linux-kernel - RE: [PATCH 0/9] tools subsystem refcounter conversions

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Date:   Thu, 23 Feb 2017 11:39:10 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "matija.glavinic-pecotic.ext@...ia.com" 
        <matija.glavinic-pecotic.ext@...ia.com>
Subject: RE: [PATCH 0/9] tools subsystem refcounter conversions

> Em Wed, Feb 22, 2017 at 08:23:29PM -0300, Arnaldo Carvalho de Melo
> escreveu:
> > Em Tue, Feb 21, 2017 at 12:39:35PM -0300, Arnaldo Carvalho de Melo
> escreveu:
> > > Em Tue, Feb 21, 2017 at 05:34:54PM +0200, Elena Reshetova escreveu:
> > > > Now when new refcount_t type and API are finally merged
> > > > (see include/linux/refcount.h), the following
> > > > patches convert various refcounters in the tools susystem from atomic_t
> > > > to refcount_t. By doing this we prevent intentional or accidental
> > > > underflows or overflows that can led to use-after-free vulnerabilities.
> > >
> > > Thanks for working on this! I was almost going to jump on doing this
> > > myself!
> > >
> > > I'll try and get this merged ASAP.
> >
> > So, please take a look at my tmp.perf/refcount branch at:
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git

I took a look on it and it looks good. Just one thing I want to double check with regards to this commit:
https://kernel.googlesource.com/pub/scm/linux/kernel/git/acme/linux/+/58d561002587bf2572f9e6f4d222659e4068fadf%5E%21/#F0

And more specifically to this chunk:

@@ -937,7 +937,7 @@
 		munmap(map->base, perf_mmap__mmap_len(map));
 		map->base = NULL;
 		map->fd = -1;
-		atomic_set(&map->refcnt, 0);
+		refcount_set(&map->refcnt, 0);
 	}
 	auxtrace_mmap__munmap(&map->auxtrace_mmap);
 }

So, when the refcount set to zero in this place, what exactly happens to the perf_map object after? 
I just want to double check that we don't have  another hiding reusage case here when refcounter later on is simply incremented vs. set to "2." 


> >
> > There are multiple fixes in it to get it to build and test it, so far,
> > with:
> >
> >   perf top -F 15000 -d 0
> >
> > while doing kernel builds and tight usleep 1 loops to create lots of
> > short lived threads with its map_groups, maps, dsos, etc.
> >
> > Now running some build tests in some 36 containers with assorted distros
> > and cross compilers.
> 
> Tomorrow I'll inject some refcount errors to test this all.


Thank you!

Best Regards,
Elena.