netdev - [PATCH bpf] net, sk_msg: Don't use RCU_INIT_POINTER on sk_user

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Message-Id: <20200402125524.851439-1-jakub@cloudflare.com>
Date:   Thu,  2 Apr 2020 14:55:24 +0200
From:   Jakub Sitnicki <jakub@...udflare.com>
To:     bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org, kernel-team@...udflare.com,
        Daniel Borkmann <daniel@...earbox.net>,
        kbuild test robot <lkp@...el.com>
Subject: [PATCH bpf] net, sk_msg: Don't use RCU_INIT_POINTER on sk_user_data

sparse reports an error due to use of RCU_INIT_POINTER helper to assign to
sk_user_data pointer, which is not tagged with __rcu:

net/core/sock.c:1875:25: error: incompatible types in comparison expression (different address spaces):
net/core/sock.c:1875:25:    void [noderef] <asn:4> *
net/core/sock.c:1875:25:    void *

... and rightfully so. sk_user_data is not always treated as a pointer to
an RCU-protected data. When it is used to point at an RCU-protected object,
we access it with __sk_user_data to inform sparse about it.

In this case, when the child socket does not inherit sk_user_data from the
parent, there is no reason to treat it as an RCU-protected pointer.

Use a regular assignment to clear the pointer value.

Fixes: f1ff5ce2cd5e ("net, sk_msg: Clear sk_user_data pointer on clone if tagged")
Reported-by: kbuild test robot <lkp@...el.com>
Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
---
 net/core/sock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/sock.c b/net/core/sock.c
index da32d9b6d09f..0510826bf860 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1872,7 +1872,7 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
 		 * as not suitable for copying when cloning.
 		 */
 		if (sk_user_data_is_nocopy(newsk))
-			RCU_INIT_POINTER(newsk->sk_user_data, NULL);
+			newsk->sk_user_data = NULL;
 
 		newsk->sk_err	   = 0;
 		newsk->sk_err_soft = 0;
-- 
2.25.1