8 files changed, 233 insertions, 0 deletions

diff --git a/Documentation/security/keys.txt b/Documentation/security/keys.txt
index 8c183873b2b7..a2f70cf6763a 100644
--- a/Documentation/security/keys.txt
+++ b/Documentation/security/keys.txt
@@ -823,6 +823,36 @@ The keyctl syscall functions are:
      A process must have search permission on the key for this function to be
      successful.
 
+ (*) Compute a Diffie-Hellman shared secret or public key
+
+       long keyctl(KEYCTL_DH_COMPUTE, struct keyctl_dh_params *params,
+                   char *buffer, size_t buflen);
+
+     The params struct contains serial numbers for three keys:
+
+         - The prime, p, known to both parties
+         - The local private key
+         - The base integer, which is either a shared generator or the
+           remote public key
+
+     The value computed is:
+
+        result = base ^ private (mod prime)
+
+     If the base is the shared generator, the result is the local
+     public key.  If the base is the remote public key, the result is
+     the shared secret.
+
+     The buffer length must be at least the length of the prime, or zero.
+
+     If the buffer length is nonzero, the length of the result is
+     returned when it is successfully calculated and copied in to the
+     buffer. When the buffer length is zero, the minimum required
+     buffer length is returned.
+
+     This function will return error EOPNOTSUPP if the key type is not
+     supported, error ENOKEY if the key could not be found, or error
+     EACCES if the key is not readable by the caller.
 
 ===============
 KERNEL SERVICES
diff --git a/include/uapi/linux/keyctl.h b/include/uapi/linux/keyctl.h
index 840cb990abe2..86eddd6241f3 100644
--- a/include/uapi/linux/keyctl.h
+++ b/include/uapi/linux/keyctl.h
@@ -12,6 +12,8 @@
 #ifndef _LINUX_KEYCTL_H
 #define _LINUX_KEYCTL_H
 
+#include <linux/types.h>
+
 /* special process keyring shortcut IDs */
 #define KEY_SPEC_THREAD_KEYRING         -1      /* - key ID for thread-specific keyring */
 #define KEY_SPEC_PROCESS_KEYRING        -2      /* - key ID for process-specific keyring */
@@ -57,5 +59,13 @@
 #define KEYCTL_INSTANTIATE_IOV          20      /* instantiate a partially constructed key */
 #define KEYCTL_INVALIDATE               21      /* invalidate a key */
 #define KEYCTL_GET_PERSISTENT           22      /* get a user's persistent keyring */
+#define KEYCTL_DH_COMPUTE               23      /* Compute Diffie-Hellman values */
+
+/* keyctl structures */
+struct keyctl_dh_params {
+        __s32 private;
+        __s32 prime;
+        __s32 base;
+};
 
 #endif /*  _LINUX_KEYCTL_H */
diff --git a/security/keys/Kconfig b/security/keys/Kconfig
index 45828095080d..f826e8739023 100644
--- a/security/keys/Kconfig
+++ b/security/keys/Kconfig
@@ -85,3 +85,14 @@ config ENCRYPTED_KEYS
           Userspace only ever sees/stores encrypted blobs.
 
           If you are unsure as to whether this is required, answer N.
+
+config KEY_DH_OPERATIONS
+       bool "Diffie-Hellman operations on retained keys"
+       depends on KEYS
+       select MPILIB
+       help
+         This option provides support for calculating Diffie-Hellman
+         public keys and shared secrets using values stored as keys
+         in the kernel.
+
+         If you are unsure as to whether this is required, answer N.
diff --git a/security/keys/Makefile b/security/keys/Makefile
index dfb3a7bededf..1fd4a16e6daf 100644
--- a/security/keys/Makefile
+++ b/security/keys/Makefile
@@ -19,6 +19,7 @@ obj-$(CONFIG_KEYS_COMPAT) += compat.o
 obj-$(CONFIG_PROC_FS) += proc.o
 obj-$(CONFIG_SYSCTL) += sysctl.o
 obj-$(CONFIG_PERSISTENT_KEYRINGS) += persistent.o
+obj-$(CONFIG_KEY_DH_OPERATIONS) += dh.o
 
 #
 # Key types
diff --git a/security/keys/compat.c b/security/keys/compat.c
index 25430a3aa7f7..c8783b3b628c 100644
--- a/security/keys/compat.c
+++ b/security/keys/compat.c
@@ -132,6 +132,10 @@ COMPAT_SYSCALL_DEFINE5(keyctl, u32, option,
         case KEYCTL_GET_PERSISTENT:
                 return keyctl_get_persistent(arg2, arg3);
 
+        case KEYCTL_DH_COMPUTE:
+                return keyctl_dh_compute(compat_ptr(arg2), compat_ptr(arg3),
+                                         arg4);
+
         default:
                 return -EOPNOTSUPP;
         }
diff --git a/security/keys/dh.c b/security/keys/dh.c
new file mode 100644
index 000000000000..880505a4b9f1
--- /dev/null
+++ b/security/keys/dh.c
@@ -0,0 +1,160 @@
+/* Crypto operations using stored keys
+ *
+ * Copyright (c) 2016, Intel Corporation
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/mpi.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <keys/user-type.h>
+#include "internal.h"
+
+/*
+ * Public key or shared secret generation function [RFC2631 sec 2.1.1]
+ *
+ * ya = g^xa mod p;
+ * or
+ * ZZ = yb^xa mod p;
+ *
+ * where xa is the local private key, ya is the local public key, g is
+ * the generator, p is the prime, yb is the remote public key, and ZZ
+ * is the shared secret.
+ *
+ * Both are the same calculation, so g or yb are the "base" and ya or
+ * ZZ are the "result".
+ */
+static int do_dh(MPI result, MPI base, MPI xa, MPI p)
+{
+        return mpi_powm(result, base, xa, p);
+}
+
+static ssize_t mpi_from_key(key_serial_t keyid, size_t maxlen, MPI *mpi)
+{
+        struct key *key;
+        key_ref_t key_ref;
+        long status;
+        ssize_t ret;
+
+        key_ref = lookup_user_key(keyid, 0, KEY_NEED_READ);
+        if (IS_ERR(key_ref)) {
+                ret = -ENOKEY;
+                goto error;
+        }
+
+        key = key_ref_to_ptr(key_ref);
+
+        ret = -EOPNOTSUPP;
+        if (key->type == &key_type_user) {
+                down_read(&key->sem);
+                status = key_validate(key);
+                if (status == 0) {
+                        const struct user_key_payload *payload;
+
+                        payload = user_key_payload(key);
+
+                        if (maxlen == 0) {
+                                *mpi = NULL;
+                                ret = payload->datalen;
+                        } else if (payload->datalen <= maxlen) {
+                                *mpi = mpi_read_raw_data(payload->data,
+                                                         payload->datalen);
+                                if (*mpi)
+                                        ret = payload->datalen;
+                        } else {
+                                ret = -EINVAL;
+                        }
+                }
+                up_read(&key->sem);
+        }
+
+        key_put(key);
+error:
+        return ret;
+}
+
+long keyctl_dh_compute(struct keyctl_dh_params __user *params,
+                       char __user *buffer, size_t buflen)
+{
+        long ret;
+        MPI base, private, prime, result;
+        unsigned nbytes;
+        struct keyctl_dh_params pcopy;
+        uint8_t *kbuf;
+        ssize_t keylen;
+        size_t resultlen;
+
+        if (!params || (!buffer && buflen)) {
+                ret = -EINVAL;
+                goto out;
+        }
+        if (copy_from_user(&pcopy, params, sizeof(pcopy)) != 0) {
+                ret = -EFAULT;
+                goto out;
+        }
+
+        keylen = mpi_from_key(pcopy.prime, buflen, &prime);
+        if (keylen < 0 || !prime) {
+                /* buflen == 0 may be used to query the required buffer size,
+                 * which is the prime key length.
+                 */
+                ret = keylen;
+                goto out;
+        }
+
+        /* The result is never longer than the prime */
+        resultlen = keylen;
+
+        keylen = mpi_from_key(pcopy.base, SIZE_MAX, &base);
+        if (keylen < 0 || !base) {
+                ret = keylen;
+                goto error1;
+        }
+
+        keylen = mpi_from_key(pcopy.private, SIZE_MAX, &private);
+        if (keylen < 0 || !private) {
+                ret = keylen;
+                goto error2;
+        }
+
+        result = mpi_alloc(0);
+        if (!result) {
+                ret = -ENOMEM;
+                goto error3;
+        }
+
+        kbuf = kmalloc(resultlen, GFP_KERNEL);
+        if (!kbuf) {
+                ret = -ENOMEM;
+                goto error4;
+        }
+
+        ret = do_dh(result, base, private, prime);
+        if (ret)
+                goto error5;
+
+        ret = mpi_read_buffer(result, kbuf, resultlen, &nbytes, NULL);
+        if (ret != 0)
+                goto error5;
+
+        ret = nbytes;
+        if (copy_to_user(buffer, kbuf, nbytes) != 0)
+                ret = -EFAULT;
+
+error5:
+        kfree(kbuf);
+error4:
+        mpi_free(result);
+error3:
+        mpi_free(private);
+error2:
+        mpi_free(base);
+error1:
+        mpi_free(prime);
+out:
+        return ret;
+}
diff --git a/security/keys/internal.h b/security/keys/internal.h
index 5105c2c2da75..8ec7a528365d 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -15,6 +15,7 @@
 #include <linux/sched.h>
 #include <linux/key-type.h>
 #include <linux/task_work.h>
+#include <linux/keyctl.h>
 
 struct iovec;
 
@@ -257,6 +258,17 @@ static inline long keyctl_get_persistent(uid_t uid, key_serial_t destring)
 }
 #endif
 
+#ifdef CONFIG_KEY_DH_OPERATIONS
+extern long keyctl_dh_compute(struct keyctl_dh_params __user *, char __user *,
+                              size_t);
+#else
+static inline long keyctl_dh_compute(struct keyctl_dh_params __user *params,
+                                     char __user *buffer, size_t buflen)
+{
+        return -EOPNOTSUPP;
+}
+#endif
+
 /*
  * Debugging key validation
  */
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index ed73c6c1c326..3b135a0af344 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1686,6 +1686,11 @@ SYSCALL_DEFINE5(keyctl, int, option, unsigned long, arg2, unsigned long, arg3,
         case KEYCTL_GET_PERSISTENT:
                 return keyctl_get_persistent((uid_t)arg2, (key_serial_t)arg3);
 
+        case KEYCTL_DH_COMPUTE:
+                return keyctl_dh_compute((struct keyctl_dh_params __user *) arg2,
+                                         (char __user *) arg3,
+                                         (size_t) arg4);
+
         default:
                 return -EOPNOTSUPP;
         }