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From:   Siddh Raman Pant <code@siddh.me>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        Samuel Ortiz <sameo@linux.intel.com>
Subject: [PATCH net-next v2 0/2] nfc: Fix UAF during datagram sending caused by missing refcounting
Date:   Sat,  2 Dec 2023 21:10:57 +0530
Message-ID: <cover.1701530776.git.code@siddh.me>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

For connectionless transmission, llcp_sock_sendmsg() codepath will
eventually call nfc_alloc_send_skb() which takes in an nfc_dev as
an argument for calculating the total size for skb allocation.

virtual_ncidev_close() codepath eventually releases socket by calling
nfc_llcp_socket_release() (which sets the sk->sk_state to LLCP_CLOSED)
and afterwards the nfc_dev will be eventually freed.

When an ndev gets freed, llcp_sock_sendmsg() will result in an
use-after-free as it

(1) doesn't have any checks in place for avoiding the datagram sending.

(2) calls nfc_llcp_send_ui_frame(), which also has a do-while loop
    which can race with freeing. This loop contains the call to
    nfc_alloc_send_skb() where we dereference the nfc_dev pointer.

nfc_dev is being freed because we do not hold a reference to it when
we hold a reference to llcp_local. Thus, virtual_ncidev_close()
eventually calls nfc_release() due to refcount going to 0.

Since state has to be LLCP_BOUND for datagram sending, we can bail out
early in llcp_sock_sendmsg().

Please review and let me know if any errors are there, and hopefully
this gets accepted.

Thanks,
Siddh

Changes in v2:
- Add net-next in patch subject.
- Removed unnecessary extra lock and hold nfc_dev ref when holding llcp_sock.
- Remove last formatting patch.
- Picked up r-b from Krzysztof for LLCP_BOUND patch.

Siddh Raman Pant (2):
  nfc: llcp_core: Hold a ref to llcp_local->dev when holding a ref to
    llcp_local
  nfc: Do not send datagram if socket state isn't LLCP_BOUND

 net/nfc/llcp_core.c | 21 +++++++++++++++++++--
 net/nfc/llcp_sock.c |  5 +++++
 2 files changed, 24 insertions(+), 2 deletions(-)

-- 
2.42.0