Merge branch 'net-skb_put_padto-fixes'

Eric Dumazet says:

====================
net: skb_put_padto() fixes

sysbot reported a bug in qrtr leading to use-after-free.

First patch fixes the issue.

Second patch addes __must_check attribute to avoid similar
issues in the future.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -3223,8 +3223,9 @@ static inline int skb_padto(struct sk_buff *skb, unsigned int len)
  *	is untouched. Otherwise it is extended. Returns zero on
  *	success. The skb is freed on error if @free_on_error is true.
  */
-static inline int __skb_put_padto(struct sk_buff *skb, unsigned int len,
-				  bool free_on_error)
+static inline int __must_check __skb_put_padto(struct sk_buff *skb,
+					       unsigned int len,
+					       bool free_on_error)
 {
 	unsigned int size = skb->len;
 
@@ -3247,7 +3248,7 @@ static inline int __skb_put_padto(struct sk_buff *skb, unsigned int len,
  *	is untouched. Otherwise it is extended. Returns zero on
  *	success. The skb is freed on error.
  */
-static inline int skb_put_padto(struct sk_buff *skb, unsigned int len)
+static inline int __must_check skb_put_padto(struct sk_buff *skb, unsigned int len)
 {
 	return __skb_put_padto(skb, len, true);
 }

net/qrtr/qrtr.c

@@ -332,8 +332,7 @@ static int qrtr_node_enqueue(struct qrtr_node *node, struct sk_buff *skb,
 {
 	struct qrtr_hdr_v1 *hdr;
 	size_t len = skb->len;
-	int rc = -ENODEV;
-	int confirm_rx;
+	int rc, confirm_rx;
 
 	confirm_rx = qrtr_tx_wait(node, to->sq_node, to->sq_port, type);
 	if (confirm_rx < 0) {
@@ -357,15 +356,17 @@ static int qrtr_node_enqueue(struct qrtr_node *node, struct sk_buff *skb,
 	hdr->size = cpu_to_le32(len);
 	hdr->confirm_rx = !!confirm_rx;
 
-	skb_put_padto(skb, ALIGN(len, 4) + sizeof(*hdr));
-
-	mutex_lock(&node->ep_lock);
-	if (node->ep)
-		rc = node->ep->xmit(node->ep, skb);
-	else
-		kfree_skb(skb);
-	mutex_unlock(&node->ep_lock);
+	rc = skb_put_padto(skb, ALIGN(len, 4) + sizeof(*hdr));
 
+	if (!rc) {
+		mutex_lock(&node->ep_lock);
+		rc = -ENODEV;
+		if (node->ep)
+			rc = node->ep->xmit(node->ep, skb);
+		else
+			kfree_skb(skb);
+		mutex_unlock(&node->ep_lock);
+	}
 	/* Need to ensure that a subsequent message carries the otherwise lost
 	 * confirm_rx flag if we dropped this one */
 	if (rc && confirm_rx)