From: Jakub Kicinski <kuba@kernel.org>
To: Lee Jones <lee@kernel.org>
Cc: James Chapman <jchapman@katalix.com>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Paolo Abeni <pabeni@redhat.com>, Simon Horman <horms@kernel.org>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] l2tp: pppol2tp: hold reference to session in pppol2tp_ioctl()
Date: Fri, 22 May 2026 11:14:50 -0700 [thread overview]
Message-ID: <20260522111450.19472919@kernel.org> (raw)
In-Reply-To: <20260520134837.2780050-1-lee@kernel.org>
On Wed, 20 May 2026 14:48:36 +0100 Lee Jones wrote:
> pppol2tp_ioctl() read sock->sk->sk_user_data directly without any locks
> or reference counting. If a controllable sleep was induced during
> copy_from_user() (e.g. via a userfaultfd page fault sleep), a concurrent
> socket close could trigger pppol2tp_session_close() asynchronously. This
> frees the l2tp_session structure via the l2tp_session_del_work workqueue.
> Upon resuming, the ioctl thread dereferences the stale session pointer,
> resulting in a Use-After-Free (UAF).
>
> Fix this by securely fetching the session reference using the RCU-safe,
> refcounted helper pppol2tp_sock_to_session(sk) on entry. This locks the
> session's refcount across the sleep. We structured the function to exit
> via standard err breaks, guaranteeing that l2tp_session_put() is cleanly
> called on all return paths to drop the reference.
Since this is a fix we will need this reposted with a Fixes tag, please.
--
pw-bot: cr
next prev parent reply other threads:[~2026-05-22 18:14 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-20 13:48 [PATCH 1/1] l2tp: pppol2tp: hold reference to session in pppol2tp_ioctl() Lee Jones
2026-05-22 18:14 ` Jakub Kicinski [this message]
2026-05-22 18:15 ` Jakub Kicinski
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