1 files changed, 187 insertions, 0 deletions
diff --git a/src/shared/wall.c b/src/shared/wall.c
new file mode 100644
index 0000000..d5900ef
--- /dev/null
+++ b/src/shared/wall.c
@@ -0,0 +1,187 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "sd-login.h"
+
+#include "errno-util.h"
+#include "fd-util.h"
+#include "hostname-util.h"
+#include "io-util.h"
+#include "path-util.h"
+#include "string-util.h"
+#include "terminal-util.h"
+#include "user-util.h"
+#include "utmp-wtmp.h"
+#include "wall.h"
+
+#if ENABLE_UTMP || ENABLE_LOGIND
+
+#define TIMEOUT_USEC (50 * USEC_PER_MSEC)
+
+static int write_to_terminal(const char *tty, const char *message) {
+        _cleanup_close_ int fd = -EBADF;
+
+        assert(tty);
+        assert(message);
+
+        fd = open(tty, O_WRONLY|O_NONBLOCK|O_NOCTTY|O_CLOEXEC);
+        if (fd < 0)
+                return -errno;
+        if (!isatty(fd))
+                return -ENOTTY;
+
+        return loop_write_full(fd, message, SIZE_MAX, TIMEOUT_USEC);
+}
+
+static int wall_utmp(
+        const char *message,
+        bool (*match_tty)(const char *tty, bool is_local, void *userdata),
+        void *userdata) {
+
+#if ENABLE_UTMP
+        _unused_ _cleanup_(utxent_cleanup) bool utmpx = false;
+        struct utmpx *u;
+        int r = 0;
+
+        assert(message);
+
+        /* libc's setutxent() unfortunately doesn't inform us about success, i.e. whether /var/run/utmp
+         * exists. Hence we have to check manually first. */
+        if (access(_PATH_UTMPX, F_OK) < 0) {
+                if (errno == ENOENT)
+                        return -ENOPROTOOPT;
+
+                return -errno;
+        }
+
+        utmpx = utxent_start();
+
+        while ((u = getutxent())) {
+                _cleanup_free_ char *p = NULL;
+                const char *tty_path;
+                bool is_local;
+
+                if (u->ut_type != USER_PROCESS || isempty(u->ut_user))
+                        continue;
+
+                /* This access is fine, because strlen("/dev/") < 32 (UT_LINESIZE) */
+                if (path_startswith(u->ut_line, "/dev/"))
+                        tty_path = u->ut_line;
+                else {
+                        if (asprintf(&p, "/dev/%.*s", (int) sizeof(u->ut_line), u->ut_line) < 0)
+                                return -ENOMEM;
+
+                        tty_path = p;
+                }
+
+                /* It seems that the address field is always set for remote logins. For local logins and
+                 * other local entries, we get [0,0,0,0]. */
+                is_local = eqzero(u->ut_addr_v6);
+
+                if (!match_tty || match_tty(tty_path, is_local, userdata))
+                        RET_GATHER(r, write_to_terminal(tty_path, message));
+        }
+
+        return r;
+
+#else
+        return -ENOPROTOOPT;
+#endif
+}
+
+static int wall_logind(
+        const char *message,
+        bool (*match_tty)(const char *tty, bool is_local, void *userdata),
+        void *userdata) {
+
+#if ENABLE_LOGIND
+        _cleanup_strv_free_ char **sessions = NULL;
+        int r;
+
+        assert(message);
+
+        r = sd_get_sessions(&sessions);
+        if (r <= 0)
+                return r;
+
+        r = 0;
+
+        STRV_FOREACH(s, sessions) {
+                _cleanup_free_ char *tty_path = NULL, *tty = NULL, *rhost = NULL;
+                bool is_local;
+                int q;
+
+                q = sd_session_get_tty(*s, &tty);
+                if (IN_SET(q, -ENXIO, -ENODATA))
+                        continue;
+                if (q < 0)
+                        return RET_GATHER(r, q);
+
+                tty_path = strjoin("/dev/", tty);
+                if (!tty_path)
+                        return -ENOMEM;
+
+                (void) sd_session_get_remote_host(*s, &rhost);
+                is_local = !rhost;
+
+                if (!match_tty || match_tty(tty_path, is_local, userdata))
+                        RET_GATHER(r, write_to_terminal(tty_path, message));
+        }
+
+        return r;
+
+#else
+        return -ENOPROTOOPT;
+#endif
+}
+
+int wall(
+        const char *message,
+        const char *username,
+        const char *origin_tty,
+        bool (*match_tty)(const char *tty, bool is_local, void *userdata),
+        void *userdata) {
+
+        _cleanup_free_ char *text = NULL, *hostname = NULL, *username_alloc = NULL, *stdin_tty = NULL;
+        int r;
+
+        assert(message);
+
+        hostname = gethostname_malloc();
+        if (!hostname)
+                return -ENOMEM;
+
+        if (!username) {
+                username_alloc = getlogname_malloc();
+                if (!username_alloc)
+                        return -ENOMEM;
+
+                username = username_alloc;
+        }
+
+        if (!origin_tty) {
+                (void) getttyname_harder(STDIN_FILENO, &stdin_tty);
+                origin_tty = stdin_tty;
+        }
+
+        if (asprintf(&text,
+                     "\r\n"
+                     "Broadcast message from %s@%s%s%s (%s):\r\n\r\n"
+                     "%s\r\n\r\n",
+                     username, hostname,
+                     origin_tty ? " on " : "", strempty(origin_tty),
+                     FORMAT_TIMESTAMP(now(CLOCK_REALTIME)),
+                     message) < 0)
+                return -ENOMEM;
+
+        r = wall_utmp(text, match_tty, userdata);
+        if (r == -ENOPROTOOPT)
+                r = wall_logind(text, match_tty, userdata);
+
+        return r == -ENOPROTOOPT ? 0 : r;
+}
+
+#endif