linux-kernel - Re: [PATCH] perf ordered_events: fix crash in free_dup

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Date:   Tue, 7 Aug 2018 10:50:10 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Stephane Eranian <eranian@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, mingo@...e.hu
Subject: Re: [PATCH] perf ordered_events: fix crash in free_dup_event()

On Tue, Aug 07, 2018 at 01:16:22AM -0700, Stephane Eranian wrote:
> On Tue, Aug 7, 2018 at 12:20 AM Jiri Olsa <jolsa@...hat.com> wrote:
> >
> > On Mon, Aug 06, 2018 at 06:23:35PM -0700, Stephane Eranian wrote:
> > > Depending on memory allocations, it was possible to get a SEGFAULT in
> > > free_dup_event() because the event pointer was bogus:
> > >
> > > perf[1354]: segfault at ffffffff00000006 ip 00000000004b7fc7
> >
> > is there any reproducer?
> >
> The cmdline is simple:
> $ perf record -e cycles:pp -o - -a sleep 1 | perf inject -b -i - >/dev/null
> I was using v4.13 for my tests and it may be sensitive to compiler.
> Was using LLVM.

I can't make it fail even when I compile with clang 'make CC=clang'

  [jolsa@...va perf]$ clang --version
  clang version 6.0.1 (tags/RELEASE_601/final)

I'm on v4.17, but I dont think kernel version is related to this issue

> 
> It may be a compiler related issue. You do not allocate the whole struct.
> If the compiler was to do a memcpy() behind your back, you'd be in
> troubles.
> 
> Adding extra padding before *event was also avoiding the problem.
> struct ordered_event {
>         u64                     timestamp;
>         u64                     file_offset;
>         char                   pad[32];   <----- extra padding for debugging
>         union perf_event        *event;
>         struct list_head        list;
> };

might be some issue in the struct ordered_event allocation,
which is little convoluted 

jirka