From 2c864ba8fcf50246920d09feaa2b02f3a3dfd52c Mon Sep 17 00:00:00 2001
From: Karel Zak
Date: Mon, 27 May 2019 13:07:12 +0200
Subject: mesg: avoid 'ttyname failed: Success' message

The ttyname(3) can fail to access /dev/ path, and that will cause function
to fail without setting errno value with result of rather confusing error
message.  Lets start setting stdin permission via /proc when this happens as
a go-around, with hope kernel following symlink does not fail.  Ok, noted,
that hopes of symlink follow working are pretty slim.

Based on patch from Sami Kerola <kerolasa@iki.fi>.

Reference: https://github.com/lxc/lxd/issues/1724
Signed-off-by: Karel Zak <kzak@redhat.com>
---
 term-utils/Makemodule.am |  1 +
 term-utils/mesg.1        |  4 ++--
 term-utils/mesg.c        | 17 ++++++++++++++---
 3 files changed, 17 insertions(+), 5 deletions(-)

(limited to 'term-utils')

diff --git a/term-utils/Makemodule.am b/term-utils/Makemodule.am
index da05a722c..d0550f54a 100644
--- a/term-utils/Makemodule.am
+++ b/term-utils/Makemodule.am
@@ -54,6 +54,7 @@ endif
 
 if BUILD_MESG
 usrbin_exec_PROGRAMS += mesg
+mesg_LDADD = $(LDADD) libcommon.la
 dist_man_MANS += term-utils/mesg.1
 mesg_SOURCES = term-utils/mesg.c
 endif
diff --git a/term-utils/mesg.1 b/term-utils/mesg.1
index 15c834dd7..18e7c2451 100644
--- a/term-utils/mesg.1
+++ b/term-utils/mesg.1
@@ -58,8 +58,8 @@ should be executed in your login scripts.
 .PP
 The
 .B mesg
-utility silently exits with error status 2 if the current standard error output does
-not refer to the terminal.  In this case execute
+utility silently exits with error status 2 if not executed on terminal.  In this
+case execute
 .B mesg
 is pointless.  The command line option \fB\-\-verbose\fR forces
 mesg to print a warning in this situation.  This behaviour has been introduced
diff --git a/term-utils/mesg.c b/term-utils/mesg.c
index 57d53379f..56fb70094 100644
--- a/term-utils/mesg.c
+++ b/term-utils/mesg.c
@@ -59,6 +59,8 @@
 #include "nls.h"
 #include "c.h"
 #include "rpmatch.h"
+#include "ttyutils.h"
+#include "pathnames.h"
 
 /* exit codes */
 
@@ -90,6 +92,7 @@ int main(int argc, char *argv[])
 {
 	struct stat sb;
 	char *tty;
+	char ttybuf[sizeof(_PATH_PROC_FDDIR) + sizeof(stringify_value(INT_MAX))];
 	int ch, fd, verbose = FALSE, ret;
 
 	static const struct option longopts[] = {
@@ -121,13 +124,21 @@ int main(int argc, char *argv[])
 	argc -= optind;
 	argv += optind;
 
-	if (!isatty(STDERR_FILENO)) {
+	fd = get_terminal_stdfd();
+	if (fd < 0) {
 		if (verbose)
 			warnx(_("no tty"));
 		exit(MESG_EXIT_FAILURE);
 	}
-	if ((tty = ttyname(STDERR_FILENO)) == NULL)
-		err(MESG_EXIT_FAILURE, _("ttyname failed"));
+
+	tty = ttyname(fd);
+	if (!tty) {
+		snprintf(ttybuf, sizeof(ttybuf), "%s/%d", _PATH_PROC_FDDIR, fd);
+		tty = ttybuf;
+		if (verbose)
+			warnx(_("ttyname() failed, attempting to go around using: %s"), tty);
+	}
+
 	if ((fd = open(tty, O_RDONLY)) < 0)
 		err(MESG_EXIT_FAILURE, _("cannot open %s"), tty);
 	if (fstat(fd, &sb))
-- 
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