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

[Herbert Xu]

On Thu, Mar 08, 2018 at 08:31:47AM -0800, Eric Dumazet wrote:
>
> Because that would not be nice.
> 
> this_cpu_read() is faster than going through raw_smp_processor_id() and
> per_cpu_ptr()

I see.  In that case I have no objections to this patch.

Thanks,
-- 
Email: Herbert Xu 
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

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

[Eric Dumazet]

On 03/07/2018 11:33 PM, Herbert Xu wrote:

On Wed, Mar 07, 2018 at 11:24:16AM -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:


How about reverting f7c83bcbfaf5 instead?

Thanks,



Because that would not be nice.

this_cpu_read() is faster than going through raw_smp_processor_id() and 
per_cpu_ptr()

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

[Herbert Xu]

On Wed, Mar 07, 2018 at 11:24:16AM -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:

How about reverting f7c83bcbfaf5 instead?

Thanks,
-- 
Email: Herbert Xu 
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

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

[Greg Hackmann]

On 03/07/2018 12:21 PM, Eric Dumazet wrote:
> 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: sta...@vger.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.
> 

Apologies, I forgot that netdev has its own stable rules.  I'll
double-check which kernels are impacted and resend with an updated
commit log.

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

[Eric Dumazet]

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: sta...@vger.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.