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Message-ID: <87ilmf9zha.fsf@cloudflare.com> Date: Fri, 26 Aug 2022 10:32:22 +0200 From: Jakub Sitnicki <jakub@...udflare.com> To: Paolo Abeni <pabeni@...hat.com> Cc: netdev@...r.kernel.org, kernel-team@...udflare.com, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Tom Parkin <tparkin@...alix.com>, Haowei Yan <g1042620637@...il.com> Subject: Re: [PATCH net v3] l2tp: Serialize access to sk_user_data with sk_callback_lock On Thu, Aug 25, 2022 at 12:23 PM +02, Paolo Abeni wrote: > hello, > > On Tue, 2022-08-23 at 12:14 +0200, Jakub Sitnicki wrote: >> sk->sk_user_data has multiple users, which are not compatible with each >> other. Writers must synchronize by grabbing the sk->sk_callback_lock. >> >> l2tp currently fails to grab the lock when modifying the underlying tunnel >> socket. Fix it by adding appropriate locking. >> >> We don't to grab the lock when l2tp clears sk_user_data, because it happens >> only in sk->sk_destruct, when the sock is going away. > > l2tp can additionally clears sk_user_data in sk->sk_prot->close() via > udp_lib_close() -> sk_common_release() -> sk->sk_prot->destroy() -> > udp_destroy_sock() -> up->encap_destroy() -> l2tp_udp_encap_destroy(). > > That still happens at socket closing time, but when network has still > access to the sock itself. It should be safe as the other sk_user_data > users touch it only via fd, but perhaps a 'better safe the sorry' > approach could be relevant there? Fair point. Let me add that.
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