Bug 462231

You can just ignore this.

I have no idea of why it is happening.  Looks like sshd somehow has gotten seeing a key tab owned by crond_t.  I guess something in the kernel is looking through all of the keyrings context and generating these AVCs.

I can dontaudit or allow this,  But I think this could be a bug in the kernel.

Some api that sshd is calling is causing this avc to be triggered.

$ sudo grep 06f27a55-eba1-4903-be3b-372d535d92d6 /var/log/messages* | wc -l
19913

kind of hard to ignore.
hopefully I won't run out of diskspace before I get home :-)

I agree that it looks like a bug in the kernel keyring support - punting to David Howells for clarification.  SELinux labels keys based on their creator or based on the context the creator specified using setkeycreatecon(3).  I don't know why a key created by crond is being encountered by sshd on a lookup.

Possible workaround to silence the noise in the interim:
$ cat quietkey.te
policy_module(quietkey, 1.0)
require {
    type sshd_t;
    type crond_t;
}

dontaudit sshd_t crond_t:key search;
$ make -f /usr/share/selinux/devel/Makefile quietkey.pp
$ sudo semodule -i quietkey.pp

My guess is that the problem is not a kernel bug, but results from a feature mandated by Linus.

There are shared keyrings for each UID (user and user session keyrings), but these pick up the security label of whatever creates them and then are stuck with it, but such a keyring, once created, is automatically shared between all the processes that use that UID.

Does your /etc/pam.d/crond or /etc/pam.d/system-auth invoke pam_keyinit.so?

I am pretty sure they do.

crond doesn't, system-auth does

I just believe the kernel should not be reporting this as an AVC, it should be allowed.  If every keyring created for a user is going to require all domains that create keyrings to be able to search them, then there is little reason to deny.

Why isn't pam_keyinit using setkeycreatecon() to set the context for the key to something appropriate for the user whose keyring it is?

Also, if such sharing is mandated, how do we actually protect one program from misusing keys created by another program under the same uid?  Do we need per-context keyrings?

> Also, if such sharing is mandated, how do we actually protect one program
> from misusing keys created by another program under the same uid?  Do we
> need per-context keyrings?

The whole point of per-UID shared keyrings is that the keys in them are shared.  Misuse is something you might just have to live with.  If you don't want your keys to be misused, don't put them in the per-UID shared keyrings.

That said, any key that is in the per-UID shared keyring has all operations on it approved by SELinux.  That means a process can be restricted to only being able to find out the key ID of a key in one of these keyrings; the view, read, write, setattr, link and search attributes on a key can all be denied by SELinux, preventing a process from effectively doing anything with it.

There is, however, nothing to stop a process unlinking a specific key from those keyrings.  All that SELinux can see is that the keyring is being 'written'.  Also, there's nothing to stop a process finding the key ID by listing the keyring.  That's an all-or-nothing 'read' op on the keyring.  These two circumstances could be dealt with.

Another option is to make per-UID keyrings unavailable if SELINUX is enabled.  I'd need to check with Linus if he's happy to do this.  My original idea for how these might be used was for storing equivalent user identities, such as a SMB/CIFS/FAT/VFAT/NTFS user ID.  However, that's probably better stored in a session keyring.

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