netdev - Re: [PATCH] net: xfrm: use preempt-safe this_cpu_read() in ipcomp_alloc

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Date:   Wed, 07 Mar 2018 12:21:21 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Greg Hackmann <ghackmann@...gle.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: xfrm: use preempt-safe this_cpu_read() in
 ipcomp_alloc_tfms()

On Wed, 2018-03-07 at 11:24 -0800, Greg Hackmann wrote:
> f7c83bcbfaf5 ("net: xfrm: use __this_cpu_read per-cpu helper") added
> a
> __this_cpu_read() call inside ipcomp_alloc_tfms().  Since this call
> was
> introduced, the rules around per-cpu accessors have been tightened
> and
> __this_cpu_read() cannot be used in a preemptible context.
> 
> syzkaller reported this leading to the following kernel BUG while
> fuzzing sendmsg:
> 
> 
> Cc: stable@...r.kernel.org

Hi Greg, thanks for this patch.

1) Please read Documentation/networking/netdev-FAQ.txt
around line 133

2) If you believe this needs to be backported, you must provide
a Fixes: tag to clearly identify commit that changed the behavior.

Otherwise dozens of stable teams will have to figure out by themselves,
wasting precious time.

Thanks.