From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752770Ab1LTTja (ORCPT ); Tue, 20 Dec 2011 14:39:30 -0500 Received: from mail.tpi.com ([70.99.223.143]:2879 "EHLO mail.tpi.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751715Ab1LTTjX (ORCPT ); Tue, 20 Dec 2011 14:39:23 -0500 Message-ID: <4EF0E465.5060704@canonical.com> Date: Tue, 20 Dec 2011 12:39:17 -0700 From: Tim Gardner User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:9.0) Gecko/20111215 Thunderbird/9.0 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> In-Reply-To: <4EF0B9F8.9020305@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 12/20/2011 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 -- Tim Gardner tim.gardner@canonical.com