Description of problem:
The following AVC is generated if I try to login as an user_u. However, even if I allow the AVC I cannot login as user_u because of strange systemd error messages like

Failed to set security context (null) for /sys/fs: File exists

but no further AVCs are generated. If I set SELinux in permissive mode, I can login without any problems.
SELinux is preventing /usr/bin/gnome-shell from 'read' accesses on the file seat0.

*****  Plugin catchall (100. confidence) suggests  ***************************

If you believe that gnome-shell should be allowed read access on the seat0 file by default.
Then you should report this as a bug.
You can generate a local policy module to allow this access.
Do
allow this access for now by executing:
# grep gnome-shell /var/log/audit/audit.log | audit2allow -M mypol
# semodule -i mypol.pp

Additional Information:
Source Context                user_u:user_r:user_t:s0
Target Context                system_u:object_r:systemd_logind_var_run_t:s0
Target Objects                seat0 [ file ]
Source                        gnome-shell
Source Path                   /usr/bin/gnome-shell
Port                          <Unknown>
Host                          (removed)
Source RPM Packages           gnome-shell-3.6.2-6.fc18.x86_64
Target RPM Packages           
Policy RPM                    selinux-policy-3.11.1-73.fc18.noarch
Selinux Enabled               True
Policy Type                   targeted
Enforcing Mode                Permissive
Host Name                     (removed)
Platform                      Linux (removed) 3.7.2-204.fc18.x86_64 #1 SMP Wed
                              Jan 16 16:22:52 UTC 2013 x86_64 x86_64
Alert Count                   1
First Seen                    2013-01-26 08:06:23 CET
Last Seen                     2013-01-26 08:06:23 CET
Local ID                      d754b8cc-e5f7-4f40-b890-e04043b096f7

Raw Audit Messages
type=AVC msg=audit(1359183983.919:1566): avc:  denied  { read } for  pid=22932 comm="gnome-shell" name="seat0" dev="tmpfs" ino=427989 scontext=user_u:user_r:user_t:s0 tcontext=system_u:object_r:systemd_logind_var_run_t:s0 tclass=file


type=AVC msg=audit(1359183983.919:1566): avc:  denied  { open } for  pid=22932 comm="gnome-shell" path="/run/systemd/seats/seat0" dev="tmpfs" ino=427989 scontext=user_u:user_r:user_t:s0 tcontext=system_u:object_r:systemd_logind_var_run_t:s0 tclass=file


type=SYSCALL msg=audit(1359183983.919:1566): arch=x86_64 syscall=open success=yes exit=ENOSPC a0=24d6fc0 a1=80000 a2=1b6 a3=238 items=0 ppid=22719 pid=22932 auid=1001 uid=1001 gid=1001 euid=1001 suid=1001 fsuid=1001 egid=1001 sgid=1001 fsgid=1001 ses=22 tty=(none) comm=gnome-shell exe=/usr/bin/gnome-shell subj=user_u:user_r:user_t:s0 key=(null)

Hash: gnome-shell,user_t,systemd_logind_var_run_t,file,read

audit2allow

#============= user_t ==============
#!!!! This avc is allowed in the current policy

allow user_t systemd_logind_var_run_t:file { read open };

audit2allow -R

#============= user_t ==============
#!!!! This avc is allowed in the current policy

allow user_t systemd_logind_var_run_t:file { read open };


Additional info:
hashmarkername: setroubleshoot
kernel:         3.7.2-204.fc18.x86_64
type:           libreport