Re: [PATCH] usb: use mutex_lock in iowarrior_read()

Jeongjun Park
2024-09-16T12:44:40Z

Oliver Neukum <oneukum@suse.com> wrote:
>
>
>
> On 16.09.24 06:15, Greg KH wrote:
> > On Mon, Sep 16, 2024 at 01:06:29PM +0900, Jeongjun Park wrote:
> >> Currently, iowarrior_read() does not provide any protection for the
> >> iowarrior structure, so the iowarrior structure is vulnerable to data-race.
> >>
> >> Therefore, I think it is appropriate to protect the structure using
> >> mutex_lock in iowarrior_read().
> >>
> >> Fixes: 946b960d13c1 ("USB: add driver for iowarrior devices.")
> >> Signed-off-by: Jeongjun Park <aha310510@gmail.com>
> >> ---
> >> drivers/usb/misc/iowarrior.c | 42 +++++++++++++++++++++++++++---------
> >> 1 file changed, 32 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/drivers/usb/misc/iowarrior.c b/drivers/usb/misc/iowarrior.c
> >> index 6d28467ce352..7f3d37b395c3 100644
> >> --- a/drivers/usb/misc/iowarrior.c
> >> +++ b/drivers/usb/misc/iowarrior.c
> >> @@ -277,28 +277,41 @@ static ssize_t iowarrior_read(struct file *file, char __user *buffer,
> >> struct iowarrior *dev;
> >> int read_idx;
> >> int offset;
> >> + int retval = 0;
> >>
> >> dev = file->private_data;
> >>
> >> + if (!dev) {
> >
> > How can this happen? How was this tested?
>
> It cannot happen.
>
> [..]
> >> + mutex_lock(&dev->mutex);
> >
> > Please use the guard() form here, it makes the change much simpler and
> > easier to review and maintain.
>
> That would break the O_NONBLOCK case.
>
> Looking at the code it indeed looks like iowarrior_read() can race
> with itself. Strictly speaking it always could happen if a task used
> fork() after open(). The driver tries to restrict its usage to one
> thread, but I doubt that the logic is functional.
>
> It seems to me the correct fix is something like this:

Well, I don't know why it's necessary to modify it like this.
I think it would be more appropriate to patch it to make it
more maintainable by using guard() as Greg suggested.

>
> From 1627bc3a8e9aae60bdfc85430db2a44283e71a68 Mon Sep 17 00:00:00 2001
> From: Oliver Neukum <oneukum@suse.com>
> Date: Thu, 12 Sep 2024 12:47:33 +0200
> Subject: [PATCH] iowarrior: fix read racing against itself case
>
> In a multithreaded application iowarrior_read() can race against itself.
> It needs to take the mutex.
>
> Signed-off-by: Oliver Neukum <oneukum@suse.com>
> ---
> drivers/usb/misc/iowarrior.c | 33 ++++++++++++++++++++++++++-------
> 1 file changed, 26 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/usb/misc/iowarrior.c b/drivers/usb/misc/iowarrior.c
> index 6d28467ce352..3b49d6c7b569 100644
> --- a/drivers/usb/misc/iowarrior.c
> +++ b/drivers/usb/misc/iowarrior.c
> @@ -277,6 +277,8 @@ static ssize_t iowarrior_read(struct file *file, char __user *buffer,
> struct iowarrior *dev;
> int read_idx;
> int offset;
> + int result;
> + bool nonblock = file->f_flags & O_NONBLOCK;
>
> dev = file->private_data;
>
> @@ -292,14 +294,25 @@ static ssize_t iowarrior_read(struct file *file, char __user *buffer,
> && (count != (dev->report_size + 1)))
> return -EINVAL;
>
> + if (nonblock) {
> + result = mutex_trylock(&dev->mutex);
> + if (!result)
> + return -EAGAIN;
> + result = 0;
> + } else {
> + result = mutex_lock_interruptible(&dev->mutex);
> + if (result < 0)
> + return -EINTR;
> + }
> /* repeat until no buffer overrun in callback handler occur */
> do {
> atomic_set(&dev->overflow_flag, 0);
> if ((read_idx = read_index(dev)) == -1) {
> /* queue empty */
> - if (file->f_flags & O_NONBLOCK)
> - return -EAGAIN;
> - else {
> + if (nonblock) {
> + result = -EAGAIN;
> + goto out;
> + } else {
> //next line will return when there is either new data, or the device is unplugged
> int r = wait_event_interruptible(dev->read_wait,
> (!dev->present
> @@ -309,14 +322,17 @@ static ssize_t iowarrior_read(struct file *file, char __user *buffer,
> -1));
> if (r) {
> //we were interrupted by a signal
> - return -ERESTART;
> + result = -ERESTART;
> + goto out;
> }
> if (!dev->present) {
> //The device was unplugged
> - return -ENODEV;
> + result = -ENODEV;
> + goto out;
> }
> if (read_idx == -1) {
> // Can this happen ???
> + mutex_unlock(&dev->mutex);
> return 0;
> }
> }
> @@ -324,13 +340,16 @@ static ssize_t iowarrior_read(struct file *file, char __user *buffer,
>
> offset = read_idx * (dev->report_size + 1);
> if (copy_to_user(buffer, dev->read_queue + offset, count)) {
> - return -EFAULT;
> + result = -EFAULT;
> + goto out;
> }
> } while (atomic_read(&dev->overflow_flag));
>
> read_idx = ++read_idx == MAX_INTERRUPT_BUFFER ? 0 : read_idx;
> atomic_set(&dev->read_idx, read_idx);
> - return count;
> +out:
> + mutex_unlock(&dev->mutex);
> + return result < 0 ? result : count;
> }
>
> /*
> --
> 2.45.2
>
>