linux-kernel - Re: [PATCH 5.10 09/38] llc: fix netdevice reference leaks in llc_ui

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Date:   Sat, 26 Mar 2022 21:09:22 +0100
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Eric Dumazet <edumazet@...gle.com>,
        赵子轩 <beraphin@...il.com>,
        Stoyan Manolov <smanolov@...e.de>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH 5.10 09/38] llc: fix netdevice reference leaks in
 llc_ui_bind()

Hi!

> From: Eric Dumazet <edumazet@...gle.com>
> 
> commit 764f4eb6846f5475f1244767d24d25dd86528a4a upstream.
> 
> Whenever llc_ui_bind() and/or llc_ui_autobind()
> took a reference on a netdevice but subsequently fail,
> they must properly release their reference
> or risk the infamous message from unregister_netdevice()
> at device dismantle.
> 
> unregister_netdevice: waiting for eth0 to become free. Usage count =
> 3

Can someone check this? AFAICT this is buggy.

static int llc_ui_autobind(struct socket *sock, struct sockaddr_llc *addr)
{
        struct sock *sk = sock->sk;
        struct llc_sock *llc = llc_sk(sk);
        struct llc_sap *sap;
        int rc = -EINVAL;

        if (!sock_flag(sk, SOCK_ZAPPED))
                goto out;

There are 'goto out's from both before dev_get() and after it,
dev_put() will be called with NULL pointer. dev_put() can't handle
NULL at least in the old kernels... this is simply confused.

Mainline has dev_put_track() there, but I see same confusion.

Best regards,
								Pavel


> --- a/net/llc/af_llc.c
> +++ b/net/llc/af_llc.c
> @@ -311,6 +311,10 @@ static int llc_ui_autobind(struct socket
>  	sock_reset_flag(sk, SOCK_ZAPPED);
>  	rc = 0;
>  out:
> +	if (rc) {
> +		dev_put(llc->dev);
> +		llc->dev = NULL;
> +	}
>  	return rc;
>  }
>  
> @@ -409,6 +413,10 @@ static int llc_ui_bind(struct socket *so
>  out_put:
>  	llc_sap_put(sap);
>  out:
> +	if (rc) {
> +		dev_put(llc->dev);
> +		llc->dev = NULL;
> +	}
>  	release_sock(sk);
>  	return rc;
>  }
> 

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


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