Re: Re: [PATCH] lib/test_kmod: Fix a use after free in register_test_dev_kmod

[Luis Chamberlain]

On Thu, Mar 11, 2021 at 09:31:55PM +0800, lyl2019@xxxxxxxxxxxxxxxx wrote:
> 
> 
> 
> > -----原始邮件-----
> > 发件人: "Luis Chamberlain" <mcgrof@xxxxxxxxxx>
> > 发送时间: 2021-03-11 21:01:08 (星期四)
> > 收件人: "Lv Yunlong" <lyl2019@xxxxxxxxxxxxxxxx>
> > 抄送: linux-kernel@xxxxxxxxxxxxxxx
> > 主题: Re: [PATCH] lib/test_kmod: Fix a use after free in register_test_dev_kmod
> > 
> > On Thu, Mar 11, 2021 at 12:02:46AM -0800, Lv Yunlong wrote:
> > > In register_test_dev_kmod, it calls free_test_dev_kmod() to free
> > > test_dev. But free_test_dev_kmod() can't set the original pointer
> > > test_dev to NULL, because the test_dev was passed by it's value
> > > not reference.
> > 
> > Did you actually get a crash or something? If so can you supply the
> > actual log? If this is just an observation and you think this is an
> > issue, specifying that would help during patch review.
> > 
> >   Luis
> > 
> > > Signed-off-by: Lv Yunlong <lyl2019@xxxxxxxxxxxxxxxx>
> > > ---
> > >  lib/test_kmod.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/lib/test_kmod.c b/lib/test_kmod.c
> > > index 38c250fbace3..aa8a2a563d7e 100644
> > > --- a/lib/test_kmod.c
> > > +++ b/lib/test_kmod.c
> > > @@ -1124,7 +1124,6 @@ static void free_test_dev_kmod(struct kmod_test_device *test_dev)
> > >  		free_test_dev_info(test_dev);
> > >  		kmod_config_free(test_dev);
> > >  		vfree(test_dev);
> > > -		test_dev = NULL;
> > >  	}
> > >  }
> > >  
> > > @@ -1149,6 +1148,7 @@ static struct kmod_test_device *register_test_dev_kmod(void)
> > >  	if (ret) {
> > >  		pr_err("could not register misc device: %d\n", ret);
> > >  		free_test_dev_kmod(test_dev);
> > > +		test_dev = NULL;
> > >  		goto out;
> > >  	}
> > >  
> > > -- 
> > > 2.25.1
> > > 
> > > 
> 
> This problem was reported by source code analyzers developed by our Security Lab(Loccs).

This should be included in the commit log, please.

> We have confirmed this issue before submiting the patch.

How was this confirmed exactly.

  Luis