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From: Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date: Wed, 6 Dec 2023 09:48:59 -0500
Message-ID: <CABBYNZ+Bnva7CCz3ds25Qx4xnbduXTdSX_FgXAttWSmSuYJadQ@mail.gmail.com>
Subject: Re: [PATCH] Bluetooth: af_bluetooth: Fix Use-After-Free in bt_sock_recvmsg
To: Hyunwoo Kim <v4bel@theori.io>
Cc: marcel@holtmann.org, imv4bel@gmail.com, johan.hedberg@gmail.com, 
	linux-bluetooth@vger.kernel.org
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Hi Kim,

On Mon, Dec 4, 2023 at 2:02=E2=80=AFAM Hyunwoo Kim <v4bel@theori.io> wrote:
>
> This can cause a race with bt_sock_ioctl() because
> bt_sock_recvmsg() gets the skb from sk->sk_receive_queue
> and then frees it without holding lock_sock.
> A use-after-free for a skb occurs with the following flow.
> ```
> bt_sock_recvmsg() -> skb_recv_datagram() -> skb_free_datagram()
> bt_sock_ioctl() -> skb_peek()
> ```
> Add lock_sock to bt_sock_recvmsg() to fix this issue.
>
> Signed-off-by: Hyunwoo Kim <v4bel@theori.io>
> ---
>  net/bluetooth/af_bluetooth.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/net/bluetooth/af_bluetooth.c b/net/bluetooth/af_bluetooth.c
> index 336a76165454..9def13ac816e 100644
> --- a/net/bluetooth/af_bluetooth.c
> +++ b/net/bluetooth/af_bluetooth.c
> @@ -309,11 +309,16 @@ int bt_sock_recvmsg(struct socket *sock, struct msg=
hdr *msg, size_t len,
>         if (flags & MSG_OOB)
>                 return -EOPNOTSUPP;
>
> +       lock_sock(sk);
> +
>         skb =3D skb_recv_datagram(sk, flags, &err);
>         if (!skb) {
> -               if (sk->sk_shutdown & RCV_SHUTDOWN)
> +               if (sk->sk_shutdown & RCV_SHUTDOWN) {
> +                       release_sock(sk);

We could just reset the with err =3D 0 then we don't need to duplicate
the release_sock line.

>                         return 0;
> +               }
>
> +               release_sock(sk);
>                 return err;
>         }
>
> @@ -343,6 +348,8 @@ int bt_sock_recvmsg(struct socket *sock, struct msghd=
r *msg, size_t len,
>
>         skb_free_datagram(sk, skb);
>
> +       release_sock(sk);
> +
>         if (flags & MSG_TRUNC)
>                 copied =3D skblen;
>
> --
> 2.25.1
>


--=20
Luiz Augusto von Dentz