RxRPC: Allow RxRPC keys to be read

Allow RxRPC keys to be read.  This is to allow pioctl() to be implemented in
userspace.  RxRPC keys are read out in XDR format.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/rxrpc/ar-key.c

@@ -29,6 +29,7 @@ static int rxrpc_instantiate_s(struct key *, const void *, size_t);
 static void rxrpc_destroy(struct key *);
 static void rxrpc_destroy_s(struct key *);
 static void rxrpc_describe(const struct key *, struct seq_file *);
+static long rxrpc_read(const struct key *, char __user *, size_t);
 
 /*
  * rxrpc defined keys take an arbitrary string as the description and an
@@ -40,6 +41,7 @@ struct key_type key_type_rxrpc = {
 	.match		= user_match,
 	.destroy	= rxrpc_destroy,
 	.describe	= rxrpc_describe,
+	.read		= rxrpc_read,
 };
 EXPORT_SYMBOL(key_type_rxrpc);
 
@@ -592,3 +594,110 @@ struct key *rxrpc_get_null_key(const char *keyname)
 	return key;
 }
 EXPORT_SYMBOL(rxrpc_get_null_key);
+
+/*
+ * read the contents of an rxrpc key
+ * - this returns the result in XDR form
+ */
+static long rxrpc_read(const struct key *key,
+		       char __user *buffer, size_t buflen)
+{
+	struct rxrpc_key_token *token;
+	size_t size, toksize;
+	__be32 __user *xdr;
+	u32 cnlen, tktlen, ntoks, zero;
+
+	_enter("");
+
+	/* we don't know what form we should return non-AFS keys in */
+	if (memcmp(key->description, "afs@", 4) != 0)
+		return -EOPNOTSUPP;
+	cnlen = strlen(key->description + 4);
+
+	/* AFS keys we return in XDR form, so we need to work out the size of
+	 * the XDR */
+	size = 2 * 4;	/* flags, cellname len */
+	size += (cnlen + 3) & ~3;	/* cellname */
+	size += 1 * 4;	/* token count */
+
+	ntoks = 0;
+	for (token = key->payload.data; token; token = token->next) {
+		switch (token->security_index) {
+		case RXRPC_SECURITY_RXKAD:
+			size += 2 * 4;	/* length, security index (switch ID) */
+			size += 8 * 4;	/* viceid, kvno, key*2, begin, end,
+					 * primary, tktlen */
+			size += (token->kad->ticket_len + 3) & ~3; /* ticket */
+			ntoks++;
+			break;
+
+		default: /* can't encode */
+			break;
+		}
+	}
+
+	if (!buffer || buflen < size)
+		return size;
+
+	xdr = (__be32 __user *) buffer;
+	zero = 0;
+#define ENCODE(x)				\
+	do {					\
+		__be32 y = htonl(x);		\
+		if (put_user(y, xdr++) < 0)	\
+			goto fault;		\
+	} while(0)
+
+	ENCODE(0);	/* flags */
+	ENCODE(cnlen);	/* cellname length */
+	if (copy_to_user(xdr, key->description + 4, cnlen) != 0)
+		goto fault;
+	if (cnlen & 3 &&
+	    copy_to_user((u8 *)xdr + cnlen, &zero, 4 - (cnlen & 3)) != 0)
+		goto fault;
+	xdr += (cnlen + 3) >> 2;
+	ENCODE(ntoks);	/* token count */
+
+	for (token = key->payload.data; token; token = token->next) {
+		toksize = 1 * 4;	/* sec index */
+
+		switch (token->security_index) {
+		case RXRPC_SECURITY_RXKAD:
+			toksize += 8 * 4;
+			toksize += (token->kad->ticket_len + 3) & ~3;
+			ENCODE(toksize);
+			ENCODE(token->security_index);
+			ENCODE(token->kad->vice_id);
+			ENCODE(token->kad->kvno);
+			if (copy_to_user(xdr, token->kad->session_key, 8) != 0)
+				goto fault;
+			xdr += 8 >> 2;
+			ENCODE(token->kad->start);
+			ENCODE(token->kad->expiry);
+			ENCODE(token->kad->primary_flag);
+			tktlen = token->kad->ticket_len;
+			ENCODE(tktlen);
+			if (copy_to_user(xdr, token->kad->ticket, tktlen) != 0)
+				goto fault;
+			if (tktlen & 3 &&
+			    copy_to_user((u8 *)xdr + tktlen, &zero,
+					 4 - (tktlen & 3)) != 0)
+				goto fault;
+			xdr += (tktlen + 3) >> 2;
+			break;
+
+		default:
+			break;
+		}
+	}
+
+#undef ENCODE
+
+	ASSERTCMP((char __user *) xdr - buffer, ==, size);
+	_leave(" = %zu", size);
+	return size;
+
+fault:
+	_leave(" = -EFAULT");
+	return -EFAULT;
+}