[CentOS] SELinux and rsh+xauth

Philippe Naudin philippe.naudin at supagro.inra.fr
Fri Jan 13 08:33:28 UTC 2012


Hello,

I have a strange (for me) problem with these two machines : 
- Client, a CentOS-5.7 workstation ;
- Server, a CentOS-6.2 headless, up-to-date server.

From Client, I want to use xauth on Server with the help of rsh (yes, I
know, ssh and all this sort of things... another time.)

When SELinux is in permissive mode on Server, all these commands
perform as expected : 
rsh Server /usr/bin/xauth info
rsh Server /usr/bin/xauth list
xauth nextract - Client:0.0 | rsh Server /usr/bin/xauth nmerge -

But when SELinux is in enforcing mode on Server, the commands fail with
this message : 
bash: /usr/bin/xauth: Permission denied

and /var/log/audit/audit.log shows the following errors :
type=SELINUX_ERR msg=audit(1326381080.364:610): security_compute_sid:  invalid context system_u:system_r:xauth_t:s0-s0:c0.c1023 for scontext=system_u:system_r:unconfined_t:s0-s0:c0.c1023 tcontext=system_u:object_r:xauth_exec_t:s0 tclass=process

type=AVC msg=audit(1326381080.364:610): avc:  denied  { write } for  pid=3487 comm="xauth" path="pipe:[21744]" dev=pipefs ino=21744 scontext=system_u:system_r:xauth_t:s0-s0:c0.c1023 tcontext=system_u:system_r:rshd_t:s0-s0:c0.c1023 tclass=fifo_file

type=AVC msg=audit(1326381080.369:611): avc:  denied  { getattr } for pid=3487 comm="xauth" path="socket:[21700]" dev=sockfs ino=21700 scontext=system_u:system_r:xauth_t:s0-s0:c0.c1023 tcontext=system_u:system_r:inetd_t:s0-s0:c0.c1023 tclass=tcp_socket

The output from audit2allow is here :
$ grep AVC /var/log/audit/audit.log | audit2allow
libsepol.context_from_record: invalid security context: "system_u:system_r:xauth_t:s0-s0:c0.c1023"
libsepol.context_from_record: could not create context structure
libsepol.context_from_string: could not create context structure
libsepol.sepol_context_to_sid: could not convert system_u:system_r:xauth_t:s0-s0:c0.c1023 to sid
(these 4 lines are repeated 2 times)

On Server, after creating a new authority file (with rsh again, while
Server is in permissive mode), I find :
$ ls -Z .Xauthority 
-rw-------. naudin biom system_u:object_r:xauth_home_t:s0 .Xauthority

I don't have this problem on a CentOS-5.7 server with the same
configuration.

Any idea (other than ssh) on how to solve it ?

Thanks,

-- 
Philippe Naudin



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