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Commit ddbb4114 authored by Mat Martineau's avatar Mat Martineau Committed by David Howells
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KEYS: Add KEYCTL_DH_COMPUTE command 



This adds userspace access to Diffie-Hellman computations through a
new keyctl() syscall command to calculate shared secrets or public
keys using input parameters stored in the keyring.

Input key ids are provided in a struct due to the current 5-arg limit
for the keyctl syscall. Only user keys are supported in order to avoid
exposing the content of logon or encrypted keys.

The output is written to the provided buffer, based on the assumption
that the values are only needed in userspace.

Future support for other types of key derivation would involve a new
command, like KEYCTL_ECDH_COMPUTE.

Once Diffie-Hellman support is included in the crypto API, this code
can be converted to use the crypto API to take advantage of possible
hardware acceleration and reduce redundant code.

Signed-off-by: default avatarMat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
parent 13100a72

Documentation/security/keys.txt

+30 −0
Original line number Diff line number Diff line
@@ -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

include/uapi/linux/keyctl.h

+10 −0
Original line number Diff line number Diff line
@@ -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 */

security/keys/Kconfig

+11 −0
Original line number Diff line number Diff line
@@ -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.

security/keys/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -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

security/keys/compat.c

+4 −0
Original line number Diff line number Diff line
@@ -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;

	}