From: Alejandro Colomar <alx@kernel.org>
Date: Fri, 3 Feb 2023 19:32:12 +0000 (+0100)
Subject: ttytype(): Fix race
X-Git-Tag: 4.14.0-rc1~186
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5da8388fc6009d2841459cf7e7e093d424c4213c;p=thirdparty%2Fshadow.git

ttytype(): Fix race

The intention of the code is just to not report an error message when
'typefile' doesn't exist.  If we call access(2) and then fopen(2),
there's a race.  It's not a huge problem, and the worst thing that can
happen is reporting an error when the file has been removed after
access(2).  It's not a problem, but we can fix the race and at the same
time clarify the intention of not warning about ENOENT and also remove
one syscall.  Seems like a win-win.

Suggested-by: Christian Göttsche <cgzones@googlemail.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
---

diff --git a/libmisc/ttytype.c b/libmisc/ttytype.c
index 9e5c4e896..a9fb0e860 100644
--- a/libmisc/ttytype.c
+++ b/libmisc/ttytype.c
@@ -34,13 +34,11 @@ void ttytype (const char *line)
 	if (NULL == typefile) {
 		return;
 	}
-	if (access (typefile, F_OK) != 0) {
-		return;
-	}
 
 	fp = fopen (typefile, "r");
 	if (NULL == fp) {
-		perror (typefile);
+		if (errno != ENOENT)
+			perror (typefile);
 		return;
 	}
 	while (fgets (buf, sizeof buf, fp) == buf) {