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

On 2/7/21 10:49 AM, David Ahern wrote:

On 2/6/21 1:36 PM, Arjun Roy wrote:

quoted

From: Arjun Roy <redacted>

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 <redacted>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Soheil Hassas Yeganeh <redacted>
Suggested-by: David Ahern <redacted>
Suggested-by: Leon Romanovsky <leon@kernel.org>
Suggested-by: Jakub Kicinski <kuba@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);

The 'switch (len)' statement needs to be updated now that 'len' is not
going to end on the 'msg_flags' boundary? But then, how did that work
before if there was 4 byte padding?

Maybe I am missing something here. You currently have:

	switch (len) {
	case offsetofend(struct tcp_zerocopy_receive, msg_flags):

Ah, I missed the lines before it:

                if (len >= offsetofend(struct tcp_zerocopy_receive,
msg_flags))
                        goto zerocopy_rcv_cmsg;


Also, I see a check on zc.msg_flags for a specific flag option being
set. What about other invalid bits in msg_flags? I do not see a check like:

#define TCP_VALID_ZC_MSG_FLAGS   (TCP_CMSG_TS)

	if (zc.msg_flags & ~(TCP_VALID_ZC_MSG_FLAGS))
		return -EINVAL;