On Tue, Aug 10, 2010 at 09:24:31AM -0400, Steve Grubb wrote: > On Tuesday, August 10, 2010 08:46:28 am Neil Horman wrote: > > Specifically, my concerns are twofold: > > > > 1) struct format. By passing down a structure as your doing through an > > ioctl call, theres no way to extend/modify that structure easily for > > future use. For instance the integration of aead might I think requires a > > blocking factor to be sepcified, and entry for which you have no available > > field in your crypt_ops structure. If you extend the structure in a later > > release of this code, you create a potential incompatibility with user > > space because you are no longer guaranteed that the size of the crypt_op > > structure is the same, and you need to be prepared for a range of sizes to > > get passed down, at which point it becomes difficult to differentiate > > between older code thats properly formatted, and newer code thats > > legitimately broken. You might could add a version field to mitigate > > that, but it gets ugly pretty quickly. > > Yeah, this does call out for versioning. But the ioctls are just for crypto > parameter setup. Hopefully, that doesn't change too much since its just to > select an algorithm, possibly ask for a key to be wrapped and loaded, or ask > for a key to be created and exported. After setup, you just start using the > device. > > > > Thats why I had suggested the use of a netlink protocol to manage this kind > > of interface. There are other issue to manage there, but they're really > > not that big a deal, comparatively speaking, and that interface allows for > > the easy specification of arbitrary length data in a fashion that doesn't > > cause user space breakage when additional algorithms/apis are added. > > The problem with the netlink approach is that auditing is not as good because > netlink is an async protocol. The kernel can only use the credentials that > ride in the skb with the command since there is no guarantee the process has > not changed credentials by the time you get the packet. Adding more > credentials to the netlink headers is also not good. As it is now, the > auditing is synchronous with the syscall and we can get at more information > and reliably create the audit records called out by the protection profiles or > FIPS-140 level 2. > > -Steve I think thats pretty easy to serialize though. All you need to do is enforce a rule in the kernel that dictates any creditial changes to a given context must be serialized behind all previously submitted crypto operations. It might make life a bit tougher on the audit code, but netlink contains pid/sequence data in all messages so that audit can correlate requests and responses easily. Neil -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
