Re: [PATCH 5.10 09/38] llc: fix netdevice reference leaks in llc_ui_bind()

Pavel Machek
2022-03-26T20:10:32Z

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Hi!

> From: Eric Dumazet <edumazet@google.com>
>
> commit 764f4eb6846f5475f1244767d24d25dd86528a4a upstream.
>
> Whenever llc_ui_bind() and/or llc_ui_autobind()
> took a reference on a netdevice but subsequently fail,
> they must properly release their reference
> or risk the infamous message from unregister_netdevice()
> at device dismantle.
>
> unregister_netdevice: waiting for eth0 to become free. Usage count =
> 3

Can someone check this? AFAICT this is buggy.

static int llc_ui_autobind(struct socket *sock, struct sockaddr_llc *addr)
{
struct sock *sk = sock->sk;
struct llc_sock *llc = llc_sk(sk);
struct llc_sap *sap;
int rc = -EINVAL;

if (!sock_flag(sk, SOCK_ZAPPED))
goto out;

There are 'goto out's from both before dev_get() and after it,
dev_put() will be called with NULL pointer. dev_put() can't handle
NULL at least in the old kernels... this is simply confused.

Mainline has dev_put_track() there, but I see same confusion.

Best regards,
Pavel

> --- a/net/llc/af_llc.c
> +++ b/net/llc/af_llc.c
> @@ -311,6 +311,10 @@ static int llc_ui_autobind(struct socket
> sock_reset_flag(sk, SOCK_ZAPPED);
> rc = 0;
> out:
> + if (rc) {
> + dev_put(llc->dev);
> + llc->dev = NULL;
> + }
> return rc;
> }
>
> @@ -409,6 +413,10 @@ static int llc_ui_bind(struct socket *so
> out_put:
> llc_sap_put(sap);
> out:
> + if (rc) {
> + dev_put(llc->dev);
> + llc->dev = NULL;
> + }
> release_sock(sk);
> return rc;
> }
>

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