Re: [PATCH 01/11] keys-encrypted: add nvdimm key format type to encrypted keys

[Mimi Zohar <zohar@linux.ibm.com>]

On Tue, 2018-11-27 at 11:10 -0800, Dan Williams wrote:
> On Tue, Nov 27, 2018 at 10:24 AM Mimi Zohar <zohar@linux.ibm.com> wrote:
> >
> > On Tue, 2018-11-27 at 09:20 -0700, Dave Jiang wrote:
> > >
> > > On 11/27/18 12:20 AM, Dan Williams wrote:
> > > > On Fri, Nov 9, 2018 at 2:13 PM Dave Jiang <dave.jiang@intel.com> wrote:
> > > >>
> > > >> Adding nvdimm key format type to encrypted keys in order to limit the size
> > > >
> > > > s/Adding/Add an/
> > > >
> > > >> of the key to 32-bytes.
> > > >>
> > > >> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> > > >> ---
> > > >>  security/keys/encrypted-keys/encrypted.c |   29 ++++++++++++++++++++---------
> > > >>  1 file changed, 20 insertions(+), 9 deletions(-)
> > > >>
> > > >> diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c
> > > >> index d92cbf9687c3..182b4f136bdf 100644
> > > >> --- a/security/keys/encrypted-keys/encrypted.c
> > > >> +++ b/security/keys/encrypted-keys/encrypted.c
> > > >> @@ -45,6 +45,7 @@ static const char hmac_alg[] = "hmac(sha256)";
> > > >>  static const char blkcipher_alg[] = "cbc(aes)";
> > > >>  static const char key_format_default[] = "default";
> > > >>  static const char key_format_ecryptfs[] = "ecryptfs";
> > > >> +static const char key_format_nvdimm[] = "nvdimm";
> > > >>  static unsigned int ivsize;
> > > >>  static int blksize;
> > > >>
> > > >> @@ -54,6 +55,7 @@ static int blksize;
> > > >>  #define HASH_SIZE SHA256_DIGEST_SIZE
> > > >>  #define MAX_DATA_SIZE 4096
> > > >>  #define MIN_DATA_SIZE  20
> > > >> +#define KEY_NVDIMM_PAYLOAD_LEN 32
> > > >>
> > > >>  static struct crypto_shash *hash_tfm;
> > > >>
> > > >> @@ -62,12 +64,13 @@ enum {
> > > >>  };
> > > >>
> > > >>  enum {
> > > >> -       Opt_error = -1, Opt_default, Opt_ecryptfs
> > > >> +       Opt_error = -1, Opt_default, Opt_ecryptfs, Opt_nvdimm
> > > >>  };
> > > >>
> > > >>  static const match_table_t key_format_tokens = {
> > > >>         {Opt_default, "default"},
> > > >>         {Opt_ecryptfs, "ecryptfs"},
> > > >> +       {Opt_nvdimm, "nvdimm"},
> > > >>         {Opt_error, NULL}
> > > >>  };
> > > >>
> > > >> @@ -195,6 +198,7 @@ static int datablob_parse(char *datablob, const char **format,
> > > >>         key_format = match_token(p, key_format_tokens, args);
> > > >>         switch (key_format) {
> > > >>         case Opt_ecryptfs:
> > > >> +       case Opt_nvdimm:
> > > >>         case Opt_default:
> > > >>                 *format = p;
> > > >>                 *master_desc = strsep(&datablob, " \t");
> > > >> @@ -625,15 +629,22 @@ static struct encrypted_key_payload *encrypted_key_alloc(struct key *key,
> > > >>         format_len = (!format) ? strlen(key_format_default) : strlen(format);
> > > >>         decrypted_datalen = dlen;
> > > >>         payload_datalen = decrypted_datalen;
> > > >> -       if (format && !strcmp(format, key_format_ecryptfs)) {
> > > >> -               if (dlen != ECRYPTFS_MAX_KEY_BYTES) {
> > > >> -                       pr_err("encrypted_key: keylen for the ecryptfs format "
> > > >> -                              "must be equal to %d bytes\n",
> > > >> -                              ECRYPTFS_MAX_KEY_BYTES);
> > > >> -                       return ERR_PTR(-EINVAL);
> > > >> +       if (format) {
> > > >> +               if (!strcmp(format, key_format_ecryptfs)) {
> > > >> +                       if (dlen != ECRYPTFS_MAX_KEY_BYTES) {
> > > >> +                               pr_err("encrypted_key: keylen for the ecryptfs format must be equal to %d bytes\n",
> > > >> +                                       ECRYPTFS_MAX_KEY_BYTES);
> > > >> +                               return ERR_PTR(-EINVAL);
> > > >> +                       }
> > > >> +                       decrypted_datalen = ECRYPTFS_MAX_KEY_BYTES;
> > > >> +                       payload_datalen = sizeof(struct ecryptfs_auth_tok);
> > > >> +               } else if (!strcmp(format, key_format_nvdimm)) {
> > > >> +                       if (decrypted_datalen != KEY_NVDIMM_PAYLOAD_LEN) {
> > > >> +                               pr_err("encrypted_key: nvdimm key payload incorrect length: %d\n",
> > > >> +                                               decrypted_datalen);
> > > >> +                               return ERR_PTR(-EINVAL);
> > > >> +                       }
> > > >
> > > > I suspect this may not be the last key type that gets added, but I
> > > > wonder if we should instead create key-types based on the dlen size.
> > > > I.e. create a generic 32-byte key-type "enc32"? That way if another
> > > > 32-byte requirement key comes along we don't need to come touch this
> > > > routine again.
> > > >
> > >
> > > I'm ok with that if Mimi is.
> >
> > If the usage (eg. format: ecryptfs, nvdimm) limits the dlen size(s),
> > how will defining generic key-types help?  If there are no usage size
> > limitations, then there would be no usage specific definition.
> >
> > I must be missing something.
> 
> ...or I did a poor job of describing the problem. I'm just looking
> ahead to another potential encrypted-key use case, but instead of
> nvdimms this would be to lock / unlock persistent memory "namespace"
> objects. If it turns out the namespace key is just another 32-byte
> encrypted key should the encrypted-keys core grow support for a new
> "namespace" key type, should it reuse the "nvdimm" key type, or should
> we define a generic 32-byte payload-size-requirement key type?

Even with a generic length, there will be format (eg. ecryptfs,
nvdimm, namespace) specific code.  Otherwise you wouldn't be defining
a new format type.

switch(dlen) {
	case enc32:
		if (ecryptfs) goto fail;
		...
		break;
	case enc64:
		if (nvdimm || ns) goto fail;
		...
		break;
	default:
}

Mimi


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