netdev - Re: [PATCH] NET:AX25:ROSE NULL ax25

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Date:   Thu, 24 Jan 2019 18:30:24 +0100
From:   Bernard Pidoux <f6bvp@...e.fr>
To:     linux-hams <linux-hams@...r.kernel.org>
Cc:     Ralf Baechle <ralf@...ux-mips.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        David Miller <davem@...emloft.net>,
        Linux Netdev List <netdev@...r.kernel.org>,
        n1uro@...ro.ampr.org, f6bvp <f6bvp@...e.fr>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH] NET:AX25:ROSE NULL ax25_cb kernel panic

> [PATCH] [ROSE] NULL ax25_cb kernel panic
>
> When an internally generated frame is handled by rose_xmit(),
> rose_route_frame() is called:
>
>          if (!rose_route_frame(skb, NULL)) {
>                  dev_kfree_skb(skb);
>                  stats->tx_errors++;
>                  return NETDEV_TX_OK;
>          }
>
> We have the same code sequence in Net/Rom where an internally generated
> frame is handled by nr_xmit() calling nr_route_frame(skb, NULL).
> However, in this function NULL argument is tested while it is not in
> rose_route_frame().
> Then kernel panic occurs later on when calling ax25cmp() with a NULL
> ax25_cb argument as reported many times and recently with syzbot.
>
> We need to test if ax25 is NULL before using it.
>
> Here is the patch:
>
> diff --git a/net/rose/rose_route.c b/net/rose/rose_route.c
> index 77e9f85a2c92..7f075255a372 100644
> --- a/net/rose/rose_route.c
> +++ b/net/rose/rose_route.c
> @@ -850,6 +850,7 @@ void rose_link_device_down(struct net_device *dev)
>
>   /*
>    *	Route a frame to an appropriate AX.25 connection.
> + *	a NULL ax25_cb indicates an internally generated frame.
>    */
>   int rose_route_frame(struct sk_buff *skb, ax25_cb *ax25)
>   {
> @@ -867,6 +868,10 @@ int rose_route_frame(struct sk_buff *skb, ax25_cb
> *ax25)
>
>   	if (skb->len < ROSE_MIN_LEN)
>   		return res;
> +
> +	if (!ax25)
> +		return rose_loopback_queue(skb, NULL);
> +
>   	frametype = skb->data[2];
>   	lci = ((skb->data[0] << 8) & 0xF00) + ((skb->data[1] << 0) & 0x0FF);
>   	if (frametype == ROSE_CALL_REQUEST &&
> Reported-by:syzbot+1a2c456a1ea08fa5b5f7@...kaller.appspotmail.com
> Signed-off-by: Bernard Pidoux, f6bvp <f6bvp@...e.fr>