KEYS: Add placeholder for KDF usage with DH

The values computed during Diffie-Hellman key exchange are often used in combination with key derivation functions to create cryptographic keys. Add a placeholder for a later implementation to configure a key derivation function that will transform the Diffie-Hellman result returned by the KEYCTL_DH_COMPUTE command. [This patch was stripped down from a patch produced by Mat Martineau that had a bug in the compat code - so for the moment Stephan's patch simply requires that the placeholder argument must be NULL] Original-signed-off-by: Mat Martineau <[email protected]> Signed-off-by: Stephan Mueller <[email protected]> Signed-off-by: David Howells <[email protected]> Signed-off-by: James Morris <[email protected]>
mrcsosa · Jun 3, 2016 · 4693fc7 · 4693fc7
1 parent 4340fa5
commit 4693fc7
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Showing 5 changed files with 17 additions and 7 deletions.
diff --git a/Documentation/security/keys.txt b/Documentation/security/keys.txt
@@ -826,7 +826,8 @@ The keyctl syscall functions are:
  (*) Compute a Diffie-Hellman shared secret or public key
 
        long keyctl(KEYCTL_DH_COMPUTE, struct keyctl_dh_params *params,
-		   char *buffer, size_t buflen);
+		   char *buffer, size_t buflen,
+		   void *reserved);
 
      The params struct contains serial numbers for three keys:
 
@@ -843,6 +844,8 @@ The keyctl syscall functions are:
      public key.  If the base is the remote public key, the result is
      the shared secret.
 
+     The reserved argument must be set to NULL.
+
      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

diff --git a/security/keys/compat.c b/security/keys/compat.c
@@ -134,7 +134,7 @@ COMPAT_SYSCALL_DEFINE5(keyctl, u32, option,
 
 	case KEYCTL_DH_COMPUTE:
 		return keyctl_dh_compute(compat_ptr(arg2), compat_ptr(arg3),
-					 arg4);
+					 arg4, compat_ptr(arg5));
 
 	default:
 		return -EOPNOTSUPP;

diff --git a/security/keys/dh.c b/security/keys/dh.c
@@ -78,7 +78,8 @@ static ssize_t mpi_from_key(key_serial_t keyid, size_t maxlen, MPI *mpi)
 }
 
 long keyctl_dh_compute(struct keyctl_dh_params __user *params,
-		       char __user *buffer, size_t buflen)
+		       char __user *buffer, size_t buflen,
+		       void __user *reserved)
 {
 	long ret;
 	MPI base, private, prime, result;
@@ -97,6 +98,11 @@ long keyctl_dh_compute(struct keyctl_dh_params __user *params,
 		goto out;
 	}
 
+	if (reserved) {
+		ret = -EINVAL;
+		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,

diff --git a/security/keys/internal.h b/security/keys/internal.h
@@ -260,10 +260,11 @@ static inline long keyctl_get_persistent(uid_t uid, key_serial_t destring)
 
 #ifdef CONFIG_KEY_DH_OPERATIONS
 extern long keyctl_dh_compute(struct keyctl_dh_params __user *, char __user *,
-			      size_t);
+			      size_t, void __user *);
 #else
 static inline long keyctl_dh_compute(struct keyctl_dh_params __user *params,
-				     char __user *buffer, size_t buflen)
+				     char __user *buffer, size_t buflen,
+				     void __user *reserved)
 {
 	return -EOPNOTSUPP;
 }

diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
@@ -1688,8 +1688,8 @@ 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);
+					 (char __user *) arg3, (size_t) arg4,
+					 (void __user *) arg5);
 
 	default:
 		return -EOPNOTSUPP;