Messages in this thread | | | Date | Tue, 03 Apr 2012 15:51:56 +0200 | From | Daniel Lezcano <> | Subject | Re: [PATCH] cpuidle: Avoid possible NULL pointer dereference in __cpuidle_register_device() |
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On 04/03/2012 03:15 PM, Srivatsa S. Bhat wrote: > On 04/03/2012 05:38 PM, Daniel Lezcano wrote: > >> On 04/03/2012 01:51 PM, Srivatsa S. Bhat wrote: >>> On 04/03/2012 01:01 AM, Daniel Lezcano wrote: >>> >>>> On 04/02/2012 04:44 PM, Srivatsa S. Bhat wrote: >>>>> In __cpuidle_register_device(), "dev->cpu" is used before checking if >>>>> dev is >>>>> non-NULL. Fix it. >>>>> >>>>> Signed-off-by: Srivatsa S. Bhat<srivatsa.bhat@linux.vnet.ibm.com> >>>>> --- >>>> >>>> That should be fixed at the caller level. Usually, static function does >>>> not check the function parameters, it is up to the exported function to >>>> do that. It is supposed the static functions are called with valid >>>> parameters. >>>> >>> >>> >>> Ok, good point! I hadn't thought about that.. I just happened to notice >>> that in __cpuidle_register_device(), the dev == NULL check is performed >>> _after_ dereferencing it, which made the check useless. So I tried to >>> fix that within that function. But thanks for pointing out the >>> semantics.. >>> >>>> There are two callers for __cpuidle_register_device: >>>> * cpuidle_register_device >>>> * cpuidle_enable_device >>>> >>>> Both of them do not check 'dev' is a valid parameter. They should as >>>> they are exported and could be used by an external module. IMHO, BUG_ON >>>> could be used here if dev == NULL. >>>> >>> >>> >>> BUG_ON? That would crash the system.. which might be unnecessary.. >> >> Mmh, yes, I agree. never mind. >> >>> How about checking if dev == NULL in the 2 callers like you suggested >>> and returning -EINVAL if dev is indeed NULL? >>> (And of course no checks for dev == NULL in __cpuidle_register_device). >> >> Ok for me. >> > > > Great! Here is the updated patch: > > --- > > From: Srivatsa S. Bhat<srivatsa.bhat@linux.vnet.ibm.com> > Subject: [PATCH v2] cpuidle: Add checks to avoid NULL pointer dereference > > The existing check for dev == NULL in __cpuidle_register_device() is rendered > useless because dev is dereferenced before the check itself. Moreover, > correctly speaking, it is the job of the callers of this function, i.e., > cpuidle_register_device()& cpuidle_enable_device() (which also happen to be > exported functions) to ensure that __cpuidle_register_device() is called with > a non-NULL dev. > > So add the necessary dev == NULL checks in the two callers and remove the > (useless) check from __cpuidle_register_device(). > > Signed-off-by: Srivatsa S. Bhat<srivatsa.bhat@linux.vnet.ibm.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Thanks -- Daniel
ps : shouldn't this patch be sent in a separate email ?
> --- > > drivers/cpuidle/cpuidle.c | 8 ++++++-- > 1 files changed, 6 insertions(+), 2 deletions(-) > > diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c > index 87411ce..eae2f11 100644 > --- a/drivers/cpuidle/cpuidle.c > +++ b/drivers/cpuidle/cpuidle.c > @@ -291,6 +291,9 @@ int cpuidle_enable_device(struct cpuidle_device *dev) > int ret, i; > struct cpuidle_driver *drv = cpuidle_get_driver(); > > + if (!dev) > + return -EINVAL; > + > if (dev->enabled) > return 0; > if (!drv || !cpuidle_curr_governor) > @@ -375,8 +378,6 @@ static int __cpuidle_register_device(struct cpuidle_device *dev) > struct device *cpu_dev = get_cpu_device((unsigned long)dev->cpu); > struct cpuidle_driver *cpuidle_driver = cpuidle_get_driver(); > > - if (!dev) > - return -EINVAL; > if (!try_module_get(cpuidle_driver->owner)) > return -EINVAL; > > @@ -401,6 +402,9 @@ int cpuidle_register_device(struct cpuidle_device *dev) > { > int ret; > > + if (!dev) > + return -EINVAL; > + > mutex_lock(&cpuidle_lock); > > if ((ret = __cpuidle_register_device(dev))) { > >
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