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authorPete Zaitcev <zaitcev@redhat.com>2021-03-03 22:10:53 -0600
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2021-03-10 09:36:13 +0100
commit9de2c43acf37a17dc4c69ff78bb099b80fb74325 (patch)
tree9e55d3ddd92eb2fa373e76be8d76e1f15635c824 /drivers/usb
parent414c20df7d401bcf1cb6c13d2dd944fb53ae4acf (diff)
USB: usblp: fix a hang in poll() if disconnected
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>
Diffstat (limited to 'drivers/usb')
-rw-r--r--drivers/usb/class/usblp.c16
1 files changed, 12 insertions, 4 deletions
diff --git a/drivers/usb/class/usblp.c b/drivers/usb/class/usblp.c
index c9f6e9758288..f27b4aecff3d 100644
--- a/drivers/usb/class/usblp.c
+++ b/drivers/usb/class/usblp.c
@@ -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;
}