keys: Add capability-checking keyctl function

Add a keyctl function that requests a set of capability bits to find out
what features are supported.
Signed-off-by: David Howells <dhowells@redhat.com>

include/uapi/linux/keyctl.h

@@ -68,6 +68,7 @@
 #define KEYCTL_PKEY_VERIFY		28	/* Verify a public key signature */
 #define KEYCTL_RESTRICT_KEYRING		29	/* Restrict keys allowed to link to a keyring */
 #define KEYCTL_MOVE			30	/* Move keys between keyrings */
+#define KEYCTL_CAPABILITIES		31	/* Find capabilities of keyrings subsystem */
 
 /* keyctl structures */
 struct keyctl_dh_params {
@@ -115,4 +116,17 @@ struct keyctl_pkey_params {
 
 #define KEYCTL_MOVE_EXCL	0x00000001 /* Do not displace from the to-keyring */
 
+/*
+ * Capabilities flags.  The capabilities list is an array of 8-bit integers;
+ * each integer can carry up to 8 flags.
+ */
+#define KEYCTL_CAPS0_CAPABILITIES	0x01 /* KEYCTL_CAPABILITIES supported */
+#define KEYCTL_CAPS0_PERSISTENT_KEYRINGS 0x02 /* Persistent keyrings enabled */
+#define KEYCTL_CAPS0_DIFFIE_HELLMAN	0x04 /* Diffie-Hellman computation enabled */
+#define KEYCTL_CAPS0_PUBLIC_KEY		0x08 /* Public key ops enabled */
+#define KEYCTL_CAPS0_BIG_KEY		0x10 /* big_key-type enabled */
+#define KEYCTL_CAPS0_INVALIDATE		0x20 /* KEYCTL_INVALIDATE supported */
+#define KEYCTL_CAPS0_RESTRICT_KEYRING	0x40 /* KEYCTL_RESTRICT_KEYRING supported */
+#define KEYCTL_CAPS0_MOVE		0x80 /* KEYCTL_MOVE supported */
+
 #endif /*  _LINUX_KEYCTL_H */

security/keys/compat.c

@@ -162,6 +162,9 @@ COMPAT_SYSCALL_DEFINE5(keyctl, u32, option,
 	case KEYCTL_MOVE:
 		return keyctl_keyring_move(arg2, arg3, arg4, arg5);
 
+	case KEYCTL_CAPABILITIES:
+		return keyctl_capabilities(compat_ptr(arg2), arg3);
+
 	default:
 		return -EOPNOTSUPP;
 	}

security/keys/internal.h

@@ -329,6 +329,8 @@ static inline long keyctl_pkey_e_d_s(int op,
 }
 #endif
 
+extern long keyctl_capabilities(unsigned char __user *_buffer, size_t buflen);
+
 /*
  * Debugging key validation
  */

security/keys/keyctl.c

@@ -30,6 +30,18 @@
 
 #define KEY_MAX_DESC_SIZE 4096
 
+static const unsigned char keyrings_capabilities[1] = {
+	[0] = (KEYCTL_CAPS0_CAPABILITIES |
+	       (IS_ENABLED(CONFIG_PERSISTENT_KEYRINGS)	? KEYCTL_CAPS0_PERSISTENT_KEYRINGS : 0) |
+	       (IS_ENABLED(CONFIG_KEY_DH_OPERATIONS)	? KEYCTL_CAPS0_DIFFIE_HELLMAN : 0) |
+	       (IS_ENABLED(CONFIG_ASYMMETRIC_KEY_TYPE)	? KEYCTL_CAPS0_PUBLIC_KEY : 0) |
+	       (IS_ENABLED(CONFIG_BIG_KEYS)		? KEYCTL_CAPS0_BIG_KEY : 0) |
+	       KEYCTL_CAPS0_INVALIDATE |
+	       KEYCTL_CAPS0_RESTRICT_KEYRING |
+	       KEYCTL_CAPS0_MOVE
+	       ),
+};
+
 static int key_get_type_from_user(char *type,
 				  const char __user *_type,
 				  unsigned len)
@@ -1678,6 +1690,26 @@ long keyctl_restrict_keyring(key_serial_t id, const char __user *_type,
 	return ret;
 }
 
+/*
+ * Get keyrings subsystem capabilities.
+ */
+long keyctl_capabilities(unsigned char __user *_buffer, size_t buflen)
+{
+	size_t size = buflen;
+
+	if (size > 0) {
+		if (size > sizeof(keyrings_capabilities))
+			size = sizeof(keyrings_capabilities);
+		if (copy_to_user(_buffer, keyrings_capabilities, size) != 0)
+			return -EFAULT;
+		if (size < buflen &&
+		    clear_user(_buffer + size, buflen - size) != 0)
+			return -EFAULT;
+	}
+
+	return sizeof(keyrings_capabilities);
+}
+
 /*
  * The key control system call
  */
@@ -1824,6 +1856,9 @@ SYSCALL_DEFINE5(keyctl, int, option, unsigned long, arg2, unsigned long, arg3,
 					   (key_serial_t)arg4,
 					   (unsigned int)arg5);
 
+	case KEYCTL_CAPABILITIES:
+		return keyctl_capabilities((unsigned char __user *)arg2, (size_t)arg3);
+
 	default:
 		return -EOPNOTSUPP;
 	}