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

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Message-ID: <Y4B17nBArWS1Iywo@hirez.programming.kicks-ass.net>
Date:   Fri, 25 Nov 2022 08:59:42 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dmitry Safonov <dima@...sta.com>
Cc:     linux-kernel@...r.kernel.org, David Ahern <dsahern@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Bob Gilligan <gilligan@...sta.com>,
        "David S. Miller" <davem@...emloft.net>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Francesco Ruggeri <fruggeri@...sta.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.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
Subject: Re: [PATCH v6 1/5] jump_label: Prevent key->enabled int overflow

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>

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.