netdev - Re: [PATCH] [RFC] xfrm: work around a clang-19 fortifiy-string false-positive

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Message-Id: <f94c6943-eb93-4533-8e4d-3645ef38b990@app.fastmail.com>
Date: Tue, 09 Apr 2024 21:41:09 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Nathan Chancellor" <nathan@...nel.org>
Cc: "Kees Cook" <keescook@...omium.org>, "Arnd Bergmann" <arnd@...nel.org>,
 "Steffen Klassert" <steffen.klassert@...unet.com>,
 "Herbert Xu" <herbert@...dor.apana.org.au>,
 "David S . Miller" <davem@...emloft.net>,
 "Eric Dumazet" <edumazet@...gle.com>, "Jakub Kicinski" <kuba@...nel.org>,
 "Paolo Abeni" <pabeni@...hat.com>,
 "Nick Desaulniers" <ndesaulniers@...gle.com>,
 "Bill Wendling" <morbo@...gle.com>, "Justin Stitt" <justinstitt@...gle.com>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 "Leon Romanovsky" <leon@...nel.org>, "Lin Ma" <linma@....edu.cn>,
 "Simon Horman" <horms@...nel.org>, "Breno Leitao" <leitao@...ian.org>,
 "Tobias Brunner" <tobias@...ongswan.org>, "Raed Salem" <raeds@...dia.com>,
 Netdev <netdev@...r.kernel.org>, linux-kernel@...r.kernel.org,
 llvm@...ts.linux.dev
Subject: Re: [PATCH] [RFC] xfrm: work around a clang-19 fortifiy-string false-positive

On Tue, Apr 9, 2024, at 18:15, Nathan Chancellor wrote:
> On Mon, Apr 08, 2024 at 09:06:21AM +0200, Arnd Bergmann wrote:
>> >
>> > The shorter fix (in the issue) is to explicitly range-check before
>> > the loop:
>> >
>> >        if (xp->xfrm_nr > XFRM_MAX_DEPTH)
>> >                return -ENOBUFS;
>> 
>> I ran into this issue again and I see that Nathan's fix has
>> made it into mainline and backports, but it's apparently
>> not sufficient.
>> 
>> I don't see the warning with my patch from this thread, but
>> there may still be a better fix.
>
> Is it the exact same warning? clang-19 or older?
> What > architecture/configuration? If my change is not sufficient then maybe
> there are two separate issues here? I have not seen this warning appear
> in our CI since my change was applied.

I only see it with clang-19. I've never seen it with arm32 and
currently only see it with arm64, though I had seen it with x86-64
as well in February before your patch.

The warning is the same as before aside from the line number,
which which is now include/linux/fortify-string.h:462:4
where it was line 420, but I think that is just a context
change.

I have a number of configs that reproduce this bug, see
https://pastebin.com/tMgfD7cu for an example with current
linux-next.

     Arnd