netdev - Re: [PATCHv2 net] ipv6: sr: fix invalid unregister error path

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Date: Wed, 8 May 2024 11:33:18 +0200
From: Sabrina Dubroca <sd@...asysnail.net>
To: Hangbin Liu <liuhangbin@...il.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	David Ahern <dsahern@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Vasiliy Kovalev <kovalev@...linux.org>,
	Guillaume Nault <gnault@...hat.com>
Subject: Re: [PATCHv2 net] ipv6: sr: fix invalid unregister error path

2024-05-08, 10:55:02 +0800, Hangbin Liu wrote:
> The error path of seg6_init() is wrong in case CONFIG_IPV6_SEG6_LWTUNNEL
> is not defined. In that case if seg6_hmac_init() fails, the
> genl_unregister_family() isn't called.
> 
> At the same time, add seg6_local_exit() and fix the genl unregister order
> in seg6_exit().
> 
> Fixes: 5559cea2d5aa ("ipv6: sr: fix possible use-after-free and null-ptr-deref")
> Reported-by: Guillaume Nault <gnault@...hat.com>
> Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
> ---
> v2: define label out_unregister_genl in CONFIG_IPV6_SEG6_LWTUNNEL(Sabrina Dubroca)
> ---
>  net/ipv6/seg6.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/seg6.c b/net/ipv6/seg6.c
> index 35508abd76f4..6a80d93399ce 100644
> --- a/net/ipv6/seg6.c
> +++ b/net/ipv6/seg6.c
> @@ -551,8 +551,8 @@ int __init seg6_init(void)
>  #endif
>  #ifdef CONFIG_IPV6_SEG6_LWTUNNEL
>  out_unregister_genl:
> -	genl_unregister_family(&seg6_genl_family);
>  #endif
> +	genl_unregister_family(&seg6_genl_family);

Sorry, I didn't notice when you answered my comment yesterday, but
this will create unreachable code after return when
CONFIG_IPV6_SEG6_LWTUNNEL=n and CONFIG_IPV6_SEG6_HMAC=n:

out:
	return err;
	genl_unregister_family(&seg6_genl_family);
out_unregister_pernet:
	unregister_pernet_subsys(&ip6_segments_ops);
	goto out;


(stragely, gcc doesn't complain about it, I thought it would)


The only solution I can think of if we want to avoid it is ugly:

 #ifdef CONFIG_IPV6_SEG6_LWTUNNEL
 out_unregister_genl:
 #endif
+#if IS_ENABLED(CONFIG_IPV6_SEG6_LWTUNNEL) || IS_ENABLED(CONFIG_IPV6_SEG6_HMAC)
 	genl_unregister_family(&seg6_genl_family);
+#endif
 out_unregister_pernet:
 	unregister_pernet_subsys(&ip6_segments_ops);
 	goto out;

(on top of v2)

For all other cases your patch looks correct.

-- 
Sabrina