tcp: make tcp_read_sock() more robust

If recv_actor() returns an incorrect value, tcp_read_sock()
might loop forever.

Instead, issue a one time warning and make sure to make progress.

Signed-off-by: Eric Dumazet <[email protected]>
Acked-by: John Fastabend <[email protected]>
Acked-by: Jakub Sitnicki <[email protected]>
Acked-by: Daniel Borkmann <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: edumazet

net/ipv4/tcp.c

@@ -1684,11 +1684,13 @@ int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
 				if (!copied)
 					copied = used;
 				break;
-			} else if (used <= len) {
-				seq += used;
-				copied += used;
-				offset += used;
 			}
+			if (WARN_ON_ONCE(used > len))
+				used = len;
+			seq += used;
+			copied += used;
+			offset += used;
+
 			/* If recv_actor drops the lock (e.g. TCP splice
 			 * receive) the skb pointer might be invalid when
 			 * getting here: tcp_collapse might have deleted it