On Thu, Jan 28, 2021 at 12:55 PM Jakub Kicinski <k...@kernel.org> wrote:
>
> On Sat, 23 Jan 2021 17:30:49 -0800 Cong Wang wrote:
> > From: Cong Wang <cong.w...@bytedance.com>
> >
> > dev_ifsioc_locked() is called with only RCU read lock, so when
> > there is a parallel writer changing the mac address, it could
> > get a partially updated mac address, as shown below:
> >
> > Thread 1 Thread 2
> > // eth_commit_mac_addr_change()
> > memcpy(dev->dev_addr, addr->sa_data, ETH_ALEN);
> > // dev_ifsioc_locked()
> > memcpy(ifr->ifr_hwaddr.sa_data,
> > dev->dev_addr,...);
> >
> > Close this race condition by guarding them with a RW semaphore,
> > like netdev_get_name(). The writers take RTNL anyway, so this
> > will not affect the slow path.
> >
> > Fixes: 3710becf8a58 ("net: RCU locking for simple ioctl()")
> > Reported-by: "Gong, Sishuai" <sish...@purdue.edu>
> > Cc: Eric Dumazet <eric.duma...@gmail.com>
> > Signed-off-by: Cong Wang <cong.w...@bytedance.com>
>
> The addition of the write lock scares me a little for a fix, there's a
> lot of code which can potentially run under the callbacks and notifiers
> there.
>
> What about using a seqlock?
Actually I did use seqlock in my initial version (not posted), it does not
allow blocking inside write_seqlock() protection, so I have to change
to rwsem.
Thanks.
