Am Dienstag, 18. November 2014, 22:08:23 schrieb Herbert Xu: Hi Herbert, Steffen, > On Sun, Nov 16, 2014 at 03:24:25AM +0100, Stephan Mueller wrote: > > The AF_ALG interface allows normal cipher (hash, encrypt, decrypt). > > However, it does not allow user space to obtain the following generic > > > > information about the currently active cipher: > > * block size of the cipher > > > > * IV size of the cipher > > > > * for AEAD, the maximum authentication tag size > > > > The patch adds a getsockopt interface for the symmetric ciphers to > > answer such information requests from user space. > > > > The kernel crypto API function calls are used to obtain the real data. > > As all data are simple integer values, the getsockopt handler function > > uses put_user() to return the integer value to user space in the > > *optval parameter of getsockopt. > > > > Signed-off-by: Stephan Mueller <smueller@xxxxxxxxxx> > > We already have crypto_user so you should be extending that to > cover what's missing. After playing a bit with the interface, I think it falls short supporting AF_ALG in the following way: crypto_user cannot be applied to the currently active cipher that one has open with AF_ALG. For getting information, one has to call crypto_user with the cra_driver_name of a cipher. (Why is that limitation, btw (see crypto_report and the use of cru_driver_name?) When we open AF_ALG with the typical approach of simply a cra_name, you have no idea which cipher is selected. User space has no way to obtain the information on which particular cipher implementation is used with crypto_user. That means, to use crypto_user, we would first have to translate a cra_name into a cra_driver_name. Granted, any cra_driver_name for the given cra_name would work. But how would such a resolution be implemented? The only way would be via /proc/crypto. But that file does not contain all cipher / block chaining permutations. For example, ccm(aes) is not listed in /proc/crypto at all (even after using it via the kernel crypto API -- i.e. there is an accessible ccm(aes) implementation). Therefore, there is no way to resolve ccm(aes) to a cra_driver_name. Btw: is there an example that uses that interface? The ordering of data structures in the netlink message is not really clear from looking at the code. > > PS These paramters should not vary depending on the implementation, > if they do then one of the implementations must be buggy. > > Cheers, -- Ciao Stephan -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
