netdev - Re: net/hsr: Question about hsr_port_get_hsr() and possbile null-pointer-dereference

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Message-ID: <20241007100138.643f5c61@wsk>
Date: Mon, 7 Oct 2024 10:01:38 +0200
From: Lukasz Majewski <lukma@...x.de>
To: Zichen Xie <zichenxie0106@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, horms@...nel.org, aleksander.lobakin@...el.com,
 n.zhandarovich@...tech.ru, ricardo@...liere.net, m-karicheri2@...com,
 netdev@...r.kernel.org, Zijie Zhao <zzjas98@...il.com>, Chenyuan Yang
 <chenyuan0y@...il.com>
Subject: Re: net/hsr: Question about hsr_port_get_hsr() and possbile
 null-pointer-dereference

Hi Zichen,

> Dear Developers for NETWORKING [GENERAL],
> 
> We are curious about the function hsr_port_get_hsr().
> The function may return NULL when it cannot find a corresponding port.
> But there is no NULL check in hsr_check_carrier_and_operstate() here:
> https://elixir.bootlin.com/linux/v6.12-rc1/source/net/hsr/hsr_device.c#L93
> The relevant code is:
> ```
> master = hsr_port_get_hsr(hsr, HSR_PT_MASTER);
> /* netif_stacked_transfer_operstate() cannot be used here since
> * it doesn't set IF_OPER_LOWERLAYERDOWN (?)
> */
> has_carrier = hsr_check_carrier(master);
> hsr_set_operstate(master, has_carrier);
> hsr_check_announce(master->dev);
> ```
> There may be possible NULL Pointer Dereference.
> However, in hsr_dev_xmit() the NULL checker exists.

This function is called when NETDEV_UP/DOWN/CHANGE is called for hsr
net device.

IMHO, this cannot be called without having first created hsr network
device (with iproute2 command).

> ```
> master = hsr_port_get_hsr(hsr, HSR_PT_MASTER);
> if (master) {
> skb->dev = master->dev;
> skb_reset_mac_header(skb);
> skb_reset_mac_len(skb);
> spin_lock_bh(&hsr->seqnr_lock);
> hsr_forward_skb(skb, master);
> spin_unlock_bh(&hsr->seqnr_lock);
> } else {
> dev_core_stats_tx_dropped_inc(dev);
> dev_kfree_skb_any(skb);
> }
> ```
> So we are curious if this NULL check is necessary. The function
> hsr_port_get_hsr() is called several times, but NULL checks seem to
> exist occasionally.
> 
> Please kindly correct us if we missed any key information. Looking
> forward to your response!
> 
> Best,
> Zichen




Best regards,

Lukasz Majewski

--

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HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma@...x.de

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