mesg: fix multiple races

Signed-off-by: Sami Kerola <kerolasa@iki.fi>

diff --git a/term-utils/mesg.c b/term-utils/mesg.c
index 77d89c755ec77c4e8e038118ffbfef1c97924c77..4181a587426b1be53891f10ccd186c249d85188c 100644 (file)
--- a/term-utils/mesg.c
+++ b/term-utils/mesg.c
@@ -90,7 +90,7 @@ int main(int argc, char *argv[])
 {
        struct stat sb;
        char *tty;
-       int ch, verbose = FALSE;
+       int ch, fd, verbose = FALSE, ret;
 
        static const struct option longopts[] = {
                { "verbose",    no_argument,       0, 'v' },
@@ -123,11 +123,13 @@ int main(int argc, char *argv[])
 
        if ((tty = ttyname(STDERR_FILENO)) == NULL)
                err(MESG_EXIT_FAILURE, _("ttyname failed"));
-
-       if (stat(tty, &sb) < 0)
+       if ((fd = open(tty, O_RDONLY)) < 0)
+               err(MESG_EXIT_FAILURE, _("cannot open %s"), tty);
+       if (fstat(fd, &sb))
                err(MESG_EXIT_FAILURE, _("stat of %s failed"), tty);
 
        if (!*argv) {
+               close(fd);
                if (sb.st_mode & (S_IWGRP | S_IWOTH)) {
                        puts(_("is y"));
                        return IS_ALLOWED;
@@ -139,24 +141,28 @@ int main(int argc, char *argv[])
        switch (rpmatch(argv[0])) {
        case RPMATCH_YES:
 #ifdef USE_TTY_GROUP
-               if (chmod(tty, sb.st_mode | S_IWGRP) < 0)
+               if (fchmod(fd, sb.st_mode | S_IWGRP) < 0)
 #else
-               if (chmod(tty, sb.st_mode | S_IWGRP | S_IWOTH) < 0)
+               if (fchmod(fd, sb.st_mode | S_IWGRP | S_IWOTH) < 0)
 #endif
                        err(MESG_EXIT_FAILURE, _("change %s mode failed"), tty);
                if (verbose)
                        puts(_("write access to your terminal is allowed"));
-               return IS_ALLOWED;
+               ret = IS_ALLOWED;
+               break;
        case RPMATCH_NO:
-               if (chmod(tty, sb.st_mode & ~(S_IWGRP|S_IWOTH)) < 0)
+               if (fchmod(fd, sb.st_mode & ~(S_IWGRP|S_IWOTH)) < 0)
                         err(MESG_EXIT_FAILURE, _("change %s mode failed"), tty);
                if (verbose)
                        puts(_("write access to your terminal is denied"));
-               return IS_NOT_ALLOWED;
+               ret = IS_NOT_ALLOWED;
+               break;
        case RPMATCH_INVALID:
                warnx(_("invalid argument: %s"), argv[0]);
                usage(stderr);
         default:
                 abort();
        }
+       close(fd);
+       return ret;
 }