lightningd/jsonrpc.c: Set JSON-RPC socket permissions by command line.

Changelog-Added: Can now set the permissions on the JSON-RPC socket by `--rpc-file-mode`.

doc/lightningd-config.5

@@ -188,6 +188,14 @@ cause it to reopen this file (useful for log rotation)\.
 Set JSON-RPC socket (or /dev/tty), such as for \fBlightning-cli\fR(1)\.
 
 
+ \fBrpc-file-mode\fR=\fIMODE\fR
+Set JSON-RPC socket file mode, as a 4-digit octal number\.
+Default is 0600, meaning only the user that launched lightningd
+can command it\.
+Set to 0660 to allow users with the same group to access the RPC
+as well\.
+
+
  \fBdaemon\fR
 Run in the background, suppress stdout and stderr\.
 

doc/lightningd-config.5.md

@@ -149,6 +149,13 @@ cause it to reopen this file (useful for log rotation).
  **rpc-file**=*PATH*
 Set JSON-RPC socket (or /dev/tty), such as for lightning-cli(1).
 
+ **rpc-file-mode**=*MODE*
+Set JSON-RPC socket file mode, as a 4-digit octal number.
+Default is 0600, meaning only the user that launched lightningd
+can command it.
+Set to 0660 to allow users with the same group to access the RPC
+as well.
+
  **daemon**
 Run in the background, suppress stdout and stderr.
 

lightningd/jsonrpc.c

@@ -1074,7 +1074,7 @@ bool command_check_only(const struct command *cmd)
 void jsonrpc_listen(struct jsonrpc *jsonrpc, struct lightningd *ld)
 {
 	struct sockaddr_un addr;
-	int fd, old_umask;
+	int fd, old_umask, new_umask;
 	const char *rpc_filename = ld->rpc_filename;
 
 	/* Should not initialize it twice. */
@@ -1103,8 +1103,9 @@ void jsonrpc_listen(struct jsonrpc *jsonrpc, struct lightningd *ld)
 		errx(1, "rpc filename '%s' in use", rpc_filename);
 	unlink(rpc_filename);
 
-	/* This file is only rw by us! */
-	old_umask = umask(0177);
+	/* Set the umask according to the desired file mode.  */
+	new_umask = ld->rpc_filemode ^ 0777;
+	old_umask = umask(new_umask);
 	if (bind(fd, (struct sockaddr *)&addr, sizeof(addr)))
 		err(1, "Binding rpc socket to '%s'", rpc_filename);
 	umask(old_umask);

lightningd/lightningd.c

@@ -78,7 +78,6 @@
 #include <signal.h>
 #include <sodium.h>
 #include <sys/resource.h>
-#include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
 
@@ -254,6 +253,16 @@ static struct lightningd *new_lightningd(const tal_t *ctx)
 	ld->initial_umask = umask(0);
 	umask(ld->initial_umask);
 
+	/*~ This is the mode of the created JSON-RPC socket file, in
+	 * traditional Unix octal. 0600 means only the user that ran
+	 * lightningd can invoke RPC on it. Changing it to 0660 may
+	 * be sensible if you run lightningd in its own system user,
+	 * and just let specific users (add the group of the
+	 * lightningd runner as an ancillary group) access its
+	 * RPC. Can be overridden with `--rpc-file-mode`.
+	 */
+	ld->rpc_filemode = 0600;
+
 	return ld;
 }
 

lightningd/lightningd.h

@@ -10,6 +10,7 @@
 #include <lightningd/htlc_set.h>
 #include <lightningd/plugin.h>
 #include <stdio.h>
+#include <sys/stat.h>
 #include <wallet/txfilter.h>
 #include <wallet/wallet.h>
 
@@ -91,6 +92,8 @@ struct lightningd {
 
 	/* Location of the RPC socket. */
 	char *rpc_filename;
+	/* Mode of the RPC filename. */
+	mode_t rpc_filemode;
 
 	/* The root of the jsonrpc interface. Can be shut down
 	 * separately from the rest of the daemon to allow a clean

lightningd/options.c

@@ -105,6 +105,30 @@ static char *opt_set_s32(const char *arg, s32 *u)
 	return NULL;
 }
 
+static char *opt_set_mode(const char *arg, mode_t *m)
+{
+	char *endp;
+	long l;
+
+	assert(arg != NULL);
+
+	/* Ensure length, and starts with 0.  */
+	if (strlen(arg) != 4 || arg[0] != '0')
+		return tal_fmt(NULL, "'%s' is not a file mode", arg);
+
+	/* strtol, manpage, yech.  */
+	errno = 0;
+	l = strtol(arg, &endp, 8); /* Octal.  */
+	if (errno || *endp)
+		return tal_fmt(NULL, "'%s' is not a file mode", arg);
+	*m = l;
+	/* Range check not needed, previous strlen checks ensures only
+	 * 9-bit, which fits mode_t (unless your Unix is seriously borked).
+	 */
+
+	return NULL;
+}
+
 static char *opt_add_addr_withtype(const char *arg,
 				   struct lightningd *ld,
 				   enum addr_listen_announce ala,
@@ -225,6 +249,11 @@ static void opt_show_s32(char buf[OPT_SHOW_LEN], const s32 *u)
 	snprintf(buf, OPT_SHOW_LEN, "%"PRIi32, *u);
 }
 
+static void opt_show_mode(char buf[OPT_SHOW_LEN], const mode_t *m)
+{
+	snprintf(buf, OPT_SHOW_LEN, "\"%04o\"", (int) *m);
+}
+
 static char *opt_set_rgb(const char *arg, struct lightningd *ld)
 {
 	assert(arg != NULL);
@@ -842,6 +871,11 @@ static void register_opts(struct lightningd *ld)
 	                   "Set the password to encrypt hsm_secret with. If no password is passed through command line, "
 	                   "you will be prompted to enter it.");
 
+	opt_register_arg("--rpc-file-mode", &opt_set_mode, &opt_show_mode,
+			 &ld->rpc_filemode,
+			 "Set the file mode (permissions) for the "
+			 "JSON-RPC socket");
+
 	opt_register_logging(ld);
 	opt_register_version();