** No longer affects: ubuntu-mate
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https://bugs.launchpad.net/bugs/1921655
Title:
lightdm-guest-session ICEauthority error
Status in lightdm package in Ubuntu:
Fix Released
Status in lightdm source package in Focal:
Fix Released
Status in lightdm source package in Groovy:
Fix Released
Status in lightdm source package in Hirsute:
Fix Released
Bug description:
[Impact]
If you enable the guest session feature on e.g. Ubuntu MATE, you are
met by an error message when trying to enter a guest session:
"Could not update file ICEauthority file /run/user/XXX/ICEauthority"
Even if it's not always a fatal error (the login may succeed after a
few minutes), the user experience is really bad, and you are inclined
to conclude that you are completely blocked from using the feature.
The proposed fix adds a rule to the lightdm-guest-session AppArmor
profile and prevents the error from happening.
[Test Plan]
On an updated Ubuntu MATE installation:
* Enable guest session
sudo sh -c 'printf "[Seat:*]\nallow-guest=true\n"
>/etc/lightdm/lightdm.conf.d/50-enable-guest.conf'
* Install lightdm from {focal,groovy}-proposed
* Reboot
You should now be able to enter a guest session without being stopped
by the ICEauthority error.
[Where problems could occur]
This one-liner is a harmless change.
The guest session is run in an unconfined mode since Ubuntu 16.10.
That's why the feature is disabled by default.
So if the additional rule would be wrong somehow (which I have no
reason to believe), it wouldn't break the AppArmor security layer for
the simple reason that it's already broken to begin with.
[Original description]
Hello I ran into trouble to start the lightdm-guest-session in linux
mint (cinnamon).
## How to reproduce:
- boot linux mint (20.02) or ubuntu mate (20.04) I haven't tested other
distros but I think others are also affected.
- enable guest user session
- try to login as guest user
## Error logs:
### Error Message:
` Could not update file ICEauthority file /run/user/XXX/ICEauthority`
### aa-notify:
```
Profile: /usr/lib/lightdm/lightdm-guest-session
Operation: open
Name: /proc/8125/uid_map
Denied: w
Logfile: /var/log/kern.log
Profile: /usr/lib/lightdm/lightdm-guest-session
Operation: open
Name: /proc/8125/setgroups
Denied: w
Logfile: /var/log/kern.log
Profile: /usr/lib/lightdm/lightdm-guest-session
Operation: open
Name: /proc/8125/gid_map
Denied: w
Logfile: /var/log/kern.log
Profile: /usr/lib/lightdm/lightdm-guest-session
Operation: open
Name: /proc/8624/fd/
Denied: r
Logfile: /var/log/kern.log
```
### dmesg:
```
[ 218.831289] audit: type=1400 audit(1616864450.287:76): apparmor="DENIED"
operation="sendmsg" profile="/usr/lib/lightdm/lightdm-guest-session"
name="/run/systemd/journal/dev-log" pid=3916 comm="cinnamon-sessio"
requested_mask="w" denied_mask="w" fsuid=999 ouid=0
[ 1157.263045] audit: type=1400 audit(1616865388.720:1084): apparmor="DENIED"
operation="open" profile="/usr/lib/lightdm/lightdm-guest-session"
name="/proc/9899/fd/" pid=9899 comm="gpg-agent" requested_mask="r"
denied_mask="r" fsuid=999 #ouid=0
[ 1157.899223] audit: type=1400 audit(1616865389.356:1085): apparmor="DENIED"
operation="open" profile="/usr/lib/lightdm/lightdm-guest-session"
name="/proc/1/cgroup" pid=9840 comm="cinnamon-sessio" requested_mask="r"
denied_mask="r" fsuid=999 ouid=0
[ 1157.899445] audit: type=1400 audit(1616865389.360:1086): apparmor="DENIED"
operation="sendmsg" profile="/usr/lib/lightdm/lightdm-guest-session"
name="/run/systemd/journal/dev-log" pid=9840 comm="cinnamon-sessio"
requested_mask="w" denied_mask="w" fsuid=999 ouid=0
[ 1157.903410] audit: type=1400 audit(1616865389.364:1087): apparmor="DENIED"
operation="link" profile="/usr/lib/lightdm/lightdm-guest-session"
name="/run/user/999/ICEauthority-l" pid=9840 comm="cinnamon-sessio"
requested_mask="l" denied_mask="l" fsuid=999 ouid=999
target="/run/user/999/ICEauthority-c"
```
## Solutions:
### bad but common work around
Solutions I found in different forums were to move lightdm-guest-session into
complain mode like this:
`aa-complain /usr/lib/lightdm/lightdm-guest-session`
### maybe better sollution:
My fix would be to add this to `/etc/apparmor.d/lightdm-guest-session`:
```
...
/usr/lib/lightdm/lightdm-guest-session {
...
owner /run/user/[0-9]*/ICEauthority-? l,`
...
}
```
I honestly have no clue about apparmor and I'm unsure where to post this but
I hope this maybe helps some other people in the future.
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