Received-SPF: pass (google.com: domain of linux-kernel+bounces-149351-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Precedence: bulk
MIME-Version: 1.0
References: <20240417230637.2592473-1-dtokazaki@google.com> <CAMRc=Mcbi8BQ-tHNs+BVjbm3aDSVY0zzOM4QfND3d2y8ryT62g@mail.gmail.com>
In-Reply-To: <CAMRc=Mcbi8BQ-tHNs+BVjbm3aDSVY0zzOM4QfND3d2y8ryT62g@mail.gmail.com>
From: Bartosz Golaszewski <brgl@bgdev.pl>
Date: Thu, 18 Apr 2024 02:23:38 +0200
Message-ID: <CAMRc=McRiv6vtU5LySrkbfdbCaqZ2tXbHnazo4iahRS-SKAXxg@mail.gmail.com>
Subject: Re: [PATCH v1] at24: fix memory corruption race condition
To: Daniel Okazaki <dtokazaki@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, kernel-team@android.com, 
	linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Thu, Apr 18, 2024 at 1:59=E2=80=AFAM Bartosz Golaszewski <brgl@bgdev.pl>=
 wrote:
>
> On Thu, Apr 18, 2024 at 1:07=E2=80=AFAM Daniel Okazaki <dtokazaki@google.=
com> wrote:
> >
> > If the eeprom is not accessible, an nvmem device will be registered, th=
e
> > read will fail, and the device will be torn down. If another driver
> > accesses the nvmem device after the teardown, it will reference
> > invalid memory.
> >
> > Move the failure point before registering the nvmem device.
> >
> > Signed-off-by: Daniel Okazaki <dtokazaki@google.com>
> > ---
> >  drivers/misc/eeprom/at24.c | 18 +++++++++---------
> >  1 file changed, 9 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
> > index 572333ead5fb..4bd4f32bcdab 100644
> > --- a/drivers/misc/eeprom/at24.c
> > +++ b/drivers/misc/eeprom/at24.c
> > @@ -758,15 +758,6 @@ static int at24_probe(struct i2c_client *client)
> >         }
> >         pm_runtime_enable(dev);
> >
> > -       at24->nvmem =3D devm_nvmem_register(dev, &nvmem_config);
> > -       if (IS_ERR(at24->nvmem)) {
> > -               pm_runtime_disable(dev);
> > -               if (!pm_runtime_status_suspended(dev))
> > -                       regulator_disable(at24->vcc_reg);
> > -               return dev_err_probe(dev, PTR_ERR(at24->nvmem),
> > -                                    "failed to register nvmem\n");
> > -       }
> > -
> >         /*
> >          * Perform a one-byte test read to verify that the chip is func=
tional,
> >          * unless powering on the device is to be avoided during probe =
(i.e.
> > @@ -782,6 +773,15 @@ static int at24_probe(struct i2c_client *client)
> >                 }
> >         }
> >
> > +       at24->nvmem =3D devm_nvmem_register(dev, &nvmem_config);
> > +       if (IS_ERR(at24->nvmem)) {
> > +               pm_runtime_disable(dev);
> > +               if (!pm_runtime_status_suspended(dev))
> > +                       regulator_disable(at24->vcc_reg);
> > +               return dev_err_probe(dev, PTR_ERR(at24->nvmem),
> > +                                    "failed to register nvmem\n");
> > +       }
> > +
> >         /* If this a SPD EEPROM, probe for DDR3 thermal sensor */
> >         if (cdata =3D=3D &at24_data_spd)
> >                 at24_probe_temp_sensor(client);
> > --
> > 2.44.0.683.g7961c838ac-goog
> >
>
> Looks good, can you add a Fixes tag?
>
> Thanks,
> Bartosz

Wait... While the patch is still correct - we shouldn't needlessly
create the nvmem device - why would anything crash? Looks like a
problem with nvmem then? How did you trigger this issue?

Bart