On 2/14/20 12:21 PM, Daniel Colascione wrote:
On Fri, Feb 14, 2020 at 8:38 AM Stephen Smalley <sds@xxxxxxxxxxxxx> wrote:
That's assuming you are ok with having to define these type_transition
rules for the userfaultfd case instead of having your own separate
security class. Wondering how many different anon inode names/classes
there are in the kernel today and how much they change over time; for a
small, relatively stable set, separate classes might be ok; for a large,
dynamic set, type transitions should scale better.
I think we can get away without a class per anonymous-inode-type. I do
wonder whether we need a class for all anonymous inodes, though: if we
just give them the file class and use the anon inode type name for the
type_transition rule, isn't it possible that the type_transition rule
might also fire for plain files with the same names in the last path
component and the same originating sid? (Maybe I'm not understanding
type_transition rules properly.) Using a class to encompass all
anonymous inodes would address this problem (assuming the problem
exists in the first place).
It shouldn't fire for non-anon inodes because on a (non-anon) file
creation, security_transition_sid() is passed the parent directory SID
as the second argument and we only assign task SIDs to /proc/pid
directories, which don't support (userspace) file creation anyway.
However, in the absence of a matching type_transition rule, we'll end up
defaulting to the task SID on the anon inode, and without a separate
class we won't be able to distinguish it from a /proc/pid inode. So
that might justify a separate anoninode or similar class.
This however reminded me that for the context_inode case, we not only
want to inherit the SID but also the sclass from the context_inode.
That is so that anon inodes created via device node ioctls inherit the
same SID/class pair as the device node and a single allowx rule can
govern all ioctl commands on that device.
