ask-password: don't show wall message on ttys we are already running a tty agent on

src/shutdownd.c

@@ -108,7 +108,7 @@ static void warn_wall(usec_t n, struct shutdownd_command *c) {
                 return;
 
         if (c->wall_message[0])
-                utmp_wall(c->wall_message);
+                utmp_wall(c->wall_message, NULL);
         else {
                 char date[FORMAT_TIMESTAMP_MAX];
                 const char* prefix;
@@ -126,7 +126,7 @@ static void warn_wall(usec_t n, struct shutdownd_command *c) {
                 if (asprintf(&l, "%s%s!", prefix, format_timestamp(date, sizeof(date), c->elapse)) < 0)
                         log_error("Failed to allocate wall message");
                 else {
-                        utmp_wall(l);
+                        utmp_wall(l, NULL);
                         free(l);
                 }
         }

src/systemctl.c

@@ -258,7 +258,7 @@ static void warn_wall(enum action action) {
                 }
 
                 if (*p) {
-                        utmp_wall(p);
+                        utmp_wall(p, NULL);
                         free(p);
                         return;
                 }
@@ -269,7 +269,7 @@ static void warn_wall(enum action action) {
         if (!table[action])
                 return;
 
-        utmp_wall(table[action]);
+        utmp_wall(table[action], NULL);
 }
 
 struct unit_info {

src/tty-ask-password-agent.c

@@ -30,6 +30,7 @@
 #include <unistd.h>
 #include <getopt.h>
 #include <sys/signalfd.h>
+#include <fcntl.h>
 
 #include "util.h"
 #include "conf-parser.h"
@@ -335,6 +336,55 @@ finish:
         return r;
 }
 
+static int tty_block(void) {
+        char *p;
+        const char *t;
+        int fd;
+
+        if (!(t = ttyname(STDIN_FILENO)))
+                return -errno;
+
+        if (asprintf(&p, "/dev/.systemd/ask-password-block/%s", file_name_from_path(t)) < 0)
+                return -ENOMEM;
+
+        mkdir_parents(p, 0700);
+        mkfifo(p, 0600);
+
+        fd = open(p, O_RDONLY|O_CLOEXEC|O_NONBLOCK|O_NOCTTY);
+        free(p);
+
+        if (fd < 0)
+                return -errno;
+
+        return fd;
+}
+
+static bool tty_match(const char *path) {
+        int fd;
+        char *p;
+
+        /* We use named pipes to ensure that wall messages suggesting
+         * password entry are not printed over password prompts
+         * already shown. We use the fact here that opening a pipe in
+         * non-blocking mode for write-only will succeed only if
+         * there's some writer behind it. Using pipes has the
+         * advantage that the block will automatically go away if the
+         * process dies. */
+
+        if (asprintf(&p, "/dev/.systemd/ask-password-block/%s", file_name_from_path(path)) < 0)
+                return true;
+
+        fd = open(p, O_WRONLY|O_CLOEXEC|O_NONBLOCK|O_NOCTTY);
+        free(p);
+
+        if (fd < 0)
+                return true;
+
+        /* What, we managed to open the pipe? Then this tty is filtered. */
+        close_nointr_nofail(fd);
+        return false;
+}
+
 static int show_passwords(void) {
         DIR *d;
         struct dirent *de;
@@ -375,7 +425,7 @@ static int show_passwords(void) {
                 free(p);
 
                 if (wall) {
-                        utmp_wall(wall);
+                        utmp_wall(wall, tty_match);
                         free(wall);
                 }
         }
@@ -394,11 +444,13 @@ static int watch_passwords(void) {
                 _FD_MAX
         };
 
-        int notify = -1, signal_fd = -1;
+        int notify = -1, signal_fd = -1, tty_block_fd = -1;
         struct pollfd pollfd[_FD_MAX];
         sigset_t mask;
         int r;
 
+        tty_block_fd = tty_block();
+
         mkdir_p("/dev/.systemd/ask-password", 0755);
 
         if ((notify = inotify_init1(IN_CLOEXEC)) < 0) {
@@ -456,6 +508,9 @@ finish:
         if (signal_fd >= 0)
                 close_nointr_nofail(signal_fd);
 
+        if (tty_block_fd >= 0)
+                close_nointr_nofail(tty_block_fd);
+
         return r;
 }
 

src/utmp-wtmp.c

@@ -358,7 +358,7 @@ finish:
         return r;
 }
 
-int utmp_wall(const char *message) {
+int utmp_wall(const char *message, bool (*match_tty)(const char *tty)) {
         struct utmpx *u;
         char date[FORMAT_TIMESTAMP_MAX];
         char *text = NULL, *hn = NULL, *un = NULL, *tty = NULL;
@@ -407,8 +407,9 @@ int utmp_wall(const char *message) {
                         path = buf;
                 }
 
-                if ((q = write_to_terminal(path, text)) < 0)
-                        r = q;
+                if (!match_tty || match_tty(path))
+                        if ((q = write_to_terminal(path, text)) < 0)
+                                r = q;
 
                 free(buf);
         }

src/utmp-wtmp.h

@@ -33,6 +33,6 @@ int utmp_put_runlevel(usec_t timestamp, int runlevel, int previous);
 int utmp_put_dead_process(const char *id, pid_t pid, int code, int status);
 int utmp_put_init_process(usec_t timestamp, const char *id, pid_t pid, pid_t sid, const char *line);
 
-int utmp_wall(const char *message);
+int utmp_wall(const char *message, bool (*match_tty)(const char *tty));
 
 #endif