[PATCH net-next] tcp-zerocopy: Update returned getsockopt() optlen.

[Arjun Roy <arjunroy.kdev@gmail.com>]

From: Arjun Roy <arjunroy@google.com>

TCP receive zerocopy currently does not update the returned optlen for
getsockopt(). Thus, userspace cannot properly determine if all the
fields are set in the passed-in struct. This patch sets the optlen
before return, in keeping with the expected operation of getsockopt().

Signed-off-by: Arjun Roy <arjunroy@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>

---
 net/ipv4/tcp.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 600deb39f17de..fb9894d3d30e9 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4148,8 +4148,12 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
 zerocopy_rcv_inq:
 		zc.inq = tcp_inq_hint(sk);
 zerocopy_rcv_out:
-		if (!err && copy_to_user(optval, &zc, len))
-			err = -EFAULT;
+		if (!err) {
+			if (put_user(len, optlen))
+				return -EFAULT;
+			if (copy_to_user(optval, &zc, len))
+				return -EFAULT;
+		}
 		return err;
 	}
 #endif
-- 
2.25.0.265.gbab2e86ba0-goog