Re: [syzbot] [kvm?] [net?] [virt?] WARNING in virtio_transport_send_pkt_info (2)

[Edward Adam Davis]

#syz test

diff --git a/net/core/datagram.c b/net/core/datagram.c
index c285c6465923..db253fd890d7 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -636,6 +636,8 @@ int zerocopy_fill_skb_from_iter(struct sk_buff *skb,
 				struct iov_iter *from, size_t length)
 {
 	int frag = skb_shinfo(skb)->nr_frags;
+	int err;
+	size_t len = length;
 
 	if (!skb_frags_readable(skb))
 		return -EFAULT;
@@ -647,13 +649,17 @@ int zerocopy_fill_skb_from_iter(struct sk_buff *skb,
 		size_t start;
 		ssize_t copied;
 
-		if (frag == MAX_SKB_FRAGS)
-			return -EMSGSIZE;
+		if (frag == MAX_SKB_FRAGS) {
+			err = -EMSGSIZE;
+			goto fault;
+		}
 
 		copied = iov_iter_get_pages2(from, pages, length,
 					    MAX_SKB_FRAGS - frag, &start);
-		if (copied < 0)
-			return -EFAULT;
+		if (copied < 0) {
+			err = -EFAULT;
+			goto fault;
+		}
 
 		length -= copied;
 
@@ -701,6 +707,9 @@ int zerocopy_fill_skb_from_iter(struct sk_buff *skb,
 			page_ref_sub(last_head, refs);
 	}
 	return 0;
+fault:
+	iov_iter_revert(from, len - length);
+	return err;
 }
 
 static int