On Tue, 12 Jul 2016, Stephan Mueller wrote:
Hi Mat, David,
This patch is based on the cryptodev-2.6 tree with the patch
4693fc734d675c5518ea9bd4c9623db45bc37402 ("KEYS: Add placeholder
for KDF usage with DH") from Linus' tree added on top.
I am aware of the fact that the compat code is not present. This
patch is intended for review to verify that the user space
interface follows the general approach for the keys subsystem.
The patch to add KDF to the kernel crypto API will be appended to
this patch.
The patch for the keyutils user space extension will also be added.
Ciao
Stephan
---8<---
SP800-56A define the use of DH with key derivation function based on a
counter. The input to the KDF is defined as (DH shared secret || other
information). The value for the "other information" is to be provided by
the caller.
The KDF is provided by the kernel crypto API. The SP800-56A KDF is equal
to the SP800-108 counter KDF. However, the caller is allowed to specify
the KDF type that he wants to use to derive the key material allowing
the use of the other KDFs provided with the kernel crypto API.
As the KDF implements the proper truncation of the DH shared secret to
the requested size, this patch fills the caller buffer up to its size.
The patch is tested with a new test added to the keyutils user space
code which uses a CAVS test vector testing the compliance with
SP800-56A.
Signed-off-by: Stephan Mueller <smueller@xxxxxxxxxx>
---
include/uapi/linux/keyctl.h | 10 +++++
security/keys/Kconfig | 1 +
security/keys/dh.c | 98 ++++++++++++++++++++++++++++++++++++++++-----
security/keys/internal.h | 5 ++-
security/keys/keyctl.c | 2 +-
5 files changed, 103 insertions(+), 13 deletions(-)
Be sure to update Documentation/security/keys.txt once the interface is
settled on.
diff --git a/include/uapi/linux/keyctl.h b/include/uapi/linux/keyctl.h
index 86eddd6..cc4ce7c 100644
--- a/include/uapi/linux/keyctl.h
+++ b/include/uapi/linux/keyctl.h
@@ -68,4 +68,14 @@ struct keyctl_dh_params {
__s32 base;
};
+struct keyctl_kdf_params {
+#define KEYCTL_KDF_MAX_OUTPUTLEN 1024 /* max length of KDF output */
+#define KEYCTL_KDF_MAX_STRING_LEN 64 /* maximum length of strings */
I think these limits should be in the internal headers rather than uapi.
+ char *kdfname;
+ __u32 kdfnamelen;
As noted in the userspace patch, if kdfname is a null-terminated string
then kdfnamelen isn't needed.
+ char *otherinfo;
+ __u32 otherinfolen;
+ __u32 flags;
Looks like flags aren't used anywhere. Do you have a use planned? You
could add some spare capacity like the keyctl_pkey_* structs instead (see
https://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/commit/?h=keys-next&id=dd7e2ea418b4f8851a4eb976b9431fbc03d2ebaf
)
+};
+
#endif /* _LINUX_KEYCTL_H */
diff --git a/security/keys/Kconfig b/security/keys/Kconfig
index f826e87..56491fe 100644
--- a/security/keys/Kconfig
+++ b/security/keys/Kconfig
@@ -90,6 +90,7 @@ config KEY_DH_OPERATIONS
bool "Diffie-Hellman operations on retained keys"
depends on KEYS
select MPILIB
+ select CRYPTO_KDF
help
This option provides support for calculating Diffie-Hellman
public keys and shared secrets using values stored as keys
diff --git a/security/keys/dh.c b/security/keys/dh.c
index 531ed2e..4c93969 100644
--- a/security/keys/dh.c
+++ b/security/keys/dh.c
@@ -77,14 +77,74 @@ error:
return ret;
}
+static int keyctl_dh_compute_kdf(struct keyctl_kdf_params *kdfcopy,
+ char __user *buffer, size_t buflen,
+ uint8_t *kbuf, size_t resultlen)
+{
Minor point: this function name made me think it was a replacement for
keyctl_dh_compute at first (like the userspace counterpart).
+ char kdfname[CRYPTO_MAX_ALG_NAME] = { 0 };
+ struct crypto_rng *tfm;
+ uint8_t *outbuf = NULL;
+ int ret;
+
+ BUILD_BUG_ON(CRYPTO_MAX_ALG_NAME != KEYCTL_KDF_MAX_STRING_LEN);
If this is a requirement, why define KEYCTL_KDF_MAX_STRING_LEN? Use
CRYPTO_MAX_ALG_NAME directly.
+ if (!kdfcopy->kdfnamelen)
+ return -EFAULT;
+ if (copy_from_user(&kdfname, kdfcopy->kdfname,
+ kdfcopy->kdfnamelen) != 0)
strndup_user works nicely for strings.
+ return -EFAULT;
+
It would be best to validate all of the userspace input before the DH
computation is done.
+ /*
+ * Concatenate otherinfo past DH shared secret -- the
+ * input to the KDF is (DH shared secret || otherinfo)
+ */
+ if (kdfcopy->otherinfo &&
+ copy_from_user(kbuf + resultlen, kdfcopy->otherinfo,
+ kdfcopy->otherinfolen)
+ != 0)
+ return -EFAULT;
+
+ tfm = crypto_alloc_rng(kdfname, 0, 0);
+ if (IS_ERR(tfm))
+ return PTR_ERR(tfm);
+
+#if 0
+ /* we do not support HMAC currently */
+ ret = crypto_rng_reset(tfm, xx, xxlen);
+ if (ret) {
+ crypto_free_rng(tfm);
+ goto error5;
+ }
+#endif
+
+ outbuf = kmalloc(buflen, GFP_KERNEL);
+ if (!outbuf) {
+ ret = -ENOMEM;
+ goto err;
+ }
+
+ ret = crypto_rng_generate(tfm, kbuf, resultlen + kdfcopy->otherinfolen,
+ outbuf, buflen);
+ if (ret)
+ goto err;
+
+ ret = buflen;
+ if (copy_to_user(buffer, outbuf, buflen) != 0)
+ ret = -EFAULT;
+
+err:
+ kzfree(outbuf);
+ crypto_free_rng(tfm);
+ return ret;
+}
long keyctl_dh_compute(struct keyctl_dh_params __user *params,
char __user *buffer, size_t buflen,
- void __user *reserved)
+ struct keyctl_kdf_params __user *kdf)
{
long ret;
MPI base, private, prime, result;
unsigned nbytes;
struct keyctl_dh_params pcopy;
+ struct keyctl_kdf_params kdfcopy;
uint8_t *kbuf;
ssize_t keylen;
size_t resultlen;
@@ -98,12 +158,24 @@ long keyctl_dh_compute(struct keyctl_dh_params __user *params,
goto out;
}
- if (reserved) {
- ret = -EINVAL;
- goto out;
+ if (kdf) {
+ if (copy_from_user(&kdfcopy, kdf, sizeof(kdfcopy)) != 0) {
+ ret = -EFAULT;
+ goto out;
+ }
+ if (buflen > KEYCTL_KDF_MAX_OUTPUTLEN ||
+ kdfcopy.otherinfolen > KEYCTL_KDF_MAX_STRING_LEN ||
+ kdfcopy.kdfnamelen > KEYCTL_KDF_MAX_STRING_LEN) {
+ ret = -EMSGSIZE;
+ goto out;
+ }
}
- keylen = mpi_from_key(pcopy.prime, buflen, &prime);
+ /*
+ * If the caller requests postprocessing with a KDF, allow an
+ * arbitrary output buffer size since the KDF ensures proper truncation.
+ */
+ keylen = mpi_from_key(pcopy.prime, kdf ? SIZE_MAX : buflen, &prime);
if (keylen < 0 || !prime) {
/* buflen == 0 may be used to query the required buffer size,
* which is the prime key length.
@@ -133,7 +205,8 @@ long keyctl_dh_compute(struct keyctl_dh_params __user *params,
goto error3;
}
- kbuf = kmalloc(resultlen, GFP_KERNEL);
+ kbuf = kmalloc(kdf ? (resultlen + kdfcopy.otherinfolen) : resultlen,
+ GFP_KERNEL);
if (!kbuf) {
ret = -ENOMEM;
goto error4;
@@ -147,12 +220,17 @@ long keyctl_dh_compute(struct keyctl_dh_params __user *params,
if (ret != 0)
goto error5;
- ret = nbytes;
- if (copy_to_user(buffer, kbuf, nbytes) != 0)
- ret = -EFAULT;
+ if (kdf) {
+ ret = keyctl_dh_compute_kdf(&kdfcopy, buffer, buflen,
+ kbuf, resultlen);
+ } else {
+ ret = nbytes;
+ if (copy_to_user(buffer, kbuf, nbytes) != 0)
+ ret = -EFAULT;
+ }
error5:
- kfree(kbuf);
+ kzfree(kbuf);
Thanks for adjusting this.
error4:
mpi_free(result);
error3:
diff --git a/security/keys/internal.h b/security/keys/internal.h
index a705a7d..35a8d11 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -259,12 +259,13 @@ static inline long keyctl_get_persistent(uid_t uid, key_serial_t destring)
#endif
#ifdef CONFIG_KEY_DH_OPERATIONS
+#include <crypto/rng.h>
extern long keyctl_dh_compute(struct keyctl_dh_params __user *, char __user *,
- size_t, void __user *);
+ size_t, struct keyctl_kdf_params __user *);
#else
static inline long keyctl_dh_compute(struct keyctl_dh_params __user *params,
char __user *buffer, size_t buflen,
- void __user *reserved)
+ struct keyctl_kdf_params __user *kdf)
{
return -EOPNOTSUPP;
}
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index d580ad0..b106898 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1689,7 +1689,7 @@ SYSCALL_DEFINE5(keyctl, int, option, unsigned long, arg2, unsigned long, arg3,
case KEYCTL_DH_COMPUTE:
return keyctl_dh_compute((struct keyctl_dh_params __user *) arg2,
(char __user *) arg3, (size_t) arg4,
- (void __user *) arg5);
+ (struct keyctl_kdf_params __user *) arg5);
default:
return -EOPNOTSUPP;
Regards,
--
Mat Martineau
Intel OTC
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