write: query logind for list of users with tty (#2088)

util-linux · Mar 6, 2023 · 963eee4 · 963eee4
1 parent 4b81a80
commit 963eee4
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Showing 3 changed files with 109 additions and 3 deletions.
diff --git a/meson.build b/meson.build
@@ -2386,6 +2386,7 @@ exe = executable(
   write_sources,
   include_directories : includes,
   link_with : [lib_common],
+  dependencies : [lib_systemd],
   install_dir : usrbin_exec_dir,
   install : opt,
   build_by_default : opt)

diff --git a/term-utils/Makemodule.am b/term-utils/Makemodule.am
@@ -126,6 +126,10 @@ write_SOURCES = term-utils/write.c
 write_CFLAGS = $(SUID_CFLAGS) $(AM_CFLAGS)
 write_LDFLAGS = $(SUID_LDFLAGS) $(AM_LDFLAGS)
 write_LDADD = $(LDADD) libcommon.la
+if HAVE_SYSTEMD
+write_LDADD += $(SYSTEMD_LIBS)
+write_CFLAGS += $(SYSTEMD_CFLAGS)
+endif
 
 if USE_TTY_GROUP
 if MAKEINSTALL_DO_CHOWN

diff --git a/term-utils/write.c b/term-utils/write.c
@@ -57,7 +57,12 @@
 #include <sys/stat.h>
 #include <time.h>
 #include <unistd.h>
-#include <utmpx.h>
+
+#if defined(HAVE_LIBSYSTEMD) && HAVE_DECL_SD_SESSION_GET_USERNAME == 1
+# include <systemd/sd-login.h>
+#else
+# include <utmpx.h>
+#endif
 
 #include "c.h"
 #include "carefulputc.h"
@@ -129,8 +134,41 @@ static int check_tty(const char *tty, int *tty_writeable, time_t *tty_atime, int
  */
 static int check_utmp(const struct write_control *ctl)
 {
-	struct utmpx *u;
 	int res = 1;
+#if defined(HAVE_LIBSYSTEMD) && HAVE_DECL_SD_SESSION_GET_USERNAME == 1
+	char **sessions_list;
+        int sessions = sd_get_sessions(&sessions_list);
+        if (sessions < 0)
+                errx(EXIT_FAILURE, _("error getting sessions: %s"),
+                     strerror(-sessions));
+
+        for (int i = 0; i < sessions; i++) {
+                char *name, *tty;
+                int r;
+
+                if ((r = sd_session_get_username(sessions_list[i], &name)) < 0)
+                        errx(EXIT_FAILURE, _("get user name failed: %s"), strerror (-r));
+		if (sd_session_get_tty(sessions_list[i], &tty) < 0) {
+			free(name);
+			continue;
+		}
+
+		if  (strcmp(ctl->dst_login, name) == 0 &&
+		     strcmp(ctl->dst_tty_name, tty) == 0) {
+			free(name);
+			free(tty);
+			res = 0;
+			break;
+		}
+		free(name);
+		free(tty);
+	}
+	for (int i = 0; i < sessions; i++)
+		free(sessions_list[i]);
+	free(sessions_list);
+
+#else
+	struct utmpx *u;
 
 	utmpxname(_PATH_UTMP);
 	setutxent();
@@ -144,6 +182,7 @@ static int check_utmp(const struct write_control *ctl)
 	}
 
 	endutxent();
+#endif
 	return res;
 }
 
@@ -160,9 +199,70 @@ static int check_utmp(const struct write_control *ctl)
  */
 static void search_utmp(struct write_control *ctl)
 {
-	struct utmpx *u;
 	time_t best_atime = 0, tty_atime;
 	int num_ttys = 0, valid_ttys = 0, tty_writeable = 0, user_is_me = 0;
+
+#if defined(HAVE_LIBSYSTEMD) && HAVE_DECL_SD_SESSION_GET_USERNAME == 1
+	char path[256];
+	char **sessions_list;
+        int sessions = sd_get_sessions(&sessions_list);
+        if (sessions < 0)
+                errx(EXIT_FAILURE, _("error getting sessions: %s"),
+                     strerror(-sessions));
+
+        for (int i = 0; i < sessions; i++) {
+                char *name, *tty;
+                int r;
+
+                if ((r = sd_session_get_username(sessions_list[i], &name)) < 0)
+                        errx(EXIT_FAILURE, _("get user name failed: %s"), strerror (-r));
+
+		if  (strcmp(ctl->dst_login, name) != 0) {
+			free(name);
+			continue;
+		}
+
+		if (sd_session_get_tty(sessions_list[i], &tty) < 0) {
+			free(name);
+			continue;
+		}
+
+		num_ttys++;
+		snprintf(path, sizeof(path), "/dev/%s", tty);
+		if (check_tty(path, &tty_writeable, &tty_atime, 0)) {
+			/* bad term? skip */
+			free(name);
+			free(tty);
+			continue;
+		}
+		if (ctl->src_uid && !tty_writeable) {
+			/* skip ttys with msgs off */
+			free(name);
+			free(tty);
+			continue;
+		}
+		if (strcmp(tty, ctl->src_tty_name) == 0) {
+			user_is_me = 1;
+			free(name);
+			free(tty);
+			/* don't write to yourself */
+			continue;
+		}
+		valid_ttys++;
+		if (best_atime < tty_atime) {
+			best_atime = tty_atime;
+			free(ctl->dst_tty_path);
+			ctl->dst_tty_path = xstrdup(path);
+			ctl->dst_tty_name = ctl->dst_tty_path + 5;
+		}
+		free(name);
+		free(tty);
+	}
+	for (int i = 0; i < sessions; i++)
+		free(sessions_list[i]);
+	free(sessions_list);
+#else
+	struct utmpx *u;
 	char path[sizeof(u->ut_line) + 6];
 
 	utmpxname(_PATH_UTMP);
@@ -197,6 +297,7 @@ static void search_utmp(struct write_control *ctl)
 	}
 
 	endutxent();
+#endif
 	if (num_ttys == 0)
 		errx(EXIT_FAILURE, _("%s is not logged in"), ctl->dst_login);
 	if (valid_ttys == 0) {