linux-kernel - Re: [PATCH v6 1/5] jump_label: Prevent key->enabled int overflow

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Message-ID: <2081d2ac-b2b5-9299-7239-dc4348ec0d0a@arista.com>
Date:   Fri, 25 Nov 2022 14:28:30 +0000
From:   Dmitry Safonov <dima@...sta.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Bob Gilligan <gilligan@...sta.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Francesco Ruggeri <fruggeri@...sta.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jason Baron <jbaron@...mai.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Salam Noureddine <noureddine@...sta.com>,
        Steven Rostedt <rostedt@...dmis.org>, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        David Ahern <dsahern@...nel.org>
Subject: Re: [PATCH v6 1/5] jump_label: Prevent key->enabled int overflow

On 11/25/22 07:59, Peter Zijlstra wrote:
> On Wed, Nov 23, 2022 at 05:38:55PM +0000, Dmitry Safonov wrote:
>> 1. With CONFIG_JUMP_LABEL=n static_key_slow_inc() doesn't have any
>>    protection against key->enabled refcounter overflow.
>> 2. With CONFIG_JUMP_LABEL=y static_key_slow_inc_cpuslocked()
>>    still may turn the refcounter negative as (v + 1) may overflow.
>>
>> key->enabled is indeed a ref-counter as it's documented in multiple
>> places: top comment in jump_label.h, Documentation/staging/static-keys.rst,
>> etc.
>>
>> As -1 is reserved for static key that's in process of being enabled,
>> functions would break with negative key->enabled refcount:
>> - for CONFIG_JUMP_LABEL=n negative return of static_key_count()
>>   breaks static_key_false(), static_key_true()
>> - the ref counter may become 0 from negative side by too many
>>   static_key_slow_inc() calls and lead to use-after-free issues.
>>
>> These flaws result in that some users have to introduce an additional
>> mutex and prevent the reference counter from overflowing themselves,
>> see bpf_enable_runtime_stats() checking the counter against INT_MAX / 2.
>>
>> Prevent the reference counter overflow by checking if (v + 1) > 0.
>> Change functions API to return whether the increment was successful.
>>
>> Signed-off-by: Dmitry Safonov <dima@...sta.com>
>> Acked-by: Jakub Kicinski <kuba@...nel.org>
> 
> This looks good to me:
> 
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Thank you, Peter!

> What is the plan for merging this? I'm assuming it would want to go
> through the network tree, but as already noted earlier it depends on a
> patch I have in tip/locking/core.
> 
> Now I checked, tip/locking/core is *just* that one patch, so it might be
> possible to merge that branch and this series into the network tree and
> note that during the pull request to Linus.

I initially thought it has to go through tip trees because of the
dependence, but as you say it's just one patch.

I was also asked by Jakub on v4 to wait for Eric's Ack/Review, so once I
get a go from him, I will send all 6 patches for inclusion into -net
tree, if that will be in time before the merge window.

Thanks again for the review and ack,
          Dmitry