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SubjectRe: [PATCH 2/2] ax25: add refcount in ax25_dev to avoid UAF bugs
On Fri, Jan 28, 2022 at 12:47:16PM +0800, Duoming Zhou wrote:
> diff --git a/include/net/ax25.h b/include/net/ax25.h
> index 526e4958919..50b417df622 100644
> --- a/include/net/ax25.h
> +++ b/include/net/ax25.h
> @@ -239,6 +239,7 @@ typedef struct ax25_dev {
> #if defined(CONFIG_AX25_DAMA_SLAVE) || defined(CONFIG_AX25_DAMA_MASTER)
> ax25_dama_info dama;
> #endif
> + refcount_t refcount;
> } ax25_dev;
>
> typedef struct ax25_cb {
> @@ -293,6 +294,15 @@ static __inline__ void ax25_cb_put(ax25_cb *ax25)
> }
> }
>
> +#define ax25_dev_hold(__ax25_dev) \
> + refcount_inc(&((__ax25_dev)->refcount))

Make this an inline function.

> +
> +static __inline__ void ax25_dev_put(ax25_dev *ax25_dev)

Please run checkpatch.pl --strict on your patches. s/__inline__/inline/

> +{
> + if (refcount_dec_and_test(&ax25_dev->refcount)) {
> + kfree(ax25_dev);
> + }

Delete the extra curly braces.

> +}
> static inline __be16 ax25_type_trans(struct sk_buff *skb, struct net_device *dev)
> {
> skb->dev = dev;
> diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
> index 44a8730c26a..32f61978ff2 100644
> --- a/net/ax25/af_ax25.c
> +++ b/net/ax25/af_ax25.c
> @@ -91,6 +91,7 @@ static void ax25_kill_by_device(struct net_device *dev)
> spin_unlock_bh(&ax25_list_lock);
> lock_sock(sk);
> s->ax25_dev = NULL;
> + ax25_dev_put(ax25_dev);
> release_sock(sk);
> ax25_disconnect(s, ENETUNREACH);
> spin_lock_bh(&ax25_list_lock);
> @@ -439,6 +440,7 @@ static int ax25_ctl_ioctl(const unsigned int cmd, void __user *arg)
> }
>
> out_put:
> + ax25_dev_put(ax25_dev);

The ax25_ctl_ioctl() has a ton of reference leak paths now. Almost
every return -ESOMETHING needs to be fixed.

> ax25_cb_put(ax25);
> return ret;
>
> diff --git a/net/ax25/ax25_dev.c b/net/ax25/ax25_dev.c
> index 256fadb94df..770b787fb7b 100644
> --- a/net/ax25/ax25_dev.c
> +++ b/net/ax25/ax25_dev.c
> @@ -37,6 +37,7 @@ ax25_dev *ax25_addr_ax25dev(ax25_address *addr)
> for (ax25_dev = ax25_dev_list; ax25_dev != NULL; ax25_dev = ax25_dev->next)
> if (ax25cmp(addr, (const ax25_address *)ax25_dev->dev->dev_addr) == 0) {
> res = ax25_dev;
> + ax25_dev_hold(ax25_dev);
> }
> spin_unlock_bh(&ax25_dev_lock);
>
> @@ -56,6 +57,7 @@ void ax25_dev_device_up(struct net_device *dev)
> return;
> }
>
> + refcount_set(&ax25_dev->refcount, 1);
> dev->ax25_ptr = ax25_dev;
> ax25_dev->dev = dev;
> dev_hold_track(dev, &ax25_dev->dev_tracker, GFP_ATOMIC);
> @@ -83,6 +85,7 @@ void ax25_dev_device_up(struct net_device *dev)
> spin_lock_bh(&ax25_dev_lock);
> ax25_dev->next = ax25_dev_list;
> ax25_dev_list = ax25_dev;
> + ax25_dev_hold(ax25_dev);
> spin_unlock_bh(&ax25_dev_lock);
>
> ax25_register_dev_sysctl(ax25_dev);
> @@ -112,20 +115,22 @@ void ax25_dev_device_down(struct net_device *dev)
>
> if ((s = ax25_dev_list) == ax25_dev) {
> ax25_dev_list = s->next;
> + ax25_dev_put(ax25_dev);

Do we not have to call ax25_dev_hold(s->next)?

> spin_unlock_bh(&ax25_dev_lock);
> dev->ax25_ptr = NULL;
> dev_put_track(dev, &ax25_dev->dev_tracker);
> - kfree(ax25_dev);
> + ax25_dev_put(ax25_dev);
> return;
> }
>
> while (s != NULL && s->next != NULL) {
> if (s->next == ax25_dev) {
> s->next = ax25_dev->next;
> + ax25_dev_put(ax25_dev);

ax25_dev_hold(ax25_dev->next)?

> spin_unlock_bh(&ax25_dev_lock);
> dev->ax25_ptr = NULL;
> dev_put_track(dev, &ax25_dev->dev_tracker);
> - kfree(ax25_dev);
> + ax25_dev_put(ax25_dev);
> return;
> }
>
> @@ -133,6 +138,7 @@ void ax25_dev_device_down(struct net_device *dev)
> }
> spin_unlock_bh(&ax25_dev_lock);
> dev->ax25_ptr = NULL;
> + ax25_dev_put(ax25_dev);
> }
>
> int ax25_fwd_ioctl(unsigned int cmd, struct ax25_fwd_struct *fwd)
> @@ -149,6 +155,7 @@ int ax25_fwd_ioctl(unsigned int cmd, struct ax25_fwd_struct *fwd)
> if (ax25_dev->forward != NULL)
> return -EINVAL;

Every return -ERROR; in this function leaks reference counts. This one
should drop the reference for both fwd_dev and ax25_dev.


> ax25_dev->forward = fwd_dev->dev;
> + ax25_dev_put(fwd_dev);
> break;
>
> case SIOCAX25DELFWD:

regards,
dan carpenter

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