kcm: fix strp_init() order and cleanup

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@syzkaller.appspotmail.com
Reported-by: syzbot+e696806ef96cdd2d87cd@syzkaller.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: Tom Herbert <tom@herbertland.com>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Link: https://lore.kernel.org/r/20220827181314.193710-1-xiyou.wangcong@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 71899e5..1215c86 100644 (file)
--- 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;