[PATCH v2] tpm: fix an invalid condition in tpm_common_poll

[PATCH v2] tpm: fix an invalid condition in tpm_common_poll

[Tadeusz Struk]

The poll condition should only check response_length,
because reads should only be issued if there is data to read.
The response_read flag only prevents double writes.
The problem was that the write set the response_read to false,
enqued a tpm job, and returned. Then application called poll
which checked the response_read flag and returned EPOLLIN.
Then the application called read, but got nothing.
After all that the async_work kicked in.
Added also mutex_lock around the poll check to prevent
other possible race conditions.

Fixes: 9488585b21bef0df12 ("tpm: add support for partial reads")
Reported-by: Mantas Mikulėnas <grawity@gmail.com>
Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
---
 drivers/char/tpm/tpm-dev-common.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/char/tpm/tpm-dev-common.c b/drivers/char/tpm/tpm-dev-common.c
index 5eecad233ea1..7312d3214381 100644
--- a/drivers/char/tpm/tpm-dev-common.c
+++ b/drivers/char/tpm/tpm-dev-common.c
@@ -203,12 +203,14 @@ __poll_t tpm_common_poll(struct file *file, poll_table *wait)
 	__poll_t mask = 0;
 
 	poll_wait(file, &priv->async_wait, wait);
+	mutex_lock(&priv->buffer_mutex);
 
-	if (!priv->response_read || priv->response_length)
+	if (priv->response_length)
 		mask = EPOLLIN | EPOLLRDNORM;
 	else
 		mask = EPOLLOUT | EPOLLWRNORM;
 
+	mutex_unlock(&priv->buffer_mutex);
 	return mask;
 }
 

Re: [PATCH v2] tpm: fix an invalid condition in tpm_common_poll

[James Bottomley]

On Tue, 2019-03-19 at 13:31 -0700, Tadeusz Struk wrote:
> The poll condition should only check response_length,
> because reads should only be issued if there is data to read.
> The response_read flag only prevents double writes.
> The problem was that the write set the response_read to false,
> enqued a tpm job, and returned. Then application called poll
> which checked the response_read flag and returned EPOLLIN.
> Then the application called read, but got nothing.
> After all that the async_work kicked in.
> Added also mutex_lock around the poll check to prevent
> other possible race conditions.
> 
> Fixes: 9488585b21bef0df12 ("tpm: add support for partial reads")
> Reported-by: Mantas Mikulėnas <grawity@gmail.com>
> Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
> ---
>  drivers/char/tpm/tpm-dev-common.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm-dev-common.c
> b/drivers/char/tpm/tpm-dev-common.c
> index 5eecad233ea1..7312d3214381 100644
> --- a/drivers/char/tpm/tpm-dev-common.c
> +++ b/drivers/char/tpm/tpm-dev-common.c
> @@ -203,12 +203,14 @@ __poll_t tpm_common_poll(struct file *file,
> poll_table *wait)
>  	__poll_t mask = 0;
>  
>  	poll_wait(file, &priv->async_wait, wait);
> +	mutex_lock(&priv->buffer_mutex);
>  
> -	if (!priv->response_read || priv->response_length)
> +	if (priv->response_length)
>  		mask = EPOLLIN | EPOLLRDNORM;
>  	else
>  		mask = EPOLLOUT | EPOLLWRNORM;
>  
> +	mutex_unlock(&priv->buffer_mutex);

Just an observation on this: the mutex is now no-longer necessary
because a read on a size_t quantity is always atomic.

James

Re: [PATCH v2] tpm: fix an invalid condition in tpm_common_poll

[Tadeusz Struk]

On 3/20/19 7:30 AM, James Bottomley wrote:
> Just an observation on this: the mutex is now no-longer necessary
> because a read on a size_t quantity is always atomic.

True, that's why it wasn't there at the beginning, but
then things changed and I forgot to add it, so let's
put it there just in case.

Thanks,
-- 
Tadeusz

Re: [PATCH v2] tpm: fix an invalid condition in tpm_common_poll

[Mantas Mikulėnas]

On Tue, Mar 19, 2019 at 10:31 PM Tadeusz Struk <tadeusz.struk@intel.com> wrote:
>
> The poll condition should only check response_length,
> because reads should only be issued if there is data to read.
> The response_read flag only prevents double writes.
> The problem was that the write set the response_read to false,
> enqued a tpm job, and returned. Then application called poll
> which checked the response_read flag and returned EPOLLIN.
> Then the application called read, but got nothing.
> After all that the async_work kicked in.
> Added also mutex_lock around the poll check to prevent
> other possible race conditions.
>
> Fixes: 9488585b21bef0df12 ("tpm: add support for partial reads")
> Reported-by: Mantas Mikulėnas <grawity@gmail.com>
> Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
> ---
>  drivers/char/tpm/tpm-dev-common.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/char/tpm/tpm-dev-common.c b/drivers/char/tpm/tpm-dev-common.c
> index 5eecad233ea1..7312d3214381 100644
> --- a/drivers/char/tpm/tpm-dev-common.c
> +++ b/drivers/char/tpm/tpm-dev-common.c
> @@ -203,12 +203,14 @@ __poll_t tpm_common_poll(struct file *file, poll_table *wait)
>         __poll_t mask = 0;
>
>         poll_wait(file, &priv->async_wait, wait);
> +       mutex_lock(&priv->buffer_mutex);
>
> -       if (!priv->response_read || priv->response_length)
> +       if (priv->response_length)
>                 mask = EPOLLIN | EPOLLRDNORM;
>         else
>                 mask = EPOLLOUT | EPOLLWRNORM;
>
> +       mutex_unlock(&priv->buffer_mutex);
>         return mask;
>  }

Thanks, this patch seems to work, and I apologize for not responding
to test the patches earlier.

Any chance it'll be submitted for stable 5.0.x as well?

-- 
Mantas Mikulėnas

Re: [PATCH v2] tpm: fix an invalid condition in tpm_common_poll

[Tadeusz Struk]

On 3/20/19 11:51 AM, Mantas Mikulėnas wrote:
> Thanks, this patch seems to work, and I apologize for not responding
> to test the patches earlier.

Thanks for testing.

> 
> Any chance it'll be submitted for stable 5.0.x as well?

Yes, it's a regression. I included the "Fixes" tag so
it should be applied to all affected versions.
In this case it's 5.0 only.
Thanks,
-- 
Tadeusz

Re: [PATCH v2] tpm: fix an invalid condition in tpm_common_poll

[Jarkko Sakkinen]

On Tue, Mar 19, 2019 at 01:31:34PM -0700, Tadeusz Struk wrote:
> The poll condition should only check response_length,
> because reads should only be issued if there is data to read.
> The response_read flag only prevents double writes.
> The problem was that the write set the response_read to false,
> enqued a tpm job, and returned. Then application called poll
> which checked the response_read flag and returned EPOLLIN.
> Then the application called read, but got nothing.
> After all that the async_work kicked in.
> Added also mutex_lock around the poll check to prevent
> other possible race conditions.
> 
> Fixes: 9488585b21bef0df12 ("tpm: add support for partial reads")
> Reported-by: Mantas Mikulėnas <grawity@gmail.com>
> Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>

Can you send v3 with the comment and cc to stable? Then this
should be fine.

/Jarkko

Re: [PATCH v2] tpm: fix an invalid condition in tpm_common_poll

[Jarkko Sakkinen]

On Wed, Mar 20, 2019 at 12:18:42PM -0700, Tadeusz Struk wrote:
> On 3/20/19 11:51 AM, Mantas Mikulėnas wrote:
> > Thanks, this patch seems to work, and I apologize for not responding
> > to test the patches earlier.
> 
> Thanks for testing.
> 
> > 
> > Any chance it'll be submitted for stable 5.0.x as well?
> 
> Yes, it's a regression. I included the "Fixes" tag so
> it should be applied to all affected versions.
> In this case it's 5.0 only.
> Thanks,
> -- 
> Tadeusz

Add a tested-by for the next version.

/Jarkko