Re: [PATCH net-next] ip6_tunnel: sit: proper dev_{hold|put} in ndo_[un]init methods

On Wed, Mar 31, 2021 at 8:00 AM Eric Dumazet [off-list ref] wrote:

On Tue, Mar 30, 2021 at 8:45 AM Eric Dumazet [off-list ref] wrote:

quoted

From: Eric Dumazet <redacted>

Same reasons than for the previous commits :
6289a98f0817 ("sit: proper dev_{hold|put} in ndo_[un]init methods")
40cb881b5aaa ("ip6_vti: proper dev_{hold|put} in ndo_[un]init methods")
7f700334be9a ("ip6_gre: proper dev_{hold|put} in ndo_[un]init methods")

After adopting CONFIG_PCPU_DEV_REFCNT=n option, syzbot was able to trigger
a warning [1]

Issue here is that:

- all dev_put() should be paired with a corresponding prior dev_hold().

- A driver doing a dev_put() in its ndo_uninit() MUST also
  do a dev_hold() in its ndo_init(), only when ndo_init()
  is returning 0.

Otherwise, register_netdevice() would call ndo_uninit()
in its error path and release a refcount too soon.

Note to David & Jakub

Can you merge this patch so that I can send my global fix for fallback
tunnels, with a correct Fixes: tag for this patch ?

Thanks !

Forgot to attach what the global fix would look like :