lkml.org 
[lkml]   [2019]   [Mar]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH v2] tpm: fix an invalid condition in tpm_common_poll
    From
    Date
    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

    \
     
     \ /
      Last update: 2019-03-20 15:31    [W:2.131 / U:0.312 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site