2021-11-11 14:00:23

by Lin Ma

Subject: [PATCH v0] hamradio: delete unnecessary free_netdev()

The former patch "defer 6pack kfree after unregister_netdev" adds
free_netdev() function in sixpack_close(), which is a bad copy from the
similar code in mkiss_close(). However, this free is unnecessary as the
flag needs_free_netdev is set to true in sp_setup(), hence the
unregister_netdev() will free the netdev automatically.

Signed-off-by: Lin Ma <[email protected]>
---
drivers/net/hamradio/6pack.c | 2 --
1 file changed, 2 deletions(-)

diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c
index bfdf89e54752..180c8f08169b 100644
--- a/drivers/net/hamradio/6pack.c
+++ b/drivers/net/hamradio/6pack.c
@@ -677,8 +677,6 @@ static void sixpack_close(struct tty_struct *tty)
/* Free all 6pack frame buffers after unreg. */
kfree(sp->rbuff);
kfree(sp->xbuff);
-
- free_netdev(sp->dev);
}

/* Perform I/O control on an active 6pack channel. */
--
2.33.1

2021-11-11 14:04:49

by Jakub Kicinski

Subject: Re: [PATCH v0] hamradio: delete unnecessary free_netdev()

On Thu, 11 Nov 2021 22:00:07 +0800 Lin Ma wrote:
> The former patch "defer 6pack kfree after unregister_netdev" adds
> free_netdev() function in sixpack_close(), which is a bad copy from the
> similar code in mkiss_close(). However, this free is unnecessary as the
> flag needs_free_netdev is set to true in sp_setup(), hence the
> unregister_netdev() will free the netdev automatically.
>
> Signed-off-by: Lin Ma <[email protected]>
> ---
> drivers/net/hamradio/6pack.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c
> index bfdf89e54752..180c8f08169b 100644
> --- a/drivers/net/hamradio/6pack.c
> +++ b/drivers/net/hamradio/6pack.c
> @@ -677,8 +677,6 @@ static void sixpack_close(struct tty_struct *tty)
> /* Free all 6pack frame buffers after unreg. */
> kfree(sp->rbuff);
> kfree(sp->xbuff);
> -
> - free_netdev(sp->dev);

sp is netdev_priv() tho, so this is now a UAF. I'd go for removing the
needs_free_netdev = true instead.

> }
>
> /* Perform I/O control on an active 6pack channel. */

2021-11-11 14:08:35

by Lin Ma

Subject: Re: Re: [PATCH v0] hamradio: delete unnecessary free_netdev()

Hi Jakub

> On Thu, 11 Nov 2021 22:00:07 +0800 Lin Ma wrote:
> > The former patch "defer 6pack kfree after unregister_netdev" adds
> > free_netdev() function in sixpack_close(), which is a bad copy from the
> > similar code in mkiss_close(). However, this free is unnecessary as the
> > flag needs_free_netdev is set to true in sp_setup(), hence the
> > unregister_netdev() will free the netdev automatically.
> >
> > Signed-off-by: Lin Ma <[email protected]>
> > ---
> > drivers/net/hamradio/6pack.c | 2 --
> > 1 file changed, 2 deletions(-)
> >
> > diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c
> > index bfdf89e54752..180c8f08169b 100644
> > --- a/drivers/net/hamradio/6pack.c
> > +++ b/drivers/net/hamradio/6pack.c
> > @@ -677,8 +677,6 @@ static void sixpack_close(struct tty_struct *tty)
> > /* Free all 6pack frame buffers after unreg. */
> > kfree(sp->rbuff);
> > kfree(sp->xbuff);
> > -
> > - free_netdev(sp->dev);
>
> sp is netdev_priv() tho, so this is now a UAF. I'd go for removing the
> needs_free_netdev = true instead.
>
> > }
> >
> > /* Perform I/O control on an active 6pack channel. */

Okay, that make senses, wait a minute.

Thanks
Lin