linux-kernel - Re: [PATCH] xfrm6_tunnel: Fix potential panic when unloading xfrm6

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Message-ID: <20190315062438.id3664ccow5uxgvt@gondor.apana.org.au>
Date:   Fri, 15 Mar 2019 14:24:38 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Su Yanjun <suyj.fnst@...fujitsu.com>
Cc:     steffen.klassert@...unet.com, davem@...emloft.net,
        kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH] xfrm6_tunnel: Fix potential panic when unloading
 xfrm6_tunnel module

On Thu, Mar 14, 2019 at 02:59:42PM +0800, Su Yanjun wrote:
> When unloading xfrm6_tunnel module, xfrm6_tunnel_fini directly
> frees the xfrm6_tunnel_spi_kmem. Maybe someone has gotten the
> xfrm6_tunnel_spi, so need to wait it.
> 
> Fixes: 91cc3bb0b04ff("xfrm6_tunnel: RCU conversion")
> Signed-off-by: Su Yanjun <suyj.fnst@...fujitsu.com>
> ---
>  net/ipv6/xfrm6_tunnel.c | 4 ++++
>  1 file changed, 4 insertions(+)

This looks good to me.  And it's not just the matter of accessing
freed memory.  A worse problem would be trying to execute code
from an unloaded module.

Acked-by: Herbert Xu <herbert@...dor.apana.org.au>

> diff --git a/net/ipv6/xfrm6_tunnel.c b/net/ipv6/xfrm6_tunnel.c
> index bc65db7..12cb3aa 100644
> --- a/net/ipv6/xfrm6_tunnel.c
> +++ b/net/ipv6/xfrm6_tunnel.c
> @@ -402,6 +402,10 @@ static void __exit xfrm6_tunnel_fini(void)
>  	xfrm6_tunnel_deregister(&xfrm6_tunnel_handler, AF_INET6);
>  	xfrm_unregister_type(&xfrm6_tunnel_type, AF_INET6);
>  	unregister_pernet_subsys(&xfrm6_tunnel_net_ops);
> +	/* Someone maybe has gotten the xfrm6_tunnel_spi.
> +	 * So need to wait it.
> +	 */
> +	rcu_barrier();
>  	kmem_cache_destroy(xfrm6_tunnel_spi_kmem);
>  }

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt