linux-kernel - Re: [PATCH v2 2/7] nvmem: fix another memory leak in error path

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Message-ID: <CAMRc=McQ4ESq4g82QGjZiM0+NWUBrjUv71Be7UXzZpSsa9xAig@mail.gmail.com>
Date:   Tue, 18 Feb 2020 11:05:44 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Khouloud Touil <ktouil@...libre.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH v2 2/7] nvmem: fix another memory leak in error path

wt., 18 lut 2020 o 10:56 Srinivas Kandagatla
<srinivas.kandagatla@...aro.org> napisał(a):
>
>
>
> On 18/02/2020 09:42, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> >
> > The nvmem struct is only freed on the first error check after its
> > allocation and leaked after that. Fix it with a new label.
> >
> > Cc: <stable@...r.kernel.org>
> > Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
> > ---
> >   drivers/nvmem/core.c | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> > index b0be03d5f240..c9b3f4047154 100644
> > --- a/drivers/nvmem/core.c
> > +++ b/drivers/nvmem/core.c
> > @@ -343,10 +343,8 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> >               return ERR_PTR(-ENOMEM);
> >
> >       rval  = ida_simple_get(&nvmem_ida, 0, 0, GFP_KERNEL);
> > -     if (rval < 0) {
> > -             kfree(nvmem);
> > -             return ERR_PTR(rval);
> > -     }
> > +     if (rval < 0)
> > +             goto err_free_nvmem;
> >       if (config->wp_gpio)
> >               nvmem->wp_gpio = config->wp_gpio;
> >       else
> > @@ -432,6 +430,8 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> >       put_device(&nvmem->dev);
> >   err_ida_remove:
> >       ida_simple_remove(&nvmem_ida, nvmem->id);
> > +err_free_nvmem:
> > +     kfree(nvmem);
>
> This is not correct fix to start with, if the device has already been
> intialized before jumping here then nvmem would be freed as part of
> nvmem_release().
>
> So the bug was actually introduced by adding err_ida_remove label.
>
> You can free nvmem at that point but not at any point after that as
> device core would be holding a reference to it.
>

OK I see - I missed the release() callback assignment. Frankly: I find
this split of resource management responsibility confusing. Since the
users are expected to call nvmem_unregister() anyway - wouldn't it be
more clear to just free all resources there? What is the advantage of
defining the release() callback for device type here?

Bartosz