Re: SSHFS (SELinux) frustrations
On 01/16/2012 08:43 PM, Mr Dash Four wrote:
> 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)
I fixed this over the weekend, but thought to post a brief note of my
solution here for posterity just in case someone else stumbles across
the same problem.
As is usually the case with SELinux, I went for the "sledge-hammer"
solution after spending quite a number of hours banging my head
against the wall - I defined my own type (sshfs_root_t in my case) and
also constructed a separate pair of .te & .fc files responsible for
SSHFS implementation - sshfs.te & sshfs.fc. In the .fc file I defined
the context of the sshfs chroot system to be assigned to my
newly-created type - "/home/sftp-chroot(/.*)?". In sshfs.te I used the
manage_{dirs,files,sock_files,lnk_files}_pattern macros as well as
filetrans_pattern define from file_patterns.spt to grant the
appropriate level of access for this new context to the sftp_t and
sshd_t types.
It was also necessary to grant similar access for the new context to
syslogd_t in order to enable proper login inside the chroot. After
including this in my new policy all is well and everything works as it
should!
Admittedly, I could have used various tunables present in both ssh.te
and ftp.te policies to grant the appropriate access to
"user_home_dir_t" as was my initial intention, but this was giving a
wider-than-intended access to *all* directories defined by that
context - something I was not very happy with, hence I went for the
newly-defined context instead, so that I could limit the directories
as well as the domains to which to grant such access.
--
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The problem is
"sftp/chroot/SELinux" implementation is not working
correctly on F15. We added fixes to RHEL6/Rawhide which are going to be
backported. Also I am going to write a blog how to setup
sftp/chroot/SELinux solution which could help you with this issue.
Regards,
Miroslav