linux-kernel - Re: [PATCH AUTOSEL 5.10 10/33] staging: rtl8192e: Fix return type for implementation of ndo_start

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Date:   Tue, 18 Oct 2022 11:48:21 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        GUO Zihua <guozihua@...wei.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        philipp.g.hortmann@...il.com, dave@...olabs.net,
        paskripkin@...il.com, dan.carpenter@...cle.com,
        yogi.kernel@...il.com, yangyingliang@...wei.com,
        f3sch.git@...look.com, linux-staging@...ts.linux.dev
Subject: Re: [PATCH AUTOSEL 5.10 10/33] staging: rtl8192e: Fix return type
 for implementation of ndo_start_xmit

Hi!

> [ Upstream commit 513d9a61156d79dd0979c4ad400c8587f52cbb9d ]
> 
> CFI (Control Flow Integrity) is a safety feature allowing the system to
> detect and react should a potential control flow hijacking occurs. In
> particular, the Forward-Edge CFI protects indirect function calls by
> ensuring the prototype of function that is actually called matches the
> definition of the function hook.
> 
> Since Linux now supports CFI, it will be a good idea to fix mismatched
> return type for implementation of hooks. Otherwise this would get
> cought out by CFI and cause a panic.
> 
> Use enums from netdev_tx_t as return value instead, then change return
> type to netdev_tx_t. Note that rtllib_xmit_inter() would return 1 only
> on allocation failure and the queue is stopped if that happens, meeting
> the documented requirement if NETDEV_TX_BUSY should be returned by
> ndo_start_xmit.
> 

> +++ b/drivers/staging/rtl8192e/rtllib_tx.c
> @@ -964,9 +964,9 @@ static int rtllib_xmit_inter(struct sk_buff *skb, struct net_device *dev)
>  
>  }
>  
> -int rtllib_xmit(struct sk_buff *skb, struct net_device *dev)
> +netdev_tx_t rtllib_xmit(struct sk_buff *skb, struct net_device *dev)
>  {
>  	memset(skb->cb, 0, sizeof(skb->cb));
> -	return rtllib_xmit_inter(skb, dev);
> +	return rtllib_xmit_inter(skb, dev) ? NETDEV_TX_BUSY : NETDEV_TX_OK;
>  }
>  EXPORT_SYMBOL(rtllib_xmit);

First, rtllib_xmit_inter() should be fixed to return the enum, too.

Second, we really should not take this to stable, as CFI is not
available there. We should drop these patches:

 4.19 14/19] staging: rtl8192u: Fix return type of ieee80211_xmit
 5.10 09/33] staging: rtl8712: Fix return type for implementation of ndo_start_xmit
 5.10 10/33] staging: rtl8192e: Fix return type for implementation of ndo_start_xmit

Thank you,
								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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