[PATCH v6 06/11] run-command: prepare child environment before forking

[Brandon Williams <bmwill@google.com>]

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

Switch to using 'execve()' so that the construct child environment can
used in the exec'd process.

Signed-off-by: Brandon Williams <bmwill@google.com>
---
 run-command.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 56 insertions(+), 10 deletions(-)

diff --git a/run-command.c b/run-command.c
index 1c7a3b611..15e2e74a7 100644
--- a/run-command.c
+++ b/run-command.c
@@ -267,6 +267,55 @@ static void prepare_cmd(struct argv_array *out, const struct child_process *cmd)
 		}
 	}
 }
+
+static char **prep_childenv(const char *const *deltaenv)
+{
+	extern char **environ;
+	char **childenv;
+	struct string_list env = STRING_LIST_INIT_DUP;
+	struct strbuf key = STRBUF_INIT;
+	const char *const *p;
+	int i;
+
+	/* Construct a sorted string list consisting of the current environ */
+	for (p = (const char *const *) environ; p && *p; p++) {
+		const char *equals = strchr(*p, '=');
+
+		if (equals) {
+			strbuf_reset(&key);
+			strbuf_add(&key, *p, equals - *p);
+			string_list_append(&env, key.buf)->util = (void *) *p;
+		} else {
+			string_list_append(&env, *p)->util = (void *) *p;
+		}
+	}
+	string_list_sort(&env);
+
+	/* Merge in 'deltaenv' with the current environ */
+	for (p = deltaenv; p && *p; p++) {
+		const char *equals = strchr(*p, '=');
+
+		if (equals) {
+			/* ('key=value'), insert or replace entry */
+			strbuf_reset(&key);
+			strbuf_add(&key, *p, equals - *p);
+			string_list_insert(&env, key.buf)->util = (void *) *p;
+		} else {
+			/* otherwise ('key') remove existing entry */
+			string_list_remove(&env, *p, 0);
+		}
+	}
+
+	/* Create an array of 'char *' to be used as the childenv */
+	childenv = xmalloc((env.nr + 1) * sizeof(char *));
+	for (i = 0; i < env.nr; i++)
+		childenv[i] = env.items[i].util;
+	childenv[env.nr] = NULL;
+
+	string_list_clear(&env, 0);
+	strbuf_release(&key);
+	return childenv;
+}
 #endif
 
 static inline void set_cloexec(int fd)
@@ -395,12 +444,14 @@ int start_command(struct child_process *cmd)
 #ifndef GIT_WINDOWS_NATIVE
 {
 	int notify_pipe[2];
+	char **childenv;
 	struct argv_array argv = ARGV_ARRAY_INIT;
 
 	if (pipe(notify_pipe))
 		notify_pipe[0] = notify_pipe[1] = -1;
 
 	prepare_cmd(&argv, cmd);
+	childenv = prep_childenv(cmd->env);
 
 	cmd->pid = fork();
 	failed_errno = errno;
@@ -456,14 +507,6 @@ 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);
-			}
-		}
 
 		/*
 		 * Attempt to exec using the command and arguments starting at
@@ -471,9 +514,11 @@ int start_command(struct child_process *cmd)
 		 * be used in the event exec failed with ENOEXEC at which point
 		 * we will try to interpret the command using 'sh'.
 		 */
-		execv(argv.argv[1], (char *const *) argv.argv + 1);
+		execve(argv.argv[1], (char *const *) argv.argv + 1,
+		       (char *const *) childenv);
 		if (errno == ENOEXEC)
-			execv(argv.argv[0], (char *const *) argv.argv);
+			execve(argv.argv[0], (char *const *) argv.argv,
+			       (char *const *) childenv);
 
 		if (errno == ENOENT) {
 			if (!cmd->silent_exec_failure)
@@ -509,6 +554,7 @@ int start_command(struct child_process *cmd)
 	close(notify_pipe[0]);
 
 	argv_array_clear(&argv);
+	free(childenv);
 }
 #else
 {
-- 
2.12.2.816.g2cccc81164-goog