linux-kernel - Re: [PATCH RFC 3/5] rtnetlink: do_setlink: Use sockaddr

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Message-ID: <202412161749.84F7671F3@keescook>
Date: Mon, 16 Dec 2024 17:52:31 -0800
From: Kees Cook <kees@...nel.org>
To: Eric Dumazet <eric.dumazet@...il.com>
Cc: Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH RFC 3/5] rtnetlink: do_setlink: Use sockaddr_storage

On Tue, Nov 05, 2024 at 11:59:49AM +0100, Eric Dumazet wrote:
> 
> On 11/4/24 11:25 PM, Kees Cook wrote:
> > Instead of a heap allocation use a stack allocated sockaddr_storage to
> > support arbitrary length addr_len value (but bounds check it against the
> > maximum address length).
> > 
> > Signed-off-by: Kees Cook <kees@...nel.org>
> > ---
> >   net/core/rtnetlink.c | 12 ++++--------
> >   1 file changed, 4 insertions(+), 8 deletions(-)
> > 
> > diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> > index f0a520987085..eddd10b74f06 100644
> > --- a/net/core/rtnetlink.c
> > +++ b/net/core/rtnetlink.c
> > @@ -2839,21 +2839,17 @@ static int do_setlink(const struct sk_buff *skb,
> >   	}
> >   	if (tb[IFLA_ADDRESS]) {
> > -		struct sockaddr *sa;
> > -		int len;
> > +		struct sockaddr_storage addr;
> > +		struct sockaddr *sa = (struct sockaddr *)&addr;
> 
> We already use too much stack space.

I'm finally coming back to this. I was over-thinking: this only calls
dev_set_mac_address_user() so it really is a true struct sockaddr.

> Please move addr into struct rtnl_newlink_tbs ?

I couldn't figure out how that was meant to work -- I didn't see a
struct rtnl_newlink_tbs instance near this routine.

Regardless, I can just tweak the length and leave it heap allocated.

-Kees

-- 
Kees Cook