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):
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: cannot open /dev/pts/0: Permission denied
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.
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
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.
Please, see my answer for bug #2053536.