mesg: make group/all writability configurable

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/init/mesg.c b/init/mesg.c
index 676ca2e249e10c1013fd8a385268b02f5c3cfd1c..8489e621c1f36b31223664f17cc9ec5d54519b1a 100644 (file)
--- a/init/mesg.c
+++ b/init/mesg.c
@@ -7,16 +7,28 @@
  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  */
 
-//applet:IF_MESG(APPLET(mesg, BB_DIR_USR_BIN, BB_SUID_DROP))
-
-//kbuild:lib-$(CONFIG_MESG) += mesg.o
-
 //config:config MESG
 //config:      bool "mesg"
 //config:      default y
 //config:      help
 //config:        Mesg controls access to your terminal by others. It is typically
 //config:        used to allow or disallow other users to write to your terminal
+//config:
+//config:config FEATURE_MESG_ENABLE_ONLY_GROUP
+//config:      bool "Enable writing to tty only by group, not by everybody"
+//config:      default y
+//config:      depends on MESG
+//config:      help
+//config:        Usually, ttys are owned by group "tty", and "write" tool is
+//config:        setgid to this group. This way, "mesg y" only needs to enable
+//config:        "write by owning group" bit in tty mode.
+//config:
+//config:        If you set this option to N, "mesg y" will enable writing
+//config:        by anybody at all. This is not recommended.
+
+//applet:IF_MESG(APPLET(mesg, BB_DIR_USR_BIN, BB_SUID_DROP))
+
+//kbuild:lib-$(CONFIG_MESG) += mesg.o
 
 //usage:#define mesg_trivial_usage
 //usage:       "[y|n]"
@@ -27,7 +39,7 @@
 
 #include "libbb.h"
 
-#ifdef USE_TTY_GROUP
+#if ENABLE_FEATURE_MESG_ENABLE_ONLY_GROUP
 #define S_IWGRP_OR_S_IWOTH  S_IWGRP
 #else
 #define S_IWGRP_OR_S_IWOTH  (S_IWGRP | S_IWOTH)
@@ -37,30 +49,28 @@ int mesg_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int mesg_main(int argc UNUSED_PARAM, char **argv)
 {
        struct stat sb;
-       const char *tty;
+       mode_t m;
        char c = 0;
 
        argv++;
 
-       if (!argv[0]
-        || (!argv[1] && ((c = argv[0][0]) == 'y' || c == 'n'))
+       if (argv[0]
+        && (argv[1] || ((c = argv[0][0]) != 'y' && c != 'n'))
        ) {
-               tty = xmalloc_ttyname(STDERR_FILENO);
-               if (tty == NULL) {
-                       tty = "ttyname";
-               } else if (stat(tty, &sb) == 0) {
-                       mode_t m;
-                       if (c == 0) {
-                               puts((sb.st_mode & (S_IWGRP|S_IWOTH)) ? "is y" : "is n");
-                               return EXIT_SUCCESS;
-                       }
-                       m = (c == 'y') ? sb.st_mode | S_IWGRP_OR_S_IWOTH
-                                      : sb.st_mode & ~(S_IWGRP|S_IWOTH);
-                       if (chmod(tty, m) == 0) {
-                               return EXIT_SUCCESS;
-                       }
-               }
-               bb_simple_perror_msg_and_die(tty);
+               bb_show_usage();
+       }
+
+       if (!isatty(STDERR_FILENO))
+               bb_error_msg_and_die("not a tty");
+
+       xfstat(STDERR_FILENO, &sb, "stderr");
+       if (c == 0) {
+               puts((sb.st_mode & (S_IWGRP|S_IWOTH)) ? "is y" : "is n");
+               return EXIT_SUCCESS;
        }
-       bb_show_usage();
+       m = (c == 'y') ? sb.st_mode | S_IWGRP_OR_S_IWOTH
+                      : sb.st_mode & ~(S_IWGRP|S_IWOTH);
+       if (fchmod(STDERR_FILENO, m) != 0)
+               bb_perror_nomsg_and_die();
+       return EXIT_SUCCESS;
 }