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Bug 170380 - RHEL3: login will attempt to run if it has no read/write access to its terminal
Summary: RHEL3: login will attempt to run if it has no read/write access to its terminal
Alias: None
Product: Red Hat Enterprise Linux 3
Classification: Red Hat
Component: util-linux
Version: 3.0
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Karel Zak
QA Contact: Ben Levenson
Whiteboard: RHEL3U7NAK
Depends On:
Blocks: RHEL3U8CanFix
TreeView+ depends on / blocked
Reported: 2005-10-11 08:21 UTC by Karel Zak
Modified: 2007-11-30 22:07 UTC (History)
0 users

Fixed In Version: RHBA-2006-0456
Doc Type: Bug Fix
Doc Text:
Clone Of:
Last Closed: 2006-07-20 14:45:59 UTC
Target Upstream Version:

Attachments (Terms of Use)

System ID Priority Status Summary Last Updated
Red Hat Product Errata RHBA-2006:0456 normal SHIPPED_LIVE util-linux and mount bug fix update 2006-07-19 18:48:00 UTC

Description Karel Zak 2005-10-11 08:21:02 UTC
+++ This bug was initially created as a clone of Bug #168436 +++

Description of problem:

If you manage to exec login with a userid other than root, and its input /
output directed to a terminal for which it does not have read/write access,
it will attempt to proceed and can potentially hang forever (see bug 168434).

This was a root cause of mgetty bug 167830, in which mgetty ran login for
a terminal that the userid did not have read/write access for (this problem
will be fixed in a future mgetty release) - but mgetty was doing:
    p = fork();
    if (p==0) 
       redirect stdin / stdout to terminal
       setuid() and setgid() to userid configured in login.config
       exec /bin/login 

If this happens, login could hang forever - it never checks if it has 
read / write access to its terminal before it does tcsetattr(0...) .

I propose making login do so , in check_ttyname(), where it already does 
an lstat:

login.c, @ line 280:
static void
check_ttyname(char *ttyn) {
	struct stat statbuf;

	if (lstat(ttyn, &statbuf)
	    || !S_ISCHR(statbuf.st_mode)
	    || (statbuf.st_nlink > 1 && strncmp(ttyn, "/dev/", 5))
+           || (access(ttyn,R_OK | W_OK) != 0))                                
		syslog(LOG_ERR, _("FATAL: bad tty"));

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
Exec login with stdin/stdout directed to a terminal for which it does not
have read+write access
Actual results:
login can hang forever or exit with unpredictable results

Expected results:
login should exit with an error

Additional info:
mgetty configuration to reproduce this available on request

-- Additional comment from on 2005-10-03 10:36 EST --
Thanks. Add to RHEL proposed list.

Comment 6 Bob Johnson 2006-04-11 16:32:37 UTC
This issue is on Red Hat Engineering's list of planned work items 
for the upcoming Red Hat Enterprise Linux 3.8 release.  Engineering 
resources have been assigned and barring unforeseen circumstances, Red 
Hat intends to include this item in the 3.8 release.

Comment 10 Red Hat Bugzilla 2006-07-20 14:45:59 UTC
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

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