Re: [PATCH][V2][next] rtc: ds1307: check for failed memory allocation on wdt

Alexandre Belloni
2020-04-02T14:53:20Z

On 02/04/2020 07:44:44-0700, Guenter Roeck wrote:
> On 4/2/20 6:52 AM, Colin King wrote:
> > From: Colin Ian King <colin.king@canonical.com>
> >
> > Currently a failed memory allocation will lead to a null pointer
> > dereference on point wdt. Fix this by checking for a failed allocation
> > and adding error return handling to function ds1307_wdt_register.
> > Also move the error exit label "exit" to allow a return statement to
> > be removed.
> >
> > Addresses-Coverity: ("Dereference null return")
> > Fixes: fd90d48db037 ("rtc: ds1307: add support for watchdog timer on ds1388")
> > Signed-off-by: Colin Ian King <colin.king@canonical.com>
> > ---
> > V2: move error exit label and remove a return statement, thanks to
> > Walter Harms for spotting this clean up.
> > ---
> > drivers/rtc/rtc-ds1307.c | 16 +++++++++-------
> > 1 file changed, 9 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
> > index fad042118862..c058b02efb4d 100644
> > --- a/drivers/rtc/rtc-ds1307.c
> > +++ b/drivers/rtc/rtc-ds1307.c
> > @@ -1665,14 +1665,16 @@ static const struct watchdog_ops ds1388_wdt_ops = {
> >
> > };
> >
> > -static void ds1307_wdt_register(struct ds1307 *ds1307)
> > +static int ds1307_wdt_register(struct ds1307 *ds1307)
> > {
> > struct watchdog_device *wdt;
> >
> > if (ds1307->type != ds_1388)
> > - return;
> > + return 0;
> >
> > wdt = devm_kzalloc(ds1307->dev, sizeof(*wdt), GFP_KERNEL);
> > + if (!wdt)
> > + return -ENOMEM;
> >
> > wdt->info = &ds1388_wdt_info;
> > wdt->ops = &ds1388_wdt_ops;
> > @@ -1683,10 +1685,13 @@ static void ds1307_wdt_register(struct ds1307 *ds1307)
> > watchdog_init_timeout(wdt, 0, ds1307->dev);
> > watchdog_set_drvdata(wdt, ds1307);
> > devm_watchdog_register_device(ds1307->dev, wdt);
> > +
> > + return 0;
> > }
> > #else
> > -static void ds1307_wdt_register(struct ds1307 *ds1307)
> > +static int ds1307_wdt_register(struct ds1307 *ds1307)
> > {
> > + return 0;
> > }
> > #endif /* CONFIG_WATCHDOG_CORE */
> >
> > @@ -1979,10 +1984,7 @@ static int ds1307_probe(struct i2c_client *client,
> >
> > ds1307_hwmon_register(ds1307);
> > ds1307_clks_register(ds1307);
> > - ds1307_wdt_register(ds1307);
> > -
> > - return 0;
> > -
> > + err = ds1307_wdt_register(ds1307);
>
> Ah, sorry, missed this one. The original idea was to ignore errors on purpose.
> Same as with hwmon. If you want to change this, fine with me. Note though
> that rtc_nvmem_register() now leaks a sysfs file if I understand the code
> correctly.

rtc_nvmem_unregister(rtc) should be called properly by
devm_rtc_release_device when the rtc_device is destroyed so I don't
think it leaks.

As stated, I also prefer keeping the watchdog optional and ignore the
error.

--
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering