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USB: usblp: fix a hang in poll() if disconnected 

commit 9de2c43acf37a17dc4c69ff78bb099b80fb74325 upstream.

Apparently an application that opens a device and calls select()
on it, will hang if the decice is disconnected. It's a little
surprising that we had this bug for 15 years, but apparently
nobody ever uses select() with a printer: only write() and read(),
and those work fine. Well, you can also select() with a timeout.

The fix is modeled after devio.c. A few other drivers check the
condition first, then do not add the wait queue in case the
device is disconnected. We doubt that's completely race-free.
So, this patch adds the process first, then locks properly
and checks for the disconnect.

Reviewed-by: Zqiang <qiang.zhang@windriver.com>
Signed-off-by: Pete Zaitcev <zaitcev@redhat.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210303221053.1cf3313e@suzdal.zaitcev.lan
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Pete Zaitcev 2021-03-03 22:10:53 -06:00 committed by Greg Kroah-Hartman
parent cc495be174
commit c9e3462346
1 changed files with 12 additions and 4 deletions
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16
drivers/usb/class/usblp.c
View File

@ -494,16 +494,24 @@ static int usblp_release(struct inode *inode, struct file *file)
/* No kernel lock - fine */
static __poll_t usblp_poll(struct file *file, struct poll_table_struct *wait)
{
__poll_t ret;
struct usblp *usblp = file->private_data;
__poll_t ret = 0;
unsigned long flags;
struct usblp *usblp = file->private_data;
/* Should we check file->f_mode & FMODE_WRITE before poll_wait()? */
poll_wait(file, &usblp->rwait, wait);
poll_wait(file, &usblp->wwait, wait);
mutex_lock(&usblp->mut);
if (!usblp->present)
ret |= EPOLLHUP;
mutex_unlock(&usblp->mut);
spin_lock_irqsave(&usblp->lock, flags);
ret = ((usblp->bidir && usblp->rcomplete) ? EPOLLIN | EPOLLRDNORM : 0) |
((usblp->no_paper || usblp->wcomplete) ? EPOLLOUT | EPOLLWRNORM : 0);
if (usblp->bidir && usblp->rcomplete)
ret |= EPOLLIN | EPOLLRDNORM;
if (usblp->no_paper || usblp->wcomplete)
ret |= EPOLLOUT | EPOLLWRNORM;
spin_unlock_irqrestore(&usblp->lock, flags);
return ret;
}