[systemd-devel] Manual start of user@<uid>.service failed with permission denied

Tue Dec 12 15:34:36 UTC 2023

Hi Mantas,

I currently have the following flow:

  1.  No /run/user/1001 directory
  2.  systemctl start user at 1001.service<mailto:user at 1001.service>
  3.  systemd start user-runtime-dir at 1001.service<mailto:user-runtime-dir at 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 at 1001.service<mailto:user at 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 at 1001.service<mailto:user-runtime-dir at 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 at 1001.service<mailto:user at 1001.service> then it works

root at 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 at gmail.com>
Date: Monday, 11 December 2023 at 17:56
To: Christopher Wong <Christopher.Wong at axis.com>
Cc: Systemd <systemd-devel at lists.freedesktop.org>
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 at axis.com<mailto:Christopher.Wong at axis.com>> wrote:
Hi Mantas,

I have added ExecStartPre to user at .service<mailto:user at .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 at 1001.service<mailto:user at 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 at 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 at 1001.service<mailto:user-runtime-dir at 1001.service> has finished it startup,  the user at 1001.service<mailto:user at 1001.service> is started as uid=1001 and therefore can’t create any directories under /run/user/1001. Resulting in user at 1001.service<mailto:user at 1001.service> failed to start.

If I add “ExecStartPre=+chown %i /run/user/%i” to user at .service<mailto:user at .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 at gmail.com<mailto:grawity at gmail.com>>
Date: Friday, 8 December 2023 at 21:53
To: Christopher Wong <Christopher.Wong at axis.com<mailto:Christopher.Wong at axis.com>>
Cc: Systemd <systemd-devel at lists.freedesktop.org<mailto:systemd-devel at lists.freedesktop.org>>
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 at axis.com<mailto:Christopher.Wong at axis.com>> wrote:
Hi Mantas,

I have from your suggestion done the following:

Putting the below in user at .service

[Service]
...
Environment=XDG_RUNTIME_DIR=/run/user/%i
Environment=SYSTEMD_LOG_LEVEL=debug

Putting the below in user-runtime-dir at .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 at 1001.service<mailto:user-runtime-dir at 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
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