Re: Manual start of user@<uid>.service failed with permission denied

From: Mantas Mikulėnas <grawity@xxxxxxxxx>
Date: Tuesday, 12 December 2023 at 17:05
To: Christopher Wong <Christopher.Wong@xxxxxxxx>
Cc: Systemd <systemd-devel@xxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [systemd-devel] Manual start of user@<uid>.service failed with permission denied

That sounds like it's getting immediately unmounted (or maybe not being mounted at all despite the program doing so).

Hi Mantas,

 

I currently have the following flow:

 

1. No /run/user/1001 directory
2. systemctl start user@1001.service
3. systemd start user-runtime-dir@1001.service which ends successfully.
4. The directory /run/user/1001 exists now, but is empty, owned by root with mode 0700
5. I don’t have findmnt on my system, so I used mount, but /run/user/1001 is not listed.
6. systemd start user@1001.service which fails due to permission denied.

 

I can’t explain why the /run/user/1001 is owned by root after user-runtime-dir@1001.service successfully exited. I added some personal print in systemd code to ensure that the mount command returned success (r=0). Although, the mount was successful the command “mount” didn’t list it. In the list of mounts starting with /run I could only find these entries:

 

Dec 12 16:19:35 host mount[14500]: tmpfs on /run type tmpfs (rw,nosuid,nodev,mode=755)

Dec 12 16:19:35 host mount[14500]: tmpfs on /run/credentials type tmpfs (ro,nosuid,nodev,noexec,mode=755)

Dec 12 16:19:35 host mount[14500]: tmpfs on /run/systemd/incoming type tmpfs (ro,nosuid,nodev,mode=755)

 

If I do a chown of the directory in user@1001.service then it works

 

root@host:/run/user# ls -la 1001

drwx------    3 ida      root            80 Dec 12 16:19 .

drwxr-xr-x    3 root     root            60 Dec 12 16:19 ..

srw-rw-rw-    1 ida      ssh-user         0 Dec 12 16:19 bus

drwxr-xr-x    5 ida      ssh-user       140 Dec 12 16:19 systemd

 

The ”mount” command don’t list /run/user/1001 for the successful case either.

 

Best regards,

Christopher Wong

 

 

From: Mantas Mikulėnas <grawity@xxxxxxxxx>
Date: Monday, 11 December 2023 at 17:56
To: Christopher Wong <Christopher.Wong@xxxxxxxx>
Cc: Systemd <systemd-devel@xxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [systemd-devel] Manual start of user@<uid>.service failed with permission denied

On Mon, Dec 11, 2023, 17:28 Christopher Wong <Christopher.Wong@xxxxxxxx> wrote:

Hi Mantas,

 

I have added ExecStartPre to user@.service to run “id” and “ls -la”:

 

Dec 11 15:50:34 host systemd-user-runtime-dir[40287]: Will mount /run/user/1001 owned by 1001:118

Dec 11 15:50:34 host systemd-user-runtime-dir[40287]: Mounting tmpfs (tmpfs) on /run/user/1001 (MS_NOSUID|MS_NODEV "mode=0700,uid=1001,gid=118,size=99426304,nr_inodes=24274")...

Dec 11 15:50:34 host systemd[1]: Finished User Runtime Directory /run/user/1001.

Dec 11 15:50:34 host systemd[1]: Starting User Manager for UID 1001...

Dec 11 15:50:34 host id[40291]: uid=1001(ida) gid=118(ssh-users) groups=118(ssh-users),236(systemd-journal)

Dec 11 15:50:34 host ls[40293]: drwxr-xr-x    3 root     root            60 Dec 11 15:50 .

Dec 11 15:50:34 host ls[40293]: drwxr-xr-x   98 root     root          2120 Dec 11 15:30 ..

Dec 11 15:50:34 host ls[40293]: drwx------    2 root     root            40 Dec 11 15:50 1001

Dec 11 15:50:34 host systemd[40294]: systemd 254.7-2-g9edc143 running in user mode for user 1001/ida. (-PAM -AUDIT -SELINUX -APPARMOR +IMA -SMACK +SECCOMP +GCRYPT +GNUTLS +OPENSSL -ACL +BLKID +CURL -ELFUTILS -FIDO2 -IDN2 -IDN -IPTC +KMOD -LIBCRYPTSETUP +LIBFDISK -PCRE2 -PWQUALITY -P11KIT -QRENCODE -TPM2 +BZIP2 -LZ4 +XZ +ZLIB +ZSTD -BPF_FRAMEWORK -XKBCOMMON -UTMP -SYSVINIT default-hierarchy=unified)

 

The /run/user/1001 belongs to root with mode 0700. Should this belong to root?

No, it should be owned by UID 1001 (though still mode 0700).

Is it because I manually start user@1001.service as root?

Which user started the .service is usually not important, all services get a "fresh" environment that's fully described by the unit file.

 

So even if you did 'systemctl start' as root, the unit has User=%i so the instance parameter tells it which UID to run as, so will be running as UID 1001. Likewise user-runtime-dir@1001 will get the UID for the mount from its instance name (you can see that the "Mounting tmpfs" message has the correct information).

However, after user-runtime-dir@1001.service has finished it startup,  the user@1001.service is started as uid=1001 and therefore can’t create any directories under /run/user/1001. Resulting in user@1001.service failed to start.

 

If I add “ExecStartPre=+chown %i /run/user/%i” to user@.service then it works! But I am unsure if this is really the way fix this.

 

So far, it sounds like the directory is being created *by something else* before user-runtime-dir@ is even invoked.

 

Try adding the same "-/bin/ls -lad /run/user/%i" as both ExecStartPre and ExecStartPost of user-runtime-dir@ (and maybe even a findmnt). If the directory already exists during ExecStartPre, start looking for other services or cronjobs, or tmpfiles.d configs, or 'su' invocations, which may cause it to be created.

 

There might also be something that chowns it to root *after* it was created correctly. If you actually see the tmpfs mount in 'findmnt' or in 'mount', but it's owned by root despite having uid=1001 in its mount options, something has chowned it...or your tmpfs feature is broken.

 

If you don't see it in findmnt at all, even after user-runtime-dir has succeeded – either the mount failed quietly, or... something (like systemd itself) has quietly unmounted it.

 

 

Regarding the testing, I have done both restart of everything and manual, but the result is the same. Now that I have the “Environment=XDG_RUNTIME_DIR=/run/user/%i” I no longer need to do “systemctl set-environment …”

 

Thank you for taking your time!

 

Best regards,

Christopher Wong

 

 

From: Mantas Mikulėnas <grawity@xxxxxxxxx>
Date: Friday, 8 December 2023 at 21:53
To: Christopher Wong <Christopher.Wong@xxxxxxxx>
Cc: Systemd <systemd-devel@xxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [systemd-devel] Manual start of user@<uid>.service failed with permission denied

On Fri, Dec 8, 2023 at 6:53 PM Christopher Wong <Christopher.Wong@xxxxxxxx> wrote:

Hi Mantas,

 

I have from your suggestion done the following:

 

Putting the below in user@.service

 

[Service]

...

Environment=XDG_RUNTIME_DIR=/run/user/%i

Environment=SYSTEMD_LOG_LEVEL=debug

 

Putting the below in user-runtime-dir@.service

 

[Service]

...

Environment=SYSTEMD_LOG_LEVEL=debug

 

Then I have disabled the global set-log-level debug (if this is also required, please let me know).

 

Unlike set-environment that's not global, it only affects pid1.

 

 

What I can see from the logs is that user-runtime-dir@1001.service seems to be started and mount /run/user/1001, but addition creation of directory under this mount is getting permission denied.

 

Dec 08 17:33:29 host systemd[1]: Created slice User Slice of UID 1001.

Dec 08 17:33:29 host systemd[1]: Starting User Runtime Directory /run/user/1001...

Dec 08 17:33:29 host systemd-user-runtime-dir[36278]: Bus n/a: changing state UNSET -> OPENING

Dec 08 17:33:29 host systemd-user-runtime-dir[36278]: sd-bus: starting bus by connecting to /run/dbus/system_bus_socket...

Dec 08 17:33:29 host systemd-user-runtime-dir[36278]: Bus n/a: changing state OPENING -> AUTHENTICATING

Dec 08 17:33:29 host systemd-user-runtime-dir[36278]: Bus n/a: changing state AUTHENTICATING -> HELLO

Dec 08 17:33:29 host systemd-user-runtime-dir[36278]: Sent message type=method_call sender=n/a destination=org.freedesktop.DBus path=/org/freedesktop/DBus interface=org.freedesktop.DBus member=Hello cookie=1 reply_cookie=0 signature=n/a error-name=n/a error-message=n/a

Dec 08 17:33:29 host systemd-user-runtime-dir[36278]: Got message type=method_return sender=org.freedesktop.DBus destination=:1.2536 path=n/a interface=n/a member=n/a  cookie=1 reply_cookie=1 signature=s error-name=n/a error-message=n/a

Dec 08 17:33:29 host systemd-user-runtime-dir[36278]: Bus n/a: changing state HELLO -> RUNNING

Dec 08 17:33:29 host systemd-user-runtime-dir[36278]: Sent message type=method_call sender=n/a destination=org.freedesktop.login1 path=/org/freedesktop/login1 interface=org.freedesktop.DBus.Properties member=Get cookie=2 reply_cookie=0 signature=ss error-name=n/a error-message=n/a

Dec 08 17:33:29 host systemd-user-runtime-dir[36278]: Got message type=method_return sender=:1.323 destination=:1.2536 path=n/a interface=n/a member=n/a  cookie=15 reply_cookie=2 signature=v error-name=n/a error-message=n/a

Dec 08 17:33:29 host systemd-user-runtime-dir[36278]: Sent message type=method_call sender=n/a destination=org.freedesktop.login1 path=/org/freedesktop/login1 interface=org.freedesktop.DBus.Properties member=Get cookie=3 reply_cookie=0 signature=ss error-name=n/a error-message=n/a

Dec 08 17:33:29 host systemd-user-runtime-dir[36278]: Got message type=method_return sender=:1.323 destination=:1.2536 path=n/a interface=n/a member=n/a  cookie=16 reply_cookie=3 signature=v error-name=n/a error-message=n/a

Dec 08 17:33:29 host systemd-user-runtime-dir[36278]: Bus n/a: changing state RUNNING -> CLOSED

Dec 08 17:33:29 host systemd-user-runtime-dir[36278]: Will mount /run/user/1001 owned by 1001:118

Dec 08 17:33:29 host systemd-user-runtime-dir[36278]: Mounting tmpfs (tmpfs) on /run/user/1001 (MS_NOSUID|MS_NODEV "mode=0700,uid=1001,gid=118,size=99426304,nr_inodes=24274")...

Dec 08 17:33:29 host systemd[1]: Finished User Runtime Directory /run/user/1001.

Dec 08 17:33:29 host systemd[1]: Starting User Manager for UID 1001...

Dec 08 17:33:29 host systemd[36280]: systemd 254.7-2-g9edc143 running in user mode for user 1001/ida. (-PAM -AUDIT -SELINUX -APPARMOR +IMA -SMACK +SECCOMP +GCRYPT +GNUTLS +OPENSSL -ACL +BLKID +CURL -ELFUTILS -FIDO2 -IDN2 -IDN -IPTC +KMOD -LIBCRYPTSETUP +LIBFDISK -PCRE2 -PWQUALITY -P11KIT -QRENCODE -TPM2 +BZIP2 -LZ4 +XZ +ZLIB +ZSTD -BPF_FRAMEWORK -XKBCOMMON -UTMP -SYSVINIT default-hierarchy=unified)

Dec 08 17:33:29 host systemd[36280]: Failed to create '/run/user/1001/systemd/inaccessible', ignoring: Permission denied

Dec 08 17:33:29 host systemd[36280]: Failed to create '/run/user/1001/systemd/inaccessible/reg', ignoring: Permission denied

Dec 08 17:33:29 host systemd[36280]: Failed to create '/run/user/1001/systemd/inaccessible/dir', ignoring: Permission denied

Dec 08 17:33:29 host systemd[36280]: Failed to create '/run/user/1001/systemd/inaccessible/fifo', ignoring: Permission denied

Dec 08 17:33:29 host systemd[36280]: Failed to create '/run/user/1001/systemd/inaccessible/sock', ignoring: Permission denied

Dec 08 17:33:29 host systemd[36280]: Failed to create '/run/user/1001/systemd/inaccessible/chr', ignoring: Permission denied

Dec 08 17:33:29 host systemd[36280]: Failed to create '/run/user/1001/systemd/inaccessible/blk', ignoring: Permission denied

 

What's the ownership of /run/user/1001 and /run/user/1001/systemd after all of this?

 

Are you rebooting between tests or just manually starting it?

 

My current guess is that due to the earlier `systemctl set-environment`, some *other* thing that's running as root inherited the /run/user/1001 path and created root-owned directories there? That's the issue with setting global environment, it needs to be unset afterwards...

--

Mantas Mikulėnas