[net v2] tcp: Explicitly mark reserved field in tcp_zerocopy_receive args.

[Arjun Roy]

From: Arjun Roy <arjun...@google.com>

Explicitly define reserved field and require it to be 0-valued.

Fixes: 7eeba1706eba ("tcp: Add receive timestamp support for receive zerocopy.")
Signed-off-by: Arjun Roy <arjun...@google.com>
Signed-off-by: Eric Dumazet <eduma...@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soh...@google.com>
Suggested-by: David Ahern <dsah...@gmail.com>
Suggested-by: Leon Romanovsky <l...@kernel.org>
Suggested-by: Jakub Kicinski <k...@kernel.org>
---
 include/uapi/linux/tcp.h | 2 +-
 net/ipv4/tcp.c           | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
index 42fc5a640df4..8fc09e8638b3 100644
--- a/include/uapi/linux/tcp.h
+++ b/include/uapi/linux/tcp.h
@@ -357,6 +357,6 @@ struct tcp_zerocopy_receive {
        __u64 msg_control; /* ancillary data */
        __u64 msg_controllen;
        __u32 msg_flags;
-       /* __u32 hole;  Next we must add >1 u32 otherwise length checks fail. */
+       __u32 reserved; /* set to 0 for now */
 };
 #endif /* _UAPI_LINUX_TCP_H */
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e1a17c6b473c..c8469c579ed8 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4159,6 +4159,8 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
                }
                if (copy_from_user(&zc, optval, len))
                        return -EFAULT;
+               if (zc.reserved)
+                       return -EINVAL;
                lock_sock(sk);
                err = tcp_zerocopy_receive(sk, &zc, &tss);
                release_sock(sk);
-- 
2.30.0.478.g8a0d178c01-goog