Re: use-after-free in sctp_do_sm

From	Jason Baron <jbaron@akamai.com>
Newsgroups	linux.kernel
Subject	Re: use-after-free in sctp_do_sm
Date	2015-12-04 18:20 +0100
Message-ID	<qC2bx-5CT-43@gated-at.bofh.it> (permalink)
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On 12/04/2015 12:03 PM, Joe Perches wrote:
> On Fri, 2015-12-04 at 11:47 -0500, Jason Baron wrote:
>> When DYNAMIC_DEBUG is enabled we have this wrapper from
>> include/linux/dynamic_debug.h:
>>
>> if (unlikely(descriptor.flags & _DPRINTK_FLAGS_PRINT))
>> 	<do debug stuff>
>>
>> So the compiler is not emitting the side-effects in this
>> case.
> 
> Huh?  Do I misunderstand what you are writing?

Yes, I wasn't terribly clear - I was trying to say that the
'side-effects', in this case the debug code and use-after-free, are
hidden behind the branch. They aren't invoked unless we enable the debug
statement.

Thanks,

-Jason

> 
> You are testing a variable that is not generally set
> so the call is not being performed in the general case,
> but the compiler can not elide the code.
> 
> If the variable was enabled via the control file, the
> __dynamic_pr_debug would be performed with the
> use-after-free.
> 
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Re: use-after-free in sctp_do_sm Joe Perches <joe@perches.com> - 2015-12-03 22:00 +0100
  Re: use-after-free in sctp_do_sm Dmitry Vyukov <dvyukov@google.com> - 2015-12-04 11:50 +0100
    Re: use-after-free in sctp_do_sm Marcelo Ricardo Leitner <marcelo.leitner@gmail.com> - 2015-12-04 14:00 +0100
      Re: use-after-free in sctp_do_sm Vlad Yasevich <vyasevich@gmail.com> - 2015-12-04 16:40 +0100
        Re: use-after-free in sctp_do_sm Aaron Conole <aconole@redhat.com> - 2015-12-04 17:00 +0100
  Re: use-after-free in sctp_do_sm Dmitry Vyukov <dvyukov@google.com> - 2015-12-04 17:20 +0100
    Re: use-after-free in sctp_do_sm Jason Baron <jbaron@akamai.com> - 2015-12-04 17:50 +0100
      Re: use-after-free in sctp_do_sm Joe Perches <joe@perches.com> - 2015-12-04 18:10 +0100
        Re: use-after-free in sctp_do_sm Jason Baron <jbaron@akamai.com> - 2015-12-04 18:20 +0100

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