From: Jordi Sanfeliu <jordi@fibranet.cat>
To: newlib@sourceware.org
Subject: [PATCH] Fix getlogin() to check only stdin to get a valid tty
Date: Wed, 12 Jul 2023 19:33:58 +0200 [thread overview]
Message-ID: <1de3b3ee-7dd8-db16-6e17-365dbd9fde84@fibranet.cat> (raw)
Hello,
In my hobby OS [1] which uses Newlib C as its libc, I noticed that the
GNU command 'logname' does output nothing when it is redirected or pipe'd.
The current getlogin() implementation [2] forces the three primary file
descriptors (stdin, stdout and stderr) to be a valid tty before checking
the utmp file, otherwise it returns NULL. This makes impossible to
redirect (to a file or to a pipe), the output of a program that is using
this function because one of its file descriptors won't be a tty.
See:
# cat test.c
#include <stdio.h>
int main(void)
{
char *user;
if(user = getlogin()) {
printf("%s\n", user);
}
return 0;
}
# ./test
root
# ./test > xx
# cat xx
# ./test | cat
#
To fix this, I thought that only checking if stdin is a valid tty would
be enough.
Does this sound reasonable to you?
Thanks.
diff --git a/newlib/libc/unix/getlogin.c b/newlib/libc/unix/getlogin.c
index da4f47a95..e646bcb08 100644
--- a/newlib/libc/unix/getlogin.c
+++ b/newlib/libc/unix/getlogin.c
@@ -16,9 +16,7 @@ getlogin ()
extern char *ttyname ();
char *tty;
- if (((tty = ttyname (0)) == 0)
- || ((tty = ttyname (1)) == 0)
- || ((tty = ttyname (2)) == 0))
+ if ((tty = ttyname (0)) == 0)
return 0;
if ((utmp_fd = open (UTMP_FILE, O_RDONLY)) == -1)
1. https://www.fiwix.org
2.
https://sourceware.org/git/?p=newlib-cygwin.git;a=blob_plain;f=newlib/libc/unix/getlogin.c;hb=HEAD
--
Jordi Sanfeliu
FIBRANET Network Services Provider
https://www.fibranet.cat
next reply other threads:[~2023-07-12 17:34 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-12 17:33 Jordi Sanfeliu [this message]
2023-07-12 18:50 ` Torbjorn SVENSSON
2023-07-12 20:06 ` Brian Inglis
2023-07-13 16:26 ` Torbjorn SVENSSON
2023-07-13 8:06 ` Jordi Sanfeliu
2023-07-13 16:25 ` Torbjorn SVENSSON
2023-07-13 16:57 ` Jordi Sanfeliu
2023-07-13 19:01 ` Jeff Johnston
2023-07-17 7:54 ` Corinna Vinschen
2023-07-13 21:12 ` Stefan Tauner
2023-07-17 19:06 ` Jeff Johnston
2023-07-18 5:57 ` Jordi Sanfeliu
2023-07-18 7:08 ` Jordi Sanfeliu
2023-07-18 17:44 ` Jeff Johnston
2023-07-18 18:59 ` Jordi Sanfeliu
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