From 21156da2fed163310dcff8aa5d16a1e4870e8007 Mon Sep 17 00:00:00 2001

From: Alexey Gladkov <legion@altlinux.org>

Date: Thu, 14 May 2020 15:26:19 +0300

Subject: OWL: write(1) improvements

* Add prompt/prefix with usernames.

* Disable locale support in write(1) entirely for security reasons

  (dangerous printf formats, control characters, anonymous messages).

Signed-off-by: Alexey Gladkov <legion@altlinux.org>

---

 util-linux/term-utils/write.c | 41 +++++++++++++++++++++++++++++------

 1 file changed, 34 insertions(+), 7 deletions(-)

diff --git a/util-linux/term-utils/write.c b/util-linux/term-utils/write.c

index 50f18dcd..874ec64f 100644

--- a/util-linux/term-utils/write.c

+++ b/util-linux/term-utils/write.c

@@ -50,6 +50,7 @@

 #include <paths.h>

 #include <pwd.h>

 #include <signal.h>

+#include <limits.h>

 #include <stdio.h>

 #include <stdlib.h>

 #include <string.h>

@@ -243,21 +244,39 @@ static void write_line(char *s)

  */

 static void do_write(const struct write_control *ctl)

 {

-	char *login, *pwuid;

+	char *login, *pwuid, *prompt, *prefix;

 	struct passwd *pwd;

 	time_t now;

 	struct tm *tm;

-	char *host, line[512];

+	char *host, line[BUFSIZ - 1];

 	struct sigaction sigact;

 	/* Determine our login name(s) before the we reopen() stdout */

 	if ((pwd = getpwuid(ctl->src_uid)) != NULL)

 		pwuid = pwd->pw_name;

-	else

-		pwuid = "???";

+	else {

+		perror("getpwuid");

+		pwuid = alloca(4 + sizeof(ctl->src_uid) * CHAR_BIT / 3 + 1 + 1);

+		if (!pwuid)

+			exit(1);

+		sprintf(pwuid, "UID %u", ctl->src_uid);

+	}

 	if ((login = getlogin()) == NULL)

 		login = pwuid;

+	if (isatty(STDIN_FILENO)) {

+		prompt = alloca(strlen(ctl->dst_login) + 2 + 1);

+		if (!prompt)

+			exit(1);

+		sprintf(prompt, "%s> ", ctl->dst_login);

+	} else

+		prompt = "";

+

+	prefix = alloca(strlen(login) + 3 + 1);

+	if (!prefix)

+		exit(1);

+	sprintf(prefix, "<%s> ", login);

+

 	if ((freopen(ctl->dst_tty_path, "w", stdout)) == NULL)

 		err(EXIT_FAILURE, "%s", ctl->dst_tty_path);

@@ -286,12 +305,21 @@ static void do_write(const struct write_control *ctl)

 	free(host);

 	printf("\r\n");

+	fprintf(stderr, "%s", prompt);

 	while (fgets(line, sizeof(line), stdin) != NULL) {

 		if (signal_received)

 			break;

+		write_line(prefix);

 		write_line(line);

+		if (!strchr(line, '\n')) {

+			write_line("\n");

+			fputc('\n', stderr);

+		}

+		fprintf(stderr, "%s", prompt);

 	}

 	printf("EOF\r\n");

+	if (isatty(STDIN_FILENO))

+		fputc('\n', stderr);

 }

 int main(int argc, char **argv)

@@ -305,9 +333,8 @@ int main(int argc, char **argv)

 		{NULL, 0, NULL, 0}

 	};

-	setlocale(LC_ALL, "");

-	bindtextdomain(PACKAGE, LOCALEDIR);

-	textdomain(PACKAGE);

+	unsetenv("TZ");

+	setlocale(LC_CTYPE, "");

 	close_stdout_atexit();

 	while ((c = getopt_long(argc, argv, "Vh", longopts, NULL)) != -1)

-- 

2.25.4