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Subject: Re: Query on possible bug in the can_create_echo_skb() API
To:     Srinivas Neeli <sneeli@xilinx.com>,
        "wg@grandegger.com" <wg@grandegger.com>
Cc:     Srinivas Goud <sgoud@xilinx.com>,
        Naga Sureshkumar Relli <nagasure@xilinx.com>,
        Appana Durga Kedareswara Rao <appanad@xilinx.com>,
        "linux-can@vger.kernel.org" <linux-can@vger.kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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From:   Marc Kleine-Budde <mkl@pengutronix.de>
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Message-ID: <3a8c557f-adb5-144d-00f1-1b1c608129dc@pengutronix.de>
Date:   Wed, 28 Aug 2019 14:15:51 +0200
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From: Marc Kleine-Budde <mkl@pengutronix.de>
To: Srinivas Neeli <sneeli@xilinx.com>, "wg@grandegger.com"
 <wg@grandegger.com>
Cc: Srinivas Goud <sgoud@xilinx.com>,
 Naga Sureshkumar Relli <nagasure@xilinx.com>,
 Appana Durga Kedareswara Rao <appanad@xilinx.com>,
 "linux-can@vger.kernel.org" <linux-can@vger.kernel.org>,
 "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
 "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Message-ID: <3a8c557f-adb5-144d-00f1-1b1c608129dc@pengutronix.de>
Subject: Re: Query on possible bug in the can_create_echo_skb() API
References: <BYAPR02MB5464DC9DA2D38AF1100A5A8FAFAA0@BYAPR02MB5464.namprd02.prod.outlook.com>
 <6bd3a657-dd8a-03a5-1e7c-bac532008f6e@pengutronix.de>
 <BYAPR02MB546403642B2233DDD5C456C4AFA30@BYAPR02MB5464.namprd02.prod.outlook.com>
In-Reply-To: <BYAPR02MB546403642B2233DDD5C456C4AFA30@BYAPR02MB5464.namprd02.prod.outlook.com>

--RY22PpBUTD32uM4bOZ1jQik2RlJaeGTmM
Content-Type: text/plain; charset=utf-8
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On 8/28/19 1:02 PM, Srinivas Neeli wrote:
> Case 1:
> can_put_echo_skb(); -> skb =3D can_create_echo_skb(skb); -> return skb;=

>=20
> In can_create_echo_skb() not using the shared_skb, so we are returning =
the old skb.
> Storing the return value in "skb". But it's a pointer, for storing that=
 need double pointer.
> Instead of double-pointer using a single pointer. In this scenario it's=
 ok , we are returning the same SKB.
>=20
> Case 2:
> can_put_echo_skb(skb, ndev, priv->tx_head % priv->tx_max); -> skb =3D c=
an_create_echo_skb(skb); -> can_skb_set_owner(nskb, skb->sk); - Returning=
 nskb;
>=20
> shared_skb scenario:
> In share-skb case =E2=80=9Ccan_create_echo_skb(skb);=E2=80=9D  returnin=
g "new skb". For storing new skb need a double pointer.
>=20
> Providing an example for overcoming above issue.
> Example:
> can_put_echo_skb(struct sk_buff **skb,struct net_device *dev,unsigned i=
nt idx);

Now I get what you mean.

> If you ok with this change, I will send a patch.

I think the can_put_echo_skb() API needs clarification. The driver is
not allowed to touch the skb any more after can_put_echo_skb(). We
should review the driver for this.

thanks,
Marc

--=20
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |


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