pipecmd: don't close stderr/stdout/stdin in parent when &pipecmd_preserve

This was reported and fixed by @m-schmoock for stderr, but I decided to
rework to make it clearer and cover the other cases:

	https://github.com/ElementsProject/lightning/pull/2321/commits/67dad01549f876e5e620eeffe2f1e78c35bd0f03Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

ccan/pipecmd/pipecmd.c

@@ -47,68 +47,76 @@ pid_t pipecmdarr(int *fd_tochild, int *fd_fromchild, int *fd_errfromchild,
 		 char *const *arr)
 {
 	int tochild[2], fromchild[2], errfromchild[2], execfail[2];
+	/* fds for parent to close */
+	int par_close[4], num_par_close = 0;
+	/* fds for child to close */
+	int child_close[4], num_child_close = 0;
 	pid_t childpid;
 	int err;
 
 	if (fd_tochild) {
 		if (fd_tochild == &pipecmd_preserve) {
 			tochild[0] = STDIN_FILENO;
-			fd_tochild = NULL;
-		} else if (pipe(tochild) != 0)
+		} else if (pipe(tochild) == 0) {
+			par_close[num_par_close++] = tochild[0];
+			child_close[num_child_close++] = tochild[1];
+		} else
 			goto fail;
 	} else {
 		tochild[0] = open("/dev/null", O_RDONLY);
 		if (tochild[0] < 0)
 			goto fail;
+		par_close[num_par_close++] = tochild[0];
 	}
 	if (fd_fromchild) {
 		if (fd_fromchild == &pipecmd_preserve) {
 			fromchild[1] = STDOUT_FILENO;
-			fd_fromchild = NULL;
-		} else if (pipe(fromchild) != 0)
-			goto close_tochild_fail;
+		} else if (pipe(fromchild) == 0) {
+			par_close[num_par_close++] = fromchild[1];
+			child_close[num_child_close++] = fromchild[0];
+		} else
+			goto fail;
 	} else {
 		fromchild[1] = open("/dev/null", O_WRONLY);
 		if (fromchild[1] < 0)
-			goto close_tochild_fail;
+			goto fail;
+		par_close[num_par_close++] = fromchild[1];
 	}
 	if (fd_errfromchild) {
 		if (fd_errfromchild == &pipecmd_preserve) {
 			errfromchild[1] = STDERR_FILENO;
-			fd_errfromchild = NULL;
 		} else if (fd_errfromchild == fd_fromchild) {
 			errfromchild[0] = fromchild[0];
 			errfromchild[1] = fromchild[1];
-		} else {
-			if (pipe(errfromchild) != 0)
-				goto close_fromchild_fail;
-		}
+		} else if (pipe(errfromchild) == 0) {
+			par_close[num_par_close++] = errfromchild[1];
+			child_close[num_child_close++] = errfromchild[0];
+		} else
+			goto fail;
 	} else {
 		errfromchild[1] = open("/dev/null", O_WRONLY);
 		if (errfromchild[1] < 0)
-			goto close_fromchild_fail;
+			goto fail;
+		par_close[num_par_close++] = errfromchild[1];
 	}
 
 	if (pipe(execfail) != 0)
-		goto close_errfromchild_fail;
+		goto fail;
+
+	par_close[num_par_close++] = execfail[1];
+	child_close[num_child_close++] = execfail[0];
 
 	if (fcntl(execfail[1], F_SETFD, fcntl(execfail[1], F_GETFD)
 		  | FD_CLOEXEC) < 0)
-		goto close_execfail_fail;
+		goto fail;
 
 	childpid = fork();
 	if (childpid < 0)
-		goto close_execfail_fail;
+		goto fail;
 
 	if (childpid == 0) {
-		if (fd_tochild)
-			close(tochild[1]);
-		if (fd_fromchild)
-			close(fromchild[0]);
-		if (fd_errfromchild && fd_errfromchild != fd_fromchild)
-			close(errfromchild[0]);
-
-		close(execfail[0]);
+		for (int i = 0; i < num_child_close; i++)
+			close(child_close[i]);
 
 		// Child runs command.
 		if (tochild[0] != STDIN_FILENO) {
@@ -140,10 +148,9 @@ pid_t pipecmdarr(int *fd_tochild, int *fd_fromchild, int *fd_errfromchild,
 		exit(127);
 	}
 
-	close(tochild[0]);
-	close(fromchild[1]);
-	close(errfromchild[1]);
-	close(execfail[1]);
+	for (int i = 0; i < num_par_close; i++)
+		close(par_close[i]);
+
 	/* Child will close this without writing on successful exec. */
 	if (read(execfail[0], &err, sizeof(err)) == sizeof(err)) {
 		close(execfail[0]);
@@ -152,30 +159,17 @@ pid_t pipecmdarr(int *fd_tochild, int *fd_fromchild, int *fd_errfromchild,
 		return -1;
 	}
 	close(execfail[0]);
-	if (fd_tochild)
+	if (fd_tochild && fd_tochild != &pipecmd_preserve)
 		*fd_tochild = tochild[1];
-	if (fd_fromchild)
+	if (fd_fromchild && fd_fromchild != &pipecmd_preserve)
 		*fd_fromchild = fromchild[0];
-	if (fd_errfromchild)
+	if (fd_errfromchild && fd_errfromchild != &pipecmd_preserve)
 		*fd_errfromchild = errfromchild[0];
 	return childpid;
 
-close_execfail_fail:
-	close_noerr(execfail[0]);
-	close_noerr(execfail[1]);
-close_errfromchild_fail:
-	if (fd_errfromchild)
-		close_noerr(errfromchild[0]);
-	close_noerr(errfromchild[1]);
-close_fromchild_fail:
-	if (fd_fromchild)
-		close_noerr(fromchild[0]);
-	close_noerr(fromchild[1]);
-close_tochild_fail:
-	close_noerr(tochild[0]);
-	if (fd_tochild)
-		close_noerr(tochild[1]);
 fail:
+	for (int i = 0; i < num_par_close; i++)
+		close_noerr(par_close[i]);
 	return -1;
 }