On 03/14/2018 10:27 AM, Serge E. Hallyn wrote:
Quoting Stefan Berger (stefanb@xxxxxxxxxxxxxxxxxx):
On 03/12/2018 03:29 PM, Serge E. Hallyn wrote:
Quoting Mimi Zohar (zohar@xxxxxxxxxxxxxxxxxx):
Files on FUSE can change at any point in time without IMA being able
to detect it. The file data read for the file signature verification
could be totally different from what is subsequently read, making the
signature verification useless.
FUSE can be mounted by unprivileged users either today with fusermount
installed with setuid, or soon with the upcoming patches to allow FUSE
mounts in a non-init user namespace.
This patch sets the SB_I_IMA_UNVERIFIABLE_SIGNATURE flag and when
appropriate sets the SB_I_UNTRUSTED_MOUNTER flag.
Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
Cc: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Dongsu Park <dongsu@xxxxxxxxxx>
Cc: Alban Crequy <alban@xxxxxxxxxx>
Cc: "Serge E. Hallyn" <serge@xxxxxxxxxx>
Acked-by: Serge Hallyn <serge@xxxxxxxxxx>
Of course when IMA namespacing hits, you'll want to compare the
sb->s_user_ns to the (~handwaving~) user_ns owning the ima ns
right?
I suppose this would be the only way to enable 'trusted mounters'
within IMA namespaces. Maybe there could be an additional capability
gate that would allow one to be a 'trusted mounter' then?
Wouldn't CAP_SYS_ADMIN to the ima_ns->user_ns suffice?
I personally think CAP_INTEGRITY would make sense, but right
now CAP_SYS_ADMIN seems to suffice so it wouldn't make sense to
raise the bar there unless we raise it for all of IMA configuration.
So for IMA namespacing we may want to avoid CAP_SYS_ADMIN and introduce
one or more capabilities to:
- set security xattrs from inside the container (when building the
container for example, maybe also during runtime)
- access IMA's securityfs entries
(https://elixir.bootlin.com/linux/latest/source/security/integrity/ima/ima_fs.c#L391)
from inside the container for reading/writing the policy (during run-time)
- then possibly mounting a trusted filesystem via fuse
Stefan
-serge
