[Pkg-shadow-devel] acl, attr and selinux
nicolas.francois at centraliens.net
Mon Nov 21 21:56:32 UTC 2011
On Mon, Nov 21, 2011 at 01:23:31PM +0100, pvrabec at redhat.com wrote:
> On Thursday, November 17, 2011 11:53:32 PM Nicolas François wrote:
> > I have an issue with the following sequence:
> > * commonio_open
> > -> scontext is set to the /etc/shadow context
> > * No changes by the program
> > * commonio_close
> > -> goto success because there were no changes
> > -> setfscreatecon (NULL)
> > because we did not pass through getfscreatecon (&old_context)
> > I would propose the attached patch. Is this fine?
> > (I do not think there would really be issues because the shadow utils call
> > close() shortly before exit())
> > Other sequence with possible issue:
> > * no context associated to /etc/shadow
> > -> scontext set to NULL
> > * restricted file creation context set to the shadow util
> > => Can this happen?
> > => Should the file creation context be set to NULL before creating
> > /etc/<file>+
> > Question regarding SELinux: The overall goal of scontext is to set
> > the context of the temporary file /etc/shadow+ to the one of /etc/shadow.
> > Is there a way to set this context in advance even if /etc/shadow did not
> > exist (i.e. the context cannot be retrieved with fgetfilecon)?
> > (does getfilecon provide a context even if the file does not exist?)
> > Is it safe not to do it? Should the creation of /etc/shadow be forbidden
> > in some cases to let the admin create the file correctly (with the right
> > context)?
> Frankly, I don't understand how this code works. I mean selinux stuff in
> lib/commonio.c. That's why I put our selinux crew on the copy.
> fgetfilecon() in commonio_open() reads the SELinux context and store it into
> db->scontext. The stored context is freed in the end of commonio_open(). What
> was it used for?
The lines after "cleanup_entry:" are only executed in case of error.
db->scontext is always set when commonio_open() exits successfully (if
the database file already existed)
db->scontext is set to <file> context if <file> exists
create <file>+ with the db->scontext context if <file> existed
* save the fscreatecon
* set the fscreatecon to db->scontext
* save <file>+
* reset fscreatecon to the saved value
create <file>+ with the default fscreatecon if <file> did not exist
I think it is fine.
The questions remain:
1] Is it possible that:
* db->scontext is set to NULL because <file> has a default context
* getfscreatecon would return non NULL
(If I understand correctly, that should be the case if /etc/shadow
exists but was not assigned a context and useradd is labeled. What
should be the resulting context of /etc/shadow and the intermediate
2] Is there an API to retrieve the context that a file should have based
on its path, even if the file does not exist?
(or is there such concept in SELinux? Is restorecon the recommended
practice for such use case?)
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