linux-kernel - Re: [PATCH] tracing: Fix potential double free in create_var

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Date:   Mon, 25 Apr 2022 09:59:22 -0500
From:   Tom Zanussi <tom.zanussi@...ux.intel.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>,
        Keita Suzuki <keitasuzuki.park@...ab.ics.keio.ac.jp>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: Fix potential double free in create_var_ref()

On Sat, 2022-04-23 at 00:13 +0900, Masami Hiramatsu wrote:
> Hi Keita,
> 
> On Fri, 22 Apr 2022 06:00:25 +0000
> Keita Suzuki <keitasuzuki.park@...ab.ics.keio.ac.jp> wrote:
> 
> > In create_var_ref(), init_var_ref() is called to initialize the
> > fields
> > of variable ref_field, which is allocated in the previous function
> > call
> > to create_hist_field(). Function init_var_ref() allocates the
> > corresponding fields such as ref_field->system, but frees these
> > fields
> > when the function encounters an error. The caller later calls
> > destroy_hist_field() to conduct error handling, which frees the
> > fields
> > and the variable itself. This results in double free of the fields
> > which
> > are already freed in the previous function.
> > 
> > Fix this by storing NULL to the corresponding fields when they are
> > freed
> > in init_var_ref().
> > 
> 
> Good catch! this looks good to me.
> 
> Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>


Looks fine to me too, thanks,

Reviewed-by: Tom Zanussi <zanussi@...nel.org>


> 
> 
> BTW, could you Cc the original code authoer and  if you fix a bug and
> add Fixes: tag? That will help the original author can check the bug
> and
> help stable kernel maintainers to pick the patch. :)
> 
> To find the original commit, you can use the 'git blame'.
> 
> $ git blame kernel/trace/trace_events_hist.c -L 2093,2100
> 067fe038e70f6 (Tom Zanussi 2018-01-15 20:51:56 -0600
> 2093)      return err;
> 067fe038e70f6 (Tom Zanussi 2018-01-15 20:51:56 -0600 2094)  free:
> 067fe038e70f6 (Tom Zanussi 2018-01-15 20:51:56 -0600
> 2095)      kfree(ref_field->system);
> 067fe038e70f6 (Tom Zanussi 2018-01-15 20:51:56 -0600
> 2096)      kfree(ref_field->event_name);
> 067fe038e70f6 (Tom Zanussi 2018-01-15 20:51:56 -0600
> 2097)      kfree(ref_field->name);
> 067fe038e70f6 (Tom Zanussi 2018-01-15 20:51:56 -0600 2098) 
> 067fe038e70f6 (Tom Zanussi 2018-01-15 20:51:56 -0600 2099)      goto
> out;
> 067fe038e70f6 (Tom Zanussi 2018-01-15 20:51:56 -0600 2100) }
> 
> Then, git show will tell you the original author.
> $ git show 067fe038e70f6
> 
> And get the format of the commit for Fixes tag.
> 
> $ git --no-pager show -s --abbrev-commit --abbrev=12 --
> pretty=format:"%h (\"%s\")%n" 067fe038e70f6
> 067fe038e70f ("tracing: Add variable reference handling to hist
> triggers")
> 
> Then you can add lines like:
> 
> Fixes: 067fe038e70f ("tracing: Add variable reference handling to
> hist triggers")
> Cc: stable@...r.kernel.org
> 
> Thank you,
> 
> > Signed-off-by: Keita Suzuki <keitasuzuki.park@...ab.ics.keio.ac.jp>
> > ---
> >  kernel/trace/trace_events_hist.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/kernel/trace/trace_events_hist.c
> > b/kernel/trace/trace_events_hist.c
> > index 44db5ba9cabb..a0e41906d9ce 100644
> > --- a/kernel/trace/trace_events_hist.c
> > +++ b/kernel/trace/trace_events_hist.c
> > @@ -2093,8 +2093,11 @@ static int init_var_ref(struct hist_field
> > *ref_field,
> >  	return err;
> >   free:
> >  	kfree(ref_field->system);
> > +	ref_field->system = NULL;
> >  	kfree(ref_field->event_name);
> > +	ref_field->event_name = NULL;
> >  	kfree(ref_field->name);
> > +	ref_field->name = NULL;
> >  
> >  	goto out;
> >  }
> > -- 
> > 2.25.1
> > 
> 
>