[PATCH net-next 12/23] rxrpc: Allow for a security trailer in a packet

[David Howells <dhowells@redhat.com>]

Allow for a security trailer to added to a packet.  The size is stored in
conn->security_trailer.  Note any size alignment set by the security class
must be applied after subtracting the trailer (but the alignment includes
the security header, which is assumed to be encrypted).

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

 net/rxrpc/ar-internal.h |    1 +
 net/rxrpc/sendmsg.c     |   28 ++++++++++++++++------------
 2 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index dce48162f6c2..5aacd6d7cf28 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -455,6 +455,7 @@ struct rxrpc_connection {
 	u32			service_id;	/* Service ID, possibly upgraded */
 	u8			size_align;	/* data size alignment (for security) */
 	u8			security_size;	/* security header size */
+	u8			security_trailer; /* Security trailer size */
 	u8			security_ix;	/* security type */
 	u8			out_clientflag;	/* RXRPC_CLIENT_INITIATED if we are client */
 	u8			bundle_shift;	/* Index into bundle->avail_chans */
diff --git a/net/rxrpc/sendmsg.c b/net/rxrpc/sendmsg.c
index d27140c836cc..258224bb1227 100644
--- a/net/rxrpc/sendmsg.c
+++ b/net/rxrpc/sendmsg.c
@@ -327,7 +327,7 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
 			rxrpc_send_ack_packet(call, false, NULL);
 
 		if (!skb) {
-			size_t size, chunk, max, space;
+			size_t size, chunk, limit, space, shdr;
 
 			_debug("alloc");
 
@@ -342,18 +342,22 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
 					goto maybe_error;
 			}
 
-			max = RXRPC_JUMBO_DATALEN;
-			max -= call->conn->security_size;
-			max &= ~(call->conn->size_align - 1UL);
-
-			chunk = max;
-			if (chunk > msg_data_left(msg) && !more)
+			/* Work out the maximum size of a packet.  Assume that
+			 * the security header is going to be in the padded
+			 * region (enc blocksize), but the trailer is not.
+			 */
+			shdr = call->conn->security_size;
+			limit = RXRPC_JUMBO_DATALEN;
+			limit -= call->conn->security_trailer;
+			space = round_down(limit, call->conn->size_align);
+
+			chunk = space - shdr;
+			if (msg_data_left(msg) < chunk && !more) {
 				chunk = msg_data_left(msg);
+				space = round_up(shdr + chunk, call->conn->size_align);
+			}
 
-			space = chunk + call->conn->size_align;
-			space &= ~(call->conn->size_align - 1UL);
-
-			size = space + call->conn->security_size;
+			size = space + call->conn->security_trailer;
 
 			_debug("SIZE: %zu/%zu/%zu", chunk, space, size);
 
@@ -425,7 +429,7 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
 			size_t pad;
 
 			/* pad out if we're using security */
-			if (conn->security_ix) {
+			if (conn->size_align > 0) {
 				pad = conn->security_size + skb->mark;
 				pad = conn->size_align - pad;
 				pad &= conn->size_align - 1;