On Friday 09/05 at 10:25 -0700, Breno Leitao wrote:
> commit efa95b01da18 ("netpoll: fix use after free") incorrectly
> ignored the refcount and prematurely set dev->npinfo to NULL during
> netpoll cleanup, leading to improper behavior and memory leaks.
>
> Scenario causing lack of proper cleanup:
>
> 1) A netpoll is associated with a NIC (e.g., eth0) and netdev->npinfo is
> allocated, and refcnt = 1
> - Keep in mind that npinfo is shared among all netpoll instances. In
> this case, there is just one.
>
> 2) Another netpoll is also associated with the same NIC and
> npinfo->refcnt += 1.
> - Now dev->npinfo->refcnt = 2;
> - There is just one npinfo associated to the netdev.
>
> 3) When the first netpolls goes to clean up:
> - The first cleanup succeeds and clears np->dev->npinfo, ignoring
> refcnt.
> - It basically calls `RCU_INIT_POINTER(np->dev->npinfo, NULL);`
> - Set dev->npinfo = NULL, without proper cleanup
> - No ->ndo_netpoll_cleanup() is either called
>
> 4) Now the second target tries to clean up
> - The second cleanup fails because np->dev->npinfo is already NULL.
> * In this case, ops->ndo_netpoll_cleanup() was never called, and
> the skb pool is not cleaned as well (for the second netpoll
> instance)
> - This leaks npinfo and skbpool skbs, which is clearly reported by
> kmemleak.
>
> Revert commit efa95b01da18 ("netpoll: fix use after free") and adds
> clarifying comments emphasizing that npinfo cleanup should only happen
> once the refcount reaches zero, ensuring stable and correct netpoll
> behavior.
This makes sense to me.
Just curious, did you try the original OOPS reproducer?
https://lore.kernel.org/lkml/96b940137a50e5c387687bb4f57de8b0435a653f.1404857349.git.de...@googlers.com/
I wonder if there might be a demon lurking in bonding+netpoll that this
was papering over? Not a reason not to fix the leaks IMO, I'm just
curious, I don't want to spend time on it if you already did :)
The discussion on v1 isn't enlightening either:
https://lore.kernel.org/lkml/0f692012238337f2c40893319830ae042523ce18.1404172155.git.de...@googlers.com/
Thanks,
Calvin
> Cc: sta...@vger.kernel.org
> Cc: j...@jvosburgh.net
> Fixes: efa95b01da18 ("netpoll: fix use after free")
> Signed-off-by: Breno Leitao <lei...@debian.org>
> ---
> net/core/netpoll.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/netpoll.c b/net/core/netpoll.c
> index 5f65b62346d4e..19676cd379640 100644
> --- a/net/core/netpoll.c
> +++ b/net/core/netpoll.c
> @@ -815,6 +815,10 @@ static void __netpoll_cleanup(struct netpoll *np)
> if (!npinfo)
> return;
>
> + /* At this point, there is a single npinfo instance per netdevice, and
> + * its refcnt tracks how many netpoll structures are linked to it. We
> + * only perform npinfo cleanup when the refcnt decrements to zero.
> + */
> if (refcount_dec_and_test(&npinfo->refcnt)) {
> const struct net_device_ops *ops;
>
> @@ -824,8 +828,7 @@ static void __netpoll_cleanup(struct netpoll *np)
>
> RCU_INIT_POINTER(np->dev->npinfo, NULL);
> call_rcu(&npinfo->rcu, rcu_cleanup_netpoll_info);
> - } else
> - RCU_INIT_POINTER(np->dev->npinfo, NULL);
> + }
>
> skb_pool_flush(np);
> }
>
> --
> 2.47.3
>
