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Date: Wed, 28 Feb 2024 12:39:42 -0800
From: Kees Cook <keescook@chromium.org>
To: Dominique Martinet <asmadeus@codewreck.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, stable@vger.kernel.org,
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Subject: Re: [PATCH 5.10 000/122] 5.10.211-rc1 review
Message-ID: <202402281231.F7A20FCE@keescook>
References: <20240227131558.694096204@linuxfoundation.org>
 <Zd53aNc1aFrCYxFd@codewreck.org>
 <2024022804-askew-stung-cba8@gregkh>
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In-Reply-To: <2024022804-askew-stung-cba8@gregkh>

On Wed, Feb 28, 2024 at 07:06:38AM +0100, Greg Kroah-Hartman wrote:
> On Wed, Feb 28, 2024 at 08:59:36AM +0900, Dominique Martinet wrote:
> > Greg Kroah-Hartman wrote on Tue, Feb 27, 2024 at 02:26:01PM +0100:
> > > Kees Cook <keescook@chromium.org>
> > >     net: dev: Convert sa_data to flexible array in struct sockaddr
> > > (ca13c2b1e9e4b5d982c2f1e75f28b1586e5c0f7f in this tree,
> > > b5f0de6df6dce8d641ef58ef7012f3304dffb9a1 upstream)
> > 
> > This commit breaks build of some 3rd party wireless module we use here
> > (because sizeof(sa->sa_data) no longer works and needs to use
> > sa_data_min)

Just FYI, it's possible that things using sizeof(sa->sa_data) were buggy
to begin with since the struct size isn't actually dictated by that size
(it's only the minimum possible size).

> > With that said I guess it really is a dependency on the arp_req_get
> > overflow, so probably necessary evil, and I don't think we explicitly
> > pretend to preserve APIs for 3rd party modules so this is probably
> > fine... The new warnings that poped up (and were reported in other
> > messages) a probably worth checking though.
> 
> We NEVER preserve in-kernel APIs for any out-of-tree code as obviously,
> we have no idea what out-of-tree code is actually using, so it would be
> impossible to do so.
> 
> Also, it's odd that a driver is hit by this as no in-kernel driver was,
> so perhaps it's using the wrong api to start with :)

The reason is that most drivers don't want this size (see above) and
all the in-tree code that did need adjustment got adjusted (visible in
the referenced patch). :) But that's the risk of an out-of-tree driver:
it doesn't get those fixes automatically.

Out of curiosity, which drivers broke and what's needed to get them into
upstream (or at least staging)?

-Kees

-- 
Kees Cook