[PATCH net v2 6/7] net/handshake: Close the submit-side sock_hold race

From: Chuck Lever <[email protected]>

handshake_req_submit() publishes the request via
handshake_req_hash_add() and __add_pending_locked(), drops
hn_lock, and calls handshake_genl_notify() (which can sleep)
before taking sock_hold() on req->hr_sk. A fast tlshd ACCEPT
followed by DONE can drive handshake_complete()'s sock_put()
into the window between the spin_unlock and the late
sock_hold(); on a system where the consumer's fd held the
only sk reference, the late sock_hold() then operates on an
sk whose refcount has reached zero.

The preceding two patches install an explicit file reference
on struct handshake_req. That file pins sock->file, which
pins the embedded struct socket, which defers inet_release()'s
sock_put(). As long as hr_file is held, sk cannot reach refcount
zero from the consumer side, and the submit-side sock_hold()
with its matching sock_put() calls in handshake_complete() and
handshake_req_cancel() is now redundant.

Drop all three. Submit's pinning is strictly the file reference
acquired earlier in the function, and the lifetime story is
contained in a single get_file()/fput() pair.

Fixes: 3b3009ea8abb ("net/handshake: Create a NETLINK service for handling handshake requests")
Signed-off-by: Chuck Lever <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
---
 net/handshake/request.c | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/net/handshake/request.c b/net/handshake/request.c
index d24b55af1a0a..1c669c1602b5 100644
--- a/net/handshake/request.c
+++ b/net/handshake/request.c
@@ -301,13 +301,6 @@ int handshake_req_submit(struct socket *sock, struct handshake_req *req,
 			goto out_err;
 	}
 
-	/*
-	 * Pin struct sock so sk_destruct does not run until the
-	 * handshake completion path releases it; struct socket is
-	 * held separately via hr_file above.
-	 */
-	sock_hold(req->hr_sk);
-
 	trace_handshake_submit(net, req, req->hr_sk);
 	return 0;
 
@@ -335,9 +328,6 @@ void handshake_complete(struct handshake_req *req, int status,
 		trace_handshake_complete(net, req, sk, status);
 		req->hr_proto->hp_done(req, status, info);
 
-		/* Handshake request is no longer pending */
-		sock_put(sk);
-
 		fput(file);
 	}
 }
@@ -385,8 +375,6 @@ bool handshake_req_cancel(struct sock *sk)
 out_true:
 	trace_handshake_cancel(net, req, sk);
 
-	/* Handshake request is no longer pending */
-	sock_put(sk);
 	fput(req->hr_file);
 	return true;
 }

-- 
2.54.0