On Thu, 2007-08-02 at 23:14 -0400, David-Alexandre Davidson wrote:
> On fedora 7, lastest selinux strict policy.
>
> I have written a selinux module which go through a domain transition
> when executing a file on a nfs mount (labeled nfs_t)
> However the transition never occurs. and I get a : denied
> execute_no_trans on nfs_t files .
>
> In order to find the source of the problem I have taken a file with the
> exact same context outside of the nfs mount and the transition work fine.
>
> Here is the related part of my module:
>
> domain_auto_trans(custom_trans_t,nfs_t,i_custom_t);
> allow custom_trans_t nfs_t:file rx_file_perms;
> allow custom_trans_t nfs_t:dir r_dir_perms;
>
>
> Here are the details on the nfs share:
>
> file executed:
> -rwxrwxr-x vu20003 vg20003 system_u:object_r:nfs_t
> /home/usera/var/bin/testphp.app
>
> result:
> type=AVC msg=audit(1186108700.494:230294): avc: denied {
> execute_no_trans } for pid=5969 comm="custom-app" name="testphp.app"
> dev=0:18 ino=269058250 scontext=system_u:system_r:custom_trans_t:s0
> tcontext=system_u:object_r:nfs_t:s0 tclass=file
>
>
> Running the same program and executing an identical file outside the nfs
> share: (I labelled manually to match)
>
> file executed:
> -rwxrwxr-x vu20003 vg20003 system_u:object_r:nfs_t
> /testphp.app
>
> result:
> transition is made to context i_custom_t , nothing is audited
>
>
> Any idea what can cause this difference ? I don't believe this behavior
> is normal. By the way, if I allow the execute_no_trans on nfs_t, the
> file gets executed just fine but without the expected transition...
>
> Any help would be much appreciated !
If the filesystem is mounted nosuid, then SELinux domain transitions on
it are also disabled. Not as flexible as we might like, but a
conservative approach. Rationale is that if you didn't trust the
filesystem in the first place for suid binaries, then you likely don't
trust it for domain entrypoints either.
--
Stephen Smalley
National Security Agency
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