netdev - [Patch net v2] kcm: fix strp_init() order and cleanup

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Date:   Sat, 27 Aug 2022 11:13:14 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     Cong Wang <cong.wang@...edance.com>,
        syzbot+9fc084a4348493ef65d2@...kaller.appspotmail.com,
        syzbot+e696806ef96cdd2d87cd@...kaller.appspotmail.com,
        Jakub Kicinski <kuba@...nel.org>,
        Tom Herbert <tom@...bertland.com>
Subject: [Patch net v2] kcm: fix strp_init() order and cleanup

From: Cong Wang <cong.wang@...edance.com>

strp_init() is called just a few lines above this csk->sk_user_data
check, it also initializes strp->work etc., therefore, it is
unnecessary to call strp_done() to cancel the freshly initialized
work.

And if sk_user_data is already used by KCM, psock->strp should not be
touched, particularly strp->work state, so we need to move strp_init()
after the csk->sk_user_data check.

This also makes a lockdep warning reported by syzbot go away.

Reported-and-tested-by: syzbot+9fc084a4348493ef65d2@...kaller.appspotmail.com
Reported-by: syzbot+e696806ef96cdd2d87cd@...kaller.appspotmail.com
Fixes: e5571240236c ("kcm: Check if sk_user_data already set in kcm_attach")
Fixes: dff8baa26117 ("kcm: Call strp_stop before strp_done in kcm_attach")
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: Tom Herbert <tom@...bertland.com>
Signed-off-by: Cong Wang <cong.wang@...edance.com>
---
 net/kcm/kcmsock.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 71899e5a5a11..1215c863e1c4 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1412,12 +1412,6 @@ static int kcm_attach(struct socket *sock, struct socket *csock,
 	psock->sk = csk;
 	psock->bpf_prog = prog;
 
-	err = strp_init(&psock->strp, csk, &cb);
-	if (err) {
-		kmem_cache_free(kcm_psockp, psock);
-		goto out;
-	}
-
 	write_lock_bh(&csk->sk_callback_lock);
 
 	/* Check if sk_user_data is already by KCM or someone else.
@@ -1425,13 +1419,18 @@ static int kcm_attach(struct socket *sock, struct socket *csock,
 	 */
 	if (csk->sk_user_data) {
 		write_unlock_bh(&csk->sk_callback_lock);
-		strp_stop(&psock->strp);
-		strp_done(&psock->strp);
 		kmem_cache_free(kcm_psockp, psock);
 		err = -EALREADY;
 		goto out;
 	}
 
+	err = strp_init(&psock->strp, csk, &cb);
+	if (err) {
+		write_unlock_bh(&csk->sk_callback_lock);
+		kmem_cache_free(kcm_psockp, psock);
+		goto out;
+	}
+
 	psock->save_data_ready = csk->sk_data_ready;
 	psock->save_write_space = csk->sk_write_space;
 	psock->save_state_change = csk->sk_state_change;
-- 
2.34.1