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Sun, 05 Jan 2020 22:52:52 -0800 (PST) Date: Mon, 6 Jan 2020 14:52:49 +0800 From: chenqiwu To: Viresh Kumar Subject: Re: [PATCH] cpufreq: s3c: avoid use after free issue in xxx_cpufreq_reboot_notifier_evt() Message-ID: <20200106065249.GA16392@cqw-OptiPlex-7050> References: <1577515439-14477-1-git-send-email-qiwuchen55@gmail.com> <20200106054811.uduf2qdn5ecvbwrc@vireshk-i7> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200106054811.uduf2qdn5ecvbwrc@vireshk-i7> User-Agent: Mutt/1.5.21 (2010-09-15) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200105_225253_788293_7BF43C44 X-CRM114-Status: GOOD ( 22.80 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-samsung-soc@vger.kernel.org, linux-pm@vger.kernel.org, rjw@rjwysocki.net, krzk@kernel.org, kgene@kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Jan 06, 2020 at 11:18:11AM +0530, Viresh Kumar wrote: > On 28-12-19, 14:43, qiwuchen55@gmail.com wrote: > > From: chenqiwu > > > > There is a potential UAF issue in xxx_cpufreq_reboot_notifier_evt() that > > the cpufreq policy of cpu0 has been released before using it. So we should > > make a judgement to avoid it. > > There is no UAF problem here, but that we do cpufreq_cpu_get() with a > corresponding cpufreq_cpu_put(). > > > Signed-off-by: chenqiwu > > --- > > drivers/cpufreq/s3c2416-cpufreq.c | 11 ++++++++++- > > drivers/cpufreq/s5pv210-cpufreq.c | 10 +++++++++- > > 2 files changed, 19 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/cpufreq/s3c2416-cpufreq.c b/drivers/cpufreq/s3c2416-cpufreq.c > > index 1069103..0f576ba 100644 > > --- a/drivers/cpufreq/s3c2416-cpufreq.c > > +++ b/drivers/cpufreq/s3c2416-cpufreq.c > > @@ -304,6 +304,7 @@ static int s3c2416_cpufreq_reboot_notifier_evt(struct notifier_block *this, > > { > > struct s3c2416_data *s3c_freq = &s3c2416_cpufreq; > > int ret; > > + struct cpufreq_policy policy; > > > > mutex_lock(&cpufreq_lock); > > > > @@ -318,7 +319,15 @@ static int s3c2416_cpufreq_reboot_notifier_evt(struct notifier_block *this, > > */ > > if (s3c_freq->is_dvs) { > > pr_debug("cpufreq: leave dvs on reboot\n"); > > - ret = cpufreq_driver_target(cpufreq_cpu_get(0), FREQ_SLEEP, 0); > > + > > + memset(&policy, 0, sizeof(policy)); > > + ret = cpufreq_get_policy(&policy, 0); > > + if (ret < 0) { > > + pr_debug("cpufreq: get no policy for cpu0\n"); > > + return NOTIFY_BAD; > > + } > > + > > This doesn't make sense to me, why don't you do cpufreq_cpu_get() and > put() instead ? > Hi viresh, I can't explain which approach is better, but I think both approaches are effective for the situation. By the way, there is a possibility that the cpu0 hotplug thread will call cpufreq_policy_free() to free cpufreq policy if cpu0 hotplug failed. I think there should be a judgement to avoid this UAF risk if necessary, or we just do panic if cpu0's cpufreq policy is free. > > + ret = cpufreq_driver_target(&policy, FREQ_SLEEP, 0); > > if (ret < 0) > > return NOTIFY_BAD; > > } > > diff --git a/drivers/cpufreq/s5pv210-cpufreq.c b/drivers/cpufreq/s5pv210-cpufreq.c > > index 5d10030..d99b4b1 100644 > > --- a/drivers/cpufreq/s5pv210-cpufreq.c > > +++ b/drivers/cpufreq/s5pv210-cpufreq.c > > @@ -555,8 +555,16 @@ static int s5pv210_cpufreq_reboot_notifier_event(struct notifier_block *this, > > unsigned long event, void *ptr) > > { > > int ret; > > + struct cpufreq_policy *policy; > > > > - ret = cpufreq_driver_target(cpufreq_cpu_get(0), SLEEP_FREQ, 0); > > + policy = cpufreq_cpu_get(0); > > + if (!policy) { > > + pr_debug("cpufreq: get no policy for cpu0\n"); > > + return NOTIFY_BAD; > > + } > > + > > + ret = cpufreq_driver_target(policy, SLEEP_FREQ, 0); > > + cpufreq_cpu_put(policy); > > Like what is done here. > > Also add a blank line here. > > > if (ret < 0) > > return NOTIFY_BAD; > > > > -- > > 1.9.1 > > -- > viresh Thanks for your review! Qiwu _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel