rxrpc: Provide a cmsg to specify the amount of Tx data for a call

Provide a control message that can be specified on the first sendmsg() of a
client call or the first sendmsg() of a service response to indicate the
total length of the data to be transmitted for that call.

Currently, because the length of the payload of an encrypted DATA packet is
encrypted in front of the data, the packet cannot be encrypted until we
know how much data it will hold.

By specifying the length at the beginning of the transmit phase, each DATA
packet length can be set before we start loading data from userspace (where
several sendmsg() calls may contribute to a particular packet).

An error will be returned if too little or too much data is presented in
the Tx phase.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 17 insertions, 1 deletions

diff --git a/fs/afs/rxrpc.c b/fs/afs/rxrpc.c
index d5990eb160bd..02781e78ffb6 100644
--- a/fs/afs/rxrpc.c
+++ b/fs/afs/rxrpc.c
@@ -341,6 +341,7 @@ int afs_make_call(struct in_addr *addr, struct afs_call *call, gfp_t gfp,
 	struct msghdr msg;
 	struct kvec iov[1];
 	size_t offset;
+	s64 tx_total_len;
 	u32 abort_code;
 	int ret;
 
@@ -364,9 +365,20 @@ int afs_make_call(struct in_addr *addr, struct afs_call *call, gfp_t gfp,
 	srx.transport.sin.sin_port = call->port;
 	memcpy(&srx.transport.sin.sin_addr, addr, 4);
 
+	/* Work out the length we're going to transmit.  This is awkward for
+	 * calls such as FS.StoreData where there's an extra injection of data
+	 * after the initial fixed part.
+	 */
+	tx_total_len = call->request_size;
+	if (call->send_pages) {
+		tx_total_len += call->last_to - call->first_offset;
+		tx_total_len += (call->last - call->first) * PAGE_SIZE;
+	}
+
 	/* create a call */
 	rxcall = rxrpc_kernel_begin_call(afs_socket, &srx, call->key,
-					 (unsigned long) call, gfp,
+					 (unsigned long)call,
+					 tx_total_len, gfp,
 					 (async ?
 					  afs_wake_up_async_call :
 					  afs_wake_up_call_waiter));
@@ -738,6 +750,8 @@ void afs_send_empty_reply(struct afs_call *call)
 
 	_enter("");
 
+	rxrpc_kernel_set_tx_length(afs_socket, call->rxcall, 0);
+
 	msg.msg_name		= NULL;
 	msg.msg_namelen		= 0;
 	iov_iter_kvec(&msg.msg_iter, WRITE | ITER_KVEC, NULL, 0, 0);
@@ -772,6 +786,8 @@ void afs_send_simple_reply(struct afs_call *call, const void *buf, size_t len)
 
 	_enter("");
 
+	rxrpc_kernel_set_tx_length(afs_socket, call->rxcall, len);
+
 	iov[0].iov_base		= (void *) buf;
 	iov[0].iov_len		= len;
 	msg.msg_name		= NULL;