Use /dev/null for update hook stdin.

Currently the update hook invoked by receive-pack has its stdin
connected to the pushing client.  The hook shouldn't attempt to
read from this stream, and doing so may consume data that was
meant for receive-pack.  Instead we should give the update hook
/dev/null as its stdin, ensuring that it always receives EOF and
doesn't disrupt the protocol if it attempts to read any data.

The post-update hook is similar, as it gets invoked with /dev/null
on stdin to prevent the hook from reading data from the client.
Previously we had invoked it with stdout also connected to /dev/null,
throwing away anything on stdout, to prevent client protocol errors.
Instead we should redirect stdout to stderr, like we do with the
update hook.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

receive-pack.c

@@ -73,7 +73,8 @@ static int run_update_hook(const char *refname,
 
 	if (access(update_hook, X_OK) < 0)
 		return 0;
-	code = run_command_opt(RUN_COMMAND_STDOUT_TO_STDERR,
+	code = run_command_opt(RUN_COMMAND_NO_STDIN
+		| RUN_COMMAND_STDOUT_TO_STDERR,
 		update_hook, refname, old_hex, new_hex, NULL);
 	switch (code) {
 	case 0:
@@ -188,7 +189,8 @@ static void run_update_post_hook(struct command *cmd)
 		argc++;
 	}
 	argv[argc] = NULL;
-	run_command_v_opt(argv, RUN_COMMAND_NO_STDIO);
+	run_command_v_opt(argv, RUN_COMMAND_NO_STDIN
+		| RUN_COMMAND_STDOUT_TO_STDERR);
 }
 
 /*

run-command.c

@@ -9,12 +9,12 @@ int run_command_v_opt(const char **argv, int flags)
 	if (pid < 0)
 		return -ERR_RUN_COMMAND_FORK;
 	if (!pid) {
-		if (flags & RUN_COMMAND_NO_STDIO) {
+		if (flags & RUN_COMMAND_NO_STDIN) {
 			int fd = open("/dev/null", O_RDWR);
 			dup2(fd, 0);
-			dup2(fd, 1);
 			close(fd);
-		} else if (flags & RUN_COMMAND_STDOUT_TO_STDERR)
+		}
+		if (flags & RUN_COMMAND_STDOUT_TO_STDERR)
 			dup2(2, 1);
 		if (flags & RUN_GIT_CMD) {
 			execv_git_cmd(argv);

run-command.h

@@ -11,7 +11,7 @@ enum {
 	ERR_RUN_COMMAND_WAITPID_NOEXIT,
 };
 
-#define RUN_COMMAND_NO_STDIO 1
+#define RUN_COMMAND_NO_STDIN 1
 #define RUN_GIT_CMD	     2	/*If this is to be git sub-command */
 #define RUN_COMMAND_STDOUT_TO_STDERR 4
 int run_command_v_opt(const char **argv, int opt);