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

[Andrei Borzenkov]

On 11.12.2023 18:28, Christopher Wong 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.

> Is it because I manually start user at 1001.service<mailto:user at 1001.service> as root?

No.

> 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.

As clearly seen from logs, systemd-user-runtime-dir mounts tmpfs with 
option uid=1001 over /run/user/1001. Is it still a mounted filesystem 
when you check it? It sounds like you see mount point which indeed has 
permissions 700 and owner root, not mounted filesystem.

> 
> 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>
> Date: Friday, 8 December 2023 at 21:53
> 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 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