[PATCH v1] net: Add distinct sk_psock field

From: Chuck Lever
Date: Wed Jul 13 2022 - 10:26:34 EST

The sk_psock facility populates the sk_user_data field with the
address of an extra bit of metadata. User space sockets never
populate the sk_user_data field, so this has worked out fine.

However, kernel socket consumers such as the RPC client and server
do populate the sk_user_data field. The sk_psock() function cannot
tell that the content of sk_user_data does not point to psock
metadata, so it will happily return a pointer to something else,
cast to a struct sk_psock.

Thus kernel socket consumers and psock currently cannot co-exist.

We could educate sk_psock() to return NULL if sk_user_data does
not point to a struct sk_psock. However, a more general solution
that enables full co-existence psock and other uses of sk_user_data
might be more interesting.

Move the struct sk_psock address to its own pointer field so that
the contents of the sk_user_data field is preserved.

Reviewed-by: Hannes Reinecke <hare@xxxxxxx>
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
include/linux/skmsg.h | 2 +-
include/net/sock.h | 4 +++-
net/core/skmsg.c | 6 +++---
3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
index c5a2d6f50f25..5ef3a07c5b6c 100644
--- a/include/linux/skmsg.h
+++ b/include/linux/skmsg.h
@@ -277,7 +277,7 @@ static inline void sk_msg_sg_copy_clear(struct sk_msg *msg, u32 start)

static inline struct sk_psock *sk_psock(const struct sock *sk)
- return rcu_dereference_sk_user_data(sk);
+ return rcu_dereference(sk->sk_psock);

static inline void sk_psock_set_state(struct sk_psock *psock,
diff --git a/include/net/sock.h b/include/net/sock.h
index c4b91fc19b9c..d2a513169527 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -327,7 +327,8 @@ struct sk_filter;
* @sk_tskey: counter to disambiguate concurrent tstamp requests
* @sk_zckey: counter to order MSG_ZEROCOPY notifications
* @sk_socket: Identd and reporting IO signals
- * @sk_user_data: RPC layer private data
+ * @sk_user_data: Upper layer private data
+ * @sk_psock: socket policy data (bpf)
* @sk_frag: cached page frag
* @sk_peek_off: current peek_offset value
* @sk_send_head: front of stuff to transmit
@@ -519,6 +520,7 @@ struct sock {

struct socket *sk_socket;
void *sk_user_data;
+ struct sk_psock __rcu *sk_psock;
void *sk_security;
diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index cc381165ea08..2b3d01d92790 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -695,7 +695,7 @@ struct sk_psock *sk_psock_init(struct sock *sk, int node)


- if (sk->sk_user_data) {
+ if (sk->sk_psock) {
psock = ERR_PTR(-EBUSY);
goto out;
@@ -726,7 +726,7 @@ struct sk_psock *sk_psock_init(struct sock *sk, int node)
sk_psock_set_state(psock, SK_PSOCK_TX_ENABLED);
refcount_set(&psock->refcnt, 1);

- rcu_assign_sk_user_data_nocopy(sk, psock);
+ rcu_assign_pointer(sk->sk_psock, psock);

@@ -825,7 +825,7 @@ void sk_psock_drop(struct sock *sk, struct sk_psock *psock)
sk_psock_restore_proto(sk, psock);
- rcu_assign_sk_user_data(sk, NULL);
+ rcu_assign_pointer(sk->sk_psock, NULL);
if (psock->progs.stream_parser)
sk_psock_stop_strp(sk, psock);
else if (psock->progs.stream_verdict || psock->progs.skb_verdict)