linux-kernel - Re: [PATCH 2/3] net: xfrm: unexport __init-annotated xfrm4_protocol

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Date:   Tue, 07 Jun 2022 13:18:32 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Steffen Klassert <steffen.klassert@...unet.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        David Ahern <dsahern@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH 2/3] net: xfrm: unexport __init-annotated
 xfrm4_protocol_init()

On Mon, 2022-06-06 at 13:53 +0900, Masahiro Yamada wrote:
> EXPORT_SYMBOL and __init is a bad combination because the .init.text
> section is freed up after the initialization. Hence, modules cannot
> use symbols annotated __init. The access to a freed symbol may end up
> with kernel panic.
> 
> modpost used to detect it, but it has been broken for a decade.
> 
> Recently, I fixed modpost so it started to warn it again, then this
> showed up in linux-next builds.
> 
> There are two ways to fix it:
> 
>   - Remove __init
>   - Remove EXPORT_SYMBOL
> 
> I chose the latter for this case because the only in-tree call-site,
> net/ipv4/xfrm4_policy.c is never compiled as modular.
> (CONFIG_XFRM is boolean)
> 
> Fixes: 2f32b51b609f ("xfrm: Introduce xfrm_input_afinfo to access the the callbacks properly")
> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

@Steffen: are you ok if we take this one in the -net tree directly?
Otherwise a repost would probably be the better option, with this patch
stand-alone targeting the ipsec tree and the other 2 targeting -net.

Thanks!

Paolo