net: change sock_queue_rcv_skb_reason() to return a drop_reason

Change sock_queue_rcv_skb_reason() to return the drop_reason directly
instead of using a reference.

This is part of an effort to remove stack canaries and reduce bloat.

$ scripts/bloat-o-meter -t vmlinux.old vmlinux.new
add/remove: 0/0 grow/shrink: 3/7 up/down: 79/-301 (-222)
Function                                     old     new   delta
vsock_queue_rcv_skb                           50      79     +29
ipmr_cache_report                           1290    1315     +25
ip6mr_cache_report                          1322    1347     +25
packet_rcv_spkt                              329     327      -2
sock_queue_rcv_skb_reason                    166     128     -38
raw_rcv_skb                                  122      80     -42
ping_queue_rcv_skb                           109      61     -48
ping_rcv                                     215     162     -53
rawv6_rcv_skb                                278     224     -54
raw_rcv                                      591     527     -64
Total: Before=29722890, After=29722668, chg -0.00%

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260409145625.2306224-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/sock.h

@@ -2502,12 +2502,23 @@ int __sk_queue_drop_skb(struct sock *sk, struct sk_buff_head *sk_queue,
 					   struct sk_buff *skb));
 int __sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
 
-int sock_queue_rcv_skb_reason(struct sock *sk, struct sk_buff *skb,
-			      enum skb_drop_reason *reason);
+enum skb_drop_reason
+sock_queue_rcv_skb_reason(struct sock *sk, struct sk_buff *skb);
 
 static inline int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 {
-	return sock_queue_rcv_skb_reason(sk, skb, NULL);
+	enum skb_drop_reason drop_reason = sock_queue_rcv_skb_reason(sk, skb);
+
+	switch (drop_reason) {
+	case SKB_DROP_REASON_SOCKET_RCVBUFF:
+		return -ENOMEM;
+	case SKB_DROP_REASON_PROTO_MEM:
+		return -ENOBUFS;
+	case 0:
+		return 0;
+	default:
+		return -EPERM;
+	}
 }
 
 int sock_queue_err_skb(struct sock *sk, struct sk_buff *skb);

net/can/bcm.c

@@ -363,7 +363,6 @@ static void bcm_send_to_user(struct bcm_op *op, struct bcm_msg_head *head,
 	struct sockaddr_can *addr;
 	struct sock *sk = op->sk;
 	unsigned int datalen = head->nframes * op->cfsiz;
-	int err;
 	unsigned int *pflags;
 	enum skb_drop_reason reason;
 
@@ -420,8 +419,8 @@ static void bcm_send_to_user(struct bcm_op *op, struct bcm_msg_head *head,
 	addr->can_family  = AF_CAN;
 	addr->can_ifindex = op->rx_ifindex;
 
-	err = sock_queue_rcv_skb_reason(sk, skb, &reason);
-	if (err < 0) {
+	reason = sock_queue_rcv_skb_reason(sk, skb);
+	if (reason) {
 		struct bcm_sock *bo = bcm_sk(sk);
 
 		sk_skb_reason_drop(sk, skb, reason);

net/can/isotp.c

@@ -291,7 +291,8 @@ static void isotp_rcv_skb(struct sk_buff *skb, struct sock *sk)
 	addr->can_family = AF_CAN;
 	addr->can_ifindex = skb->dev->ifindex;
 
-	if (sock_queue_rcv_skb_reason(sk, skb, &reason) < 0)
+	reason = sock_queue_rcv_skb_reason(sk, skb);
+	if (reason)
 		sk_skb_reason_drop(sk, skb, reason);
 }
 

net/can/j1939/socket.c

@@ -333,7 +333,8 @@ static void j1939_sk_recv_one(struct j1939_sock *jsk, struct sk_buff *oskb)
 	if (skb->sk)
 		skcb->msg_flags |= MSG_DONTROUTE;
 
-	if (sock_queue_rcv_skb_reason(&jsk->sk, skb, &reason) < 0)
+	reason = sock_queue_rcv_skb_reason(&jsk->sk, skb);
+	if (reason)
 		sk_skb_reason_drop(&jsk->sk, skb, reason);
 }
 

net/can/raw.c

@@ -207,7 +207,8 @@ static void raw_rcv(struct sk_buff *oskb, void *data)
 	if (oskb->sk == sk)
 		*pflags |= MSG_CONFIRM;
 
-	if (sock_queue_rcv_skb_reason(sk, skb, &reason) < 0)
+	reason = sock_queue_rcv_skb_reason(sk, skb);
+	if (reason)
 		sk_skb_reason_drop(sk, skb, reason);
 }
 

net/core/sock.c

@@ -520,32 +520,24 @@ int __sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 }
 EXPORT_SYMBOL(__sock_queue_rcv_skb);
 
-int sock_queue_rcv_skb_reason(struct sock *sk, struct sk_buff *skb,
-			      enum skb_drop_reason *reason)
+enum skb_drop_reason
+sock_queue_rcv_skb_reason(struct sock *sk, struct sk_buff *skb)
 {
 	enum skb_drop_reason drop_reason;
 	int err;
 
 	err = sk_filter_reason(sk, skb, &drop_reason);
 	if (err)
-		goto out;
+		return drop_reason;
 
 	err = __sock_queue_rcv_skb(sk, skb);
 	switch (err) {
 	case -ENOMEM:
-		drop_reason = SKB_DROP_REASON_SOCKET_RCVBUFF;
-		break;
+		return SKB_DROP_REASON_SOCKET_RCVBUFF;
 	case -ENOBUFS:
-		drop_reason = SKB_DROP_REASON_PROTO_MEM;
-		break;
-	default:
-		drop_reason = SKB_NOT_DROPPED_YET;
-		break;
+		return SKB_DROP_REASON_PROTO_MEM;
 	}
-out:
-	if (reason)
-		*reason = drop_reason;
-	return err;
+	return SKB_NOT_DROPPED_YET;
 }
 EXPORT_SYMBOL(sock_queue_rcv_skb_reason);
 

net/ipv4/ping.c

@@ -935,7 +935,8 @@ static enum skb_drop_reason __ping_queue_rcv_skb(struct sock *sk,
 
 	pr_debug("ping_queue_rcv_skb(sk=%p,sk->num=%d,skb=%p)\n",
 		 inet_sk(sk), inet_sk(sk)->inet_num, skb);
-	if (sock_queue_rcv_skb_reason(sk, skb, &reason) < 0) {
+	reason = sock_queue_rcv_skb_reason(sk, skb);
+	if (reason) {
 		sk_skb_reason_drop(sk, skb, reason);
 		pr_debug("ping_queue_rcv_skb -> failed\n");
 		return reason;

net/ipv4/raw.c

@@ -300,7 +300,8 @@ static int raw_rcv_skb(struct sock *sk, struct sk_buff *skb)
 	/* Charge it to the socket. */
 
 	ipv4_pktinfo_prepare(sk, skb, true);
-	if (sock_queue_rcv_skb_reason(sk, skb, &reason) < 0) {
+	reason = sock_queue_rcv_skb_reason(sk, skb);
+	if (reason) {
 		sk_skb_reason_drop(sk, skb, reason);
 		return NET_RX_DROP;
 	}

net/ipv6/raw.c

@@ -369,7 +369,8 @@ static inline int rawv6_rcv_skb(struct sock *sk, struct sk_buff *skb)
 
 	/* Charge it to the socket. */
 	skb_dst_drop(skb);
-	if (sock_queue_rcv_skb_reason(sk, skb, &reason) < 0) {
+	reason = sock_queue_rcv_skb_reason(sk, skb);
+	if (reason) {
 		sk_skb_reason_drop(sk, skb, reason);
 		return NET_RX_DROP;
 	}