Subject: Re: [PATCH] net: xfrm: use preempt-safe this_cpu_read() in ipcomp_alloc_tfms()

From: Eric Dumazet <[email-masked]>
Date: Wed, 07 Mar 2018 12:21:21 -0800

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: [email-masked]

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.