From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754481Ab1LVSoU (ORCPT ); Thu, 22 Dec 2011 13:44:20 -0500 Received: from mail.tpi.com ([70.99.223.143]:3265 "EHLO mail.tpi.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752186Ab1LVSoT (ORCPT ); Thu, 22 Dec 2011 13:44:19 -0500 Message-ID: <4EF37A7A.2060504@canonical.com> Date: Thu, 22 Dec 2011 11:44:10 -0700 From: Tim Gardner User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.23) Gecko/20110921 Thunderbird/3.1.15 MIME-Version: 1.0 To: Rajiv Andrade CC: linux-kernel@vger.kernel.org, Seth Forshee , Debora Velarde , Marcel Selhorst , tpmdd-devel@lists.sourceforge.net Subject: Re: [PATCH 2/3] TPM: Close data_pending and data_buffer races References: <1323196162-2717-1-git-send-email-tim.gardner@canonical.com> <1323196162-2717-3-git-send-email-tim.gardner@canonical.com> <4EF0B9F8.9020305@linux.vnet.ibm.com> <4EF0E465.5060704@canonical.com> <4EF36C1F.6040409@linux.vnet.ibm.com> In-Reply-To: <4EF36C1F.6040409@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/22/2011 10:42 AM, Rajiv Andrade wrote: > On 20-12-2011 17:39, Tim Gardner wrote: >> On 12/20/2011 09:38 AM, Rajiv Andrade wrote: >>> On 06/12/11 16:29, Tim Gardner wrote: >>>> There is a race betwen tpm_read() and tpm_write where both >>>> chip->data_pending >>>> and chip->data_buffer can be changed by tpm_write() when tpm_read() >>>> clears chip->data_pending, but before tpm_read() grabs the mutex. >>>> >>>> Protect changes to chip->data_pending and chip->data_buffer by >>>> expanding >>>> the scope of chip->buffer_mutex. >>>> >>>> Reported-by: Seth Forshee >>>> Cc: Debora Velarde >>>> Cc: Rajiv Andrade >>>> Cc: Marcel Selhorst >>>> Cc: tpmdd-devel@lists.sourceforge.net >>>> Cc: stable@vger.kernel.org >>>> Signed-off-by: Tim Gardner >>>> --- >>>> drivers/char/tpm/tpm.c | 17 +++++++++-------- >>>> 1 files changed, 9 insertions(+), 8 deletions(-) >>>> >>>> diff --git a/drivers/char/tpm/tpm.c b/drivers/char/tpm/tpm.c >>>> index b366b34..70bf9e5 100644 >>>> --- a/drivers/char/tpm/tpm.c >>>> +++ b/drivers/char/tpm/tpm.c >>>> @@ -1074,12 +1074,15 @@ ssize_t tpm_write(struct file *file, const >>>> char __user *buf, >>>> struct tpm_chip *chip = file->private_data; >>>> size_t in_size = size, out_size; >>>> >>>> + mutex_lock(&chip->buffer_mutex); >>>> + >>>> /* cannot perform a write until the read has cleared >>>> either via tpm_read or a user_read_timer timeout */ >>>> - while (atomic_read(&chip->data_pending) != 0) >>>> + while (atomic_read(&chip->data_pending) != 0) { >>>> + mutex_unlock(&chip->buffer_mutex); >>>> msleep(TPM_TIMEOUT); >>>> - >>>> - mutex_lock(&chip->buffer_mutex); >>>> + mutex_lock(&chip->buffer_mutex); >>>> + } >>>> >>>> if (in_size> TPM_BUFSIZE) >>>> in_size = TPM_BUFSIZE; >>>> @@ -1112,22 +1115,20 @@ ssize_t tpm_read(struct file *file, char >>>> __user *buf, >>>> >>>> del_singleshot_timer_sync(&chip->user_read_timer); >>>> flush_work_sync(&chip->work); >>>> - ret_size = atomic_read(&chip->data_pending); >>>> - atomic_set(&chip->data_pending, 0); >>>> + mutex_lock(&chip->buffer_mutex); >>>> + ret_size = atomic_xchg(&chip->data_pending, 0); >>>> if (ret_size> 0) { /* relay data */ >>>> ssize_t orig_ret_size = ret_size; >>>> if (size< ret_size) >>>> ret_size = size; >>>> >>>> - mutex_lock(&chip->buffer_mutex); >>>> rc = copy_to_user(buf, chip->data_buffer, ret_size); >>>> memset(chip->data_buffer, 0, orig_ret_size); >>>> if (rc) >>>> ret_size = -EFAULT; >>> >>> What about just moving atomic_set(&chip->data_pending, 0); to here? >>> If I'm not missing anything, this would be cleaner. >>> >>> Rajiv >> >> I'm not sure I agree. Moving just that statement doesn't close the >> race. Perhaps you could send me your version of this patch so that its >> clear what you are suggesting. >> >> rtg > diff --git a/drivers/char/tpm/tpm.c b/drivers/char/tpm/tpm.c > index 6a8771f..6a37212b 100644 > --- a/drivers/char/tpm/tpm.c > +++ b/drivers/char/tpm/tpm.c > @@ -1210,7 +1210,6 @@ ssize_t tpm_read(struct file *file, char __user *buf, > del_singleshot_timer_sync(&chip->user_read_timer); > flush_work_sync(&chip->work); > ret_size = atomic_read(&chip->data_pending); > - atomic_set(&chip->data_pending, 0); > if (ret_size> 0) { /* relay data */ > if (size< ret_size) > ret_size = size; > @@ -1223,6 +1222,7 @@ ssize_t tpm_read(struct file *file, char __user *buf, > mutex_unlock(&chip->buffer_mutex); > } + atomic_set(&chip->data_pending, 0); > return ret_size; > } > > If we reset chip->data_pending after the buffer was copied to userspace, > it's guaranteed that tpm_write() won't touch such buffer before tpm_read() > handles it, given it polls chip->data_pending first. > NAK - this patch makes it worse (if I'm reading your email client garbled patch correctly). Now it races with tpm_write() as well as timeout_work(). You cannot futz with chip->data_pending outside of the exclusion zones. Consider what will happen if a user process just loops doing reads. chip->data_pending gets cleared every time tpm_read() is called, regardless of what tpm_write() or timeout_work() are doing at the time. tpm_read() / tpm_write() is a simple producer consumer model. Just use mutexes in an uncomplicated way. There is no need for data_pending to be atomic_t. rtg -- Tim Gardner tim.gardner@canonical.com