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fedora-selinux: SSHFS (SELinux) frustrations

SSHFS (SELinux) frustrations

From: Mr Dash Four <mr.dash.four_at_nospam>
Date: Wed Jan 11 2012 - 15:45:07 GMT
To: selinux@lists.fedoraproject.org

I am trying to implement SSH FS on a shared DMZ box running SELinux (the
latest policy in FC15) and have the layout almost a carbon copy of what
is described in [1]. I have been frustrated by multiple failures, however.

The first thing I did after creating the directories is to set the
SELinux domain on these:

/home/sftp-chroot -d
gen_context(system_u:object_r:user_home_dir_t,s0)
/home/sftp-chroot/home(/.*)?
gen_context(system_u:object_r:user_home_dir_t,s0)
/home/sftp-chroot/dev -d
gen_context(system_u:object_r:device_t,s0)
/home/sftp-chroot/dev/log -s
gen_context(system_u:object_r:devlog_t,mls_systemhigh)

I've also altered the rsyslog in the way described in [1] so that a log
socket can be used inside chroot. I also altered the policy to enable
ssh home dirs access - gen_tunable(sftpd_enable_homedirs, true) in
ftp.te. On a side note, is there a way to do that in my policy
(sftpd_enable_homedirs -> on), without either altering ftp.te or using
setsebool? I've also noticed that /usr/libexec/openssh/sftp-server has
"bin_t" type - shouldn't that be "sftpd_t"?

When I try to use SSHFS with a dedicated using user account I used to
get a lot of AVC's, but I eventually got them reduced to just 2 - one
known (below), and one unknown:

type=AVC msg=audit(1326034699.037:356): avc: denied { create } for
pid=2713 comm="sshd" name="ltm-0.42.0.tar.bz2"
scontext=system_u:system_r:sshd_t:s0-s0:c0.c1023
tcontext=system_u:object_r:user_home_dir_t:s0 tclass=file
type=SYSCALL msg=audit(1326034699.037:356): arch=40000003 syscall=5
success=no exit=-13 a0=241388 a1=80c1 a2=81b4 a3=233284 items=0
ppid=2710 pid=2713 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0
sgid=0 fsgid=0 tty=(none) ses=30 comm="sshd" exe="/usr/sbin/sshd"
subj=system_u:system_r:sshd_t:s0-s0:c0.c1023 key=(null)

This happens when I try to copy a single file (ltm-0.42.0.tar.bz2 in
this case) to the SSHFS partition. So, in effect, even though I can look
at my newly-shared partition I can't do anything with it because of
SELinux. If I go into permisive mode - everything is fine (though I get
a lot of avcs, but that's to be expected).

The other error I get is when rsyslogd starts (at the very beginning
when the DMZ box starts) - I get "Permission denied" message and
rsyslogd cannot open that socket in /home/sftp-chroot/dev/log for some
reason - don't know why as it appears the context is properly set there!

Any help?

[1] -
http://blog.famzah.net/2011/02/03/secure-chroot-remote-file-access-via-sftp-and-ssh/
(Secure chroot() remote file access via SFTP and SSH)
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