
+static char **prep_childenv(const char *const *deltaenv)
+{
+       char **childenv;
+       int childenv_nr = 0, childenv_alloc = 0;
+       int i;
+
+       for (i = 0; environ[i]; i++)
+               childenv_nr++;
+       for (i = 0; deltaenv && deltaenv[i]; i++)
+               childenv_alloc++;
+       /* Add one for the NULL termination */
+       childenv_alloc += childenv_nr + 1;
+
+       childenv = xcalloc(childenv_alloc, sizeof(char *));
+       memcpy(childenv, environ, childenv_nr * sizeof(char *));
+
+       /* merge in deltaenv */
+       for (i = 0; deltaenv && deltaenv[i]; i++)
+               childenv_nr = do_putenv(childenv, childenv_nr, deltaenv[i]);
+
+       return childenv;
+}
+
 int start_command(struct child_process *cmd)
 {
        int need_in, need_out, need_err;
@@ -365,12 +434,15 @@ int start_command(struct child_process *cmd)
 #ifndef GIT_WINDOWS_NATIVE
 {
        int notify_pipe[2];
+       char **childenv;
        FILE *child_err = NULL;
        struct argv_array argv = ARGV_ARRAY_INIT;
 
        if (pipe(notify_pipe))
                notify_pipe[0] = notify_pipe[1] = -1;
 
+       childenv = prep_childenv(cmd->env);
+
        if (cmd->no_stderr || need_err) {
                int child_err_fd = dup(2);
                set_cloexec(child_err_fd);
@@ -437,16 +509,9 @@ 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);
-               if (cmd->env) {
-                       for (; *cmd->env; cmd->env++) {
-                               if (strchr(*cmd->env, '='))
-                                       putenv((char *)*cmd->env);
-                               else
-                                       unsetenv(*cmd->env);
-                       }
-               }
 
-               sane_execvpe(argv.argv[0], (char *const*) argv.argv, NULL);
+               sane_execvpe(argv.argv[0], (char *const*) argv.argv,
+                            (char *const*) childenv);
 
                if (errno == ENOENT) {
                        if (!cmd->silent_exec_failure)
@@ -483,6 +548,7 @@ int start_command(struct child_process *cmd)
 
        if (child_err)
                fclose(child_err);
+       free(childenv);
        argv_array_clear(&argv);
 }
 #else
-- 
2.12.2.715.g7642488e1d-goog