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Message-ID: <18c3aff94ef.7cc78f6896702.921153651485959341@siddh.me>
Date: Tue, 05 Dec 2023 22:51:17 +0530
From: Siddh Raman Pant <code@...dh.me>
To: "Krzysztof Kozlowski" <krzysztof.kozlowski@...aro.org>
Cc: "David S. Miller" <davem@...emloft.net>,
"Eric Dumazet" <edumazet@...gle.com>,
"Jakub Kicinski" <kuba@...nel.org>,
"Paolo Abeni" <pabeni@...hat.com>,
"Suman Ghosh" <sumang@...vell.com>,
"netdev" <netdev@...r.kernel.org>,
"linux-kernel" <linux-kernel@...r.kernel.org>,
"syzbot+bbe84a4010eeea00982d"
<syzbot+bbe84a4010eeea00982d@...kaller.appspotmail.com>
Subject: Re: [PATCH net-next v3 1/2] nfc: llcp_core: Hold a ref to
llcp_local->dev when holding a ref to llcp_local
On Tue, 05 Dec 2023 22:10:00 +0530, Krzysztof Kozlowski wrote:
> > @@ -180,6 +183,7 @@ int nfc_llcp_local_put(struct nfc_llcp_local *local)
> > if (local == NULL)
> > return 0;
> >
> > + nfc_put_device(local->dev);
>
> Mismatched order with get. Unwinding is always in reversed order. Or
> maybe other order is here on purpose? Then it needs to be explained.
Yes, local_release() will free local, so local->dev cannot be accessed.
Will add a comment.
> > @@ -959,8 +963,18 @@ static void nfc_llcp_recv_connect(struct nfc_llcp_local *local,
> > }
> >
> > new_sock = nfc_llcp_sock(new_sk);
> > - new_sock->dev = local->dev;
> > +
> > new_sock->local = nfc_llcp_local_get(local);
> > + if (!new_sock->local) {
>
> There is already an cleanup path/label, so extend it. Existing code
> needs some improvements in that matter as well.
Sure.
> > + reason = LLCP_DM_REJ;
> > + release_sock(&sock->sk);
> > + sock_put(&sock->sk);
> > + sock_put(&new_sock->sk);
> > + nfc_llcp_sock_free(new_sock);
> > + goto fail;
> > + }
> > +
> > + new_sock->dev = local->dev;
> > new_sock->rw = sock->rw;
> > new_sock->miux = sock->miux;
> > new_sock->nfc_protocol = sock->nfc_protocol;
> > @@ -1597,7 +1611,13 @@ int nfc_llcp_register_device(struct nfc_dev *ndev)
> > if (local == NULL)
> > return -ENOMEM;
> >
> > - local->dev = ndev;
> > + /* Hold a reference to the device. */
>
> That's obvious. Instead write something not obvious - why you call
> nfc_get_device() while not incrementing reference to llcp_local.
Should I move it after kref_init()? Here, I'm bailing out early so we
don't have to do unnecessary init first, and the rest of the function
will never fail.
> > + local->dev = nfc_get_device(ndev->idx);
>
> This looks confusing. If you can access ndev->idx, then ndev reference
> was already increased. In such case iterating through all devices to
> find it, is unnecessary and confusing.
I agree, it was something I thought about as well. There should be a
new function for refcount increment. Maybe the existing one could be
renamed to nfc_get_device_from_idx() and a new nfc_get_device() be
defined.
I didn't want to introduce improvement patches in this UAF series, as
that would be an independent unit of change.
Thanks,
Siddh
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