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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id t10sm574075pgp.15.2020.09.23.12.04.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Sep 2020 12:04:59 -0700 (PDT) Date: Wed, 23 Sep 2020 12:04:58 -0700 From: Kees Cook To: Greg KH Cc: Shuah Khan , arve@android.com, tkjos@android.com, maco@android.com, joel@joelfernandes.org, christian@brauner.io, hridya@google.com, surenb@google.com, devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 07/11] drivers/android/binder: convert stats, transaction_log to counter_atomic Message-ID: <202009231204.5531FBA23F@keescook> References: <4fe28fc5f315657e4af276b8a3c71d80a5eaa379.1600816121.git.skhan@linuxfoundation.org> <20200923051027.GA2578443@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200923051027.GA2578443@kroah.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 23, 2020 at 07:10:27AM +0200, Greg KH wrote: > On Tue, Sep 22, 2020 at 07:43:36PM -0600, Shuah Khan wrote: > > counter_atomic is introduced to be used when a variable is used as > > a simple counter and doesn't guard object lifetimes. This clearly > > differentiates atomic_t usages that guard object lifetimes. > > > > counter_atomic variables will wrap around to 0 when it overflows and > > should not be used to guard resource lifetimes, device usage and > > open counts that control state changes, and pm states. > > > > stats tracks per-process binder statistics. Unsure if there is a chance > > of this overflowing, other than stats getting reset to 0. Convert it to > > use counter_atomic. > > > > binder_transaction_log:cur is used to keep track of the current log entry > > location. Overflow is handled in the code. Since it is used as a > > counter, convert it to use counter_atomic. > > > > This conversion doesn't change the oveflow wrap around behavior. > > > > Signed-off-by: Shuah Khan > > --- > > drivers/android/binder.c | 41 ++++++++++++++++--------------- > > drivers/android/binder_internal.h | 3 ++- > > 2 files changed, 23 insertions(+), 21 deletions(-) > > > > diff --git a/drivers/android/binder.c b/drivers/android/binder.c > > index f936530a19b0..11a0407c46df 100644 > > --- a/drivers/android/binder.c > > +++ b/drivers/android/binder.c > > @@ -66,6 +66,7 @@ > > #include > > #include > > #include > > +#include > > > > #include > > #include > > @@ -172,22 +173,22 @@ enum binder_stat_types { > > }; > > > > struct binder_stats { > > - atomic_t br[_IOC_NR(BR_FAILED_REPLY) + 1]; > > - atomic_t bc[_IOC_NR(BC_REPLY_SG) + 1]; > > - atomic_t obj_created[BINDER_STAT_COUNT]; > > - atomic_t obj_deleted[BINDER_STAT_COUNT]; > > + struct counter_atomic br[_IOC_NR(BR_FAILED_REPLY) + 1]; > > + struct counter_atomic bc[_IOC_NR(BC_REPLY_SG) + 1]; > > + struct counter_atomic obj_created[BINDER_STAT_COUNT]; > > + struct counter_atomic obj_deleted[BINDER_STAT_COUNT]; > > These are just debugging statistics, no reason they have to be atomic > variables at all and they should be able to just be "struct counter" > variables instead. But there's no reason for them _not_ to be atomic. Please let's keep this API as always safe. Why even provide a new foot-gun here? -- Kees Cook