Bug 1906157

Summary:	after su from root to a normal user mesg is unable to show current status
Product:	Red Hat Enterprise Linux 8	Reporter:	Michele Casaburo <mcasabur>
Component:	util-linux	Assignee:	Karel Zak <kzak>
Status:	CLOSED ERRATA	QA Contact:	Radka Brychtova <rskvaril>
Severity:	medium	Docs Contact:
Priority:	unspecified
Version:	8.3	CC:	alrodrig, jke, kzak, ngalvin, paygupta, veichler, vmishra
Target Milestone:	rc	Keywords:	Reopened
Target Release:	8.0
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	util-linux-2.32.1-28.el8	Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:
Clones:	2053536 (view as bug list)		Environment:
Last Closed:	2021-11-09 20:02:21 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	2053536

Description Michele Casaburo 2020-12-09 18:59:49 UTC

Description of problem:

After "su" from root to a normal user mesg is unable to retrieve current permissions as it cannot open the pty

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


How reproducible:


Steps to Reproduce:
1. clean RHEL 8.3 install
2. login as root
3. create a normal user
# useradd -m testuser
3. su to the user
# su testuser
4. run mesg
$ mesg

Actual results:
$ mesg
mesg: cannot open /dev/pts/0: Permission denied

Expected results:
$ mesg
is y

Additional info:

Comment 2 Karel Zak 2021-02-23 09:10:43 UTC

Sure, this is expected behavior. su(1) changes the user and group ID, but it still uses the original terminal with the original permissions.

Since v2.31 su(1) provides a new command-line option --pty to create a pseudo-terminal for the session, but it does not change permissions for the pty device. It seems like a disadvantage that I can fix in the upstream tree. 

Anyway, won't fix for RHEL8.

Comment 4 Karel Zak 2021-04-12 08:04:54 UTC

I have investigated the problem more closely and it seems we can fix it :-)

I thought the problem is only the relation between terminal and mesg(1) permissions, but the issue is that the new mesg(1) always tries to open the terminal device. It seems unnecessary. All we need is to call stat(2) in this case.

Sorry for the previous CLOSE/UPSTREAM, reopening.

Fixed also in the upstream tree by commit https://github.com/karelzak/util-linux/commit/c0246ce059503bbc078122a50d564ca36a66f348

Comment 15 errata-xmlrpc 2021-11-09 20:02:21 UTC

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (util-linux bug fix and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2021:4490

Comment 18 Karel Zak 2022-02-15 09:16:03 UTC

Please, see my answer for bug #2053536.