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Subject: Re: [PATCH] wifi: mac80211: sband's null check should precede params
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Edward Adam Davis <eadavis@qq.com>
Cc:     davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
        linux-kernel@vger.kernel.org, linux-wireless@vger.kernel.org,
        llvm@lists.linux.dev, nathan@kernel.org, ndesaulniers@google.com,
        netdev@vger.kernel.org, pabeni@redhat.com,
        syzbot+62d7eef57b09bfebcd84@syzkaller.appspotmail.com,
        syzkaller-bugs@googlegroups.com, trix@redhat.com
Date:   Wed, 29 Nov 2023 10:15:03 +0100
In-Reply-To: <tencent_6E9CA7EF46E452C90650899D2ECFEEFE4C06@qq.com>
References: <56d8b3b9099d3935a7b53e976fa998f06fbfd9a5.camel@sipsolutions.net>
         <tencent_6E9CA7EF46E452C90650899D2ECFEEFE4C06@qq.com>
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On Wed, 2023-11-29 at 16:48 +0800, Edward Adam Davis wrote:
> On Wed, 29 Nov 2023 09:33:23 +0100, Johannes Berg wrote:
> > > > > [Analysis]
> > > > > When ieee80211_get_link_sband() fails to find a valid sband and f=
irst checks
> > > > > for params in sta_link_apply_parameters(), it will return 0 due t=
o new_link
> > > > > being 0, which will lead to an incorrect process after sta_apply_=
parameters().
> > > > >=20
> > > > > [Fix]
> > > > > First obtain sband and perform a non null check before checking t=
he params.
> > > >=20
> > > > Not sure I can even disagree with that analysis, it seems right, bu=
t ...
> > > >=20
> > > > > +	if (!link || !link_sta)
> > > > > +		return -EINVAL;
> > > > > +
> > > > > +	sband =3D ieee80211_get_link_sband(link);
> > > > > +	if (!sband)
> > > > > +		return -EINVAL;
> > > > > +
> > > > >  	/*
> > > > >  	 * If there are no changes, then accept a link that doesn't exi=
st,
> > > > >  	 * unless it's a new link.
> > > >=20
> > > > There's a comment here which is clearly not true after this change,
> > > > since you've already returned for !link_sta?
> > > No, after applying my patch, it will return due to !sband.
> > >=20
> >=20
> > Right, OK, but the way I read the comment (now) is that it wanted to
> > accept it in that case?
> >=20
> > That said, I just threw the patch into our internal testing machinery
> > quickly (probably has more MLO tests than upstream hostap for now), and
> > it worked just fine ...
> >=20
> > Maybe we should just remove the comment?
> Do you mean to delete the comments below?
>    3         /*
>    2          * If there are no changes, then accept a link that doesn't =
exist,
>    1          * unless it's a new link.
> 1800          */
>=20

Right, it doesn't seem correct any more?

johannes