[PATCH net 9/9] rxrpc: Only call skb_cow_data() once per packet

[David Howells]

Move the call of skb_cow_data() from rxkad into rxrpc_recvmsg_data() and do
it as soon as the packet is first seen.  This means that we only call this
function once per packet, even for a jumbo packet with a bunch of
subpackets.

In rxkad, we then have to guess how large a scatter-gather table we need
for decryption, particularly in rxkad_verify_packet_2().  We do this either
by creating an sg table that should be large enough, or by looking at
nr_frags on the skb.

Fixes: 17926a79320a ("[AF_RXRPC]: Provide secure RxRPC sockets for use by userspace and kernel both")
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---

 net/rxrpc/ar-internal.h |    1 +
 net/rxrpc/input.c       |    1 +
 net/rxrpc/recvmsg.c     |   11 ++++++++++-
 net/rxrpc/rxkad.c       |   32 +++++++++-----------------------
 4 files changed, 21 insertions(+), 24 deletions(-)

diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index d784d58e0a0d..a42d6b833675 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -190,6 +190,7 @@ struct rxrpc_skb_priv {
 	u8		rx_flags;		/* Received packet flags */
 #define RXRPC_SKB_INCL_LAST	0x01		/* - Includes last packet */
 #define RXRPC_SKB_TX_BUFFER	0x02		/* - Is transmit buffer */
+#define RXRPC_SKB_NEEDS_COW	0x04		/* - Needs skb_cow_data() calling */
 	union {
 		int		remain;		/* amount of space remaining for next write */
 
diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index 660b7eed39b7..4df39f391e9d 100644
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c
@@ -448,6 +448,7 @@ static void rxrpc_input_data(struct rxrpc_call *call, struct sk_buff *skb)
 	}
 
 	atomic_set(&sp->nr_ring_pins, 1);
+	sp->rx_flags |= RXRPC_SKB_NEEDS_COW;
 
 	if (call->state == RXRPC_CALL_SERVER_RECV_REQUEST) {
 		unsigned long timo = READ_ONCE(call->next_req_timo);
diff --git a/net/rxrpc/recvmsg.c b/net/rxrpc/recvmsg.c
index 82bb48d96526..ef50580b5295 100644
--- a/net/rxrpc/recvmsg.c
+++ b/net/rxrpc/recvmsg.c
@@ -305,7 +305,7 @@ static int rxrpc_recvmsg_data(struct socket *sock, struct rxrpc_call *call,
 			      size_t len, int flags, size_t *_offset)
 {
 	struct rxrpc_skb_priv *sp;
-	struct sk_buff *skb;
+	struct sk_buff *skb, *trailer;
 	rxrpc_serial_t serial;
 	rxrpc_seq_t hard_ack, top, seq;
 	size_t remain;
@@ -343,6 +343,15 @@ static int rxrpc_recvmsg_data(struct socket *sock, struct rxrpc_call *call,
 		rxrpc_see_skb(skb, rxrpc_skb_seen);
 		sp = rxrpc_skb(skb);
 
+		if (sp->rx_flags & RXRPC_SKB_NEEDS_COW) {
+			ret2 = skb_cow_data(skb, 0, &trailer);
+			if (ret2 < 0) {
+				ret = ret2;
+				goto out;
+			}
+			sp->rx_flags &= ~RXRPC_SKB_NEEDS_COW;
+		}
+
 		if (!(flags & MSG_PEEK)) {
 			serial = sp->hdr.serial;
 			serial += call->rxtx_annotations[ix] & RXRPC_RX_ANNO_SUBPACKET;
diff --git a/net/rxrpc/rxkad.c b/net/rxrpc/rxkad.c
index ae8cd8926456..c60c520fde7c 100644
--- a/net/rxrpc/rxkad.c
+++ b/net/rxrpc/rxkad.c
@@ -187,10 +187,8 @@ static int rxkad_secure_packet_encrypt(const struct rxrpc_call *call,
 	struct rxrpc_skb_priv *sp;
 	struct rxrpc_crypt iv;
 	struct scatterlist sg[16];
-	struct sk_buff *trailer;
 	unsigned int len;
 	u16 check;
-	int nsg;
 	int err;
 
 	sp = rxrpc_skb(skb);
@@ -214,15 +212,14 @@ static int rxkad_secure_packet_encrypt(const struct rxrpc_call *call,
 	crypto_skcipher_encrypt(req);
 
 	/* we want to encrypt the skbuff in-place */
-	nsg = skb_cow_data(skb, 0, &trailer);
-	err = -ENOMEM;
-	if (nsg < 0 || nsg > 16)
+	err = -EMSGSIZE;
+	if (skb_shinfo(skb)->nr_frags > 16)
 		goto out;
 
 	len = data_size + call->conn->size_align - 1;
 	len &= ~(call->conn->size_align - 1);
 
-	sg_init_table(sg, nsg);
+	sg_init_table(sg, ARRAY_SIZE(sg));
 	err = skb_to_sgvec(skb, sg, 0, len);
 	if (unlikely(err < 0))
 		goto out;
@@ -319,11 +316,10 @@ static int rxkad_verify_packet_1(struct rxrpc_call *call, struct sk_buff *skb,
 	struct rxkad_level1_hdr sechdr;
 	struct rxrpc_crypt iv;
 	struct scatterlist sg[16];
-	struct sk_buff *trailer;
 	bool aborted;
 	u32 data_size, buf;
 	u16 check;
-	int nsg, ret;
+	int ret;
 
 	_enter("");
 
@@ -336,11 +332,7 @@ static int rxkad_verify_packet_1(struct rxrpc_call *call, struct sk_buff *skb,
 	/* Decrypt the skbuff in-place.  TODO: We really want to decrypt
 	 * directly into the target buffer.
 	 */
-	nsg = skb_cow_data(skb, 0, &trailer);
-	if (nsg < 0 || nsg > 16)
-		goto nomem;
-
-	sg_init_table(sg, nsg);
+	sg_init_table(sg, ARRAY_SIZE(sg));
 	ret = skb_to_sgvec(skb, sg, offset, 8);
 	if (unlikely(ret < 0))
 		return ret;
@@ -388,10 +380,6 @@ static int rxkad_verify_packet_1(struct rxrpc_call *call, struct sk_buff *skb,
 	if (aborted)
 		rxrpc_send_abort_packet(call);
 	return -EPROTO;
-
-nomem:
-	_leave(" = -ENOMEM");
-	return -ENOMEM;
 }
 
 /*
@@ -406,7 +394,6 @@ static int rxkad_verify_packet_2(struct rxrpc_call *call, struct sk_buff *skb,
 	struct rxkad_level2_hdr sechdr;
 	struct rxrpc_crypt iv;
 	struct scatterlist _sg[4], *sg;
-	struct sk_buff *trailer;
 	bool aborted;
 	u32 data_size, buf;
 	u16 check;
@@ -423,12 +410,11 @@ static int rxkad_verify_packet_2(struct rxrpc_call *call, struct sk_buff *skb,
 	/* Decrypt the skbuff in-place.  TODO: We really want to decrypt
 	 * directly into the target buffer.
 	 */
-	nsg = skb_cow_data(skb, 0, &trailer);
-	if (nsg < 0)
-		goto nomem;
-
 	sg = _sg;
-	if (unlikely(nsg > 4)) {
+	nsg = skb_shinfo(skb)->nr_frags;
+	if (nsg <= 4) {
+		nsg = 4;
+	} else {
 		sg = kmalloc_array(nsg, sizeof(*sg), GFP_NOIO);
 		if (!sg)
 			goto nomem;