[PATCH net 1/1] net: usb: rtl8150: break cycle between tasklet and URB

[PATCH net 1/1] net: usb: rtl8150: break cycle between tasklet and URB

[Oliver Neukum]

The tasklet can resubmit the URB, which in turn can
resubmit the tasklet. The cycle needs to be broken.
The simplest way to do so is to prevent the resubmission
of the URBs by poisoning them.

Fixes: eff674a514bd3 ("USB: rtl8150_disconnect() needs tasklet_kill()")
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 drivers/net/usb/rtl8150.c | 31 ++++++++++++++++++++++++++-----
 1 file changed, 26 insertions(+), 5 deletions(-)

diff --git a/drivers/net/usb/rtl8150.c b/drivers/net/usb/rtl8150.c
index d51e43170e03..846e6329d571 100644
--- a/drivers/net/usb/rtl8150.c
+++ b/drivers/net/usb/rtl8150.c
@@ -343,6 +343,13 @@ static int alloc_all_urbs(rtl8150_t * dev)
 		return 0;
 	}
 
+	/*
+	 * They need to be blocked so that open()
+	 * can unblock them
+	 */
+	usb_block_urb(dev->rx_urb);
+	usb_block_urb(dev->tx_urb);
+	usb_block_urb(dev->intr_urb);
 	return 1;
 }
 
@@ -353,11 +360,18 @@ static void free_all_urbs(rtl8150_t * dev)
 	usb_free_urb(dev->intr_urb);
 }
 
+static void reenable_all_urbs(rtl8150_t *dev)
+{
+	usb_unpoison_urb(dev->rx_urb);
+	usb_unpoison_urb(dev->tx_urb);
+	usb_unpoison_urb(dev->intr_urb);
+}
+
 static void unlink_all_urbs(rtl8150_t * dev)
 {
-	usb_kill_urb(dev->rx_urb);
-	usb_kill_urb(dev->tx_urb);
-	usb_kill_urb(dev->intr_urb);
+	usb_poison_urb(dev->rx_urb);
+	usb_poison_urb(dev->tx_urb);
+	usb_poison_urb(dev->intr_urb);
 }
 
 static inline struct sk_buff *pull_skb(rtl8150_t *dev)
@@ -425,6 +439,11 @@ static void read_bulk_callback(struct urb *urb)
 	netdev->stats.rx_bytes += pkt_len;
 
 	spin_lock_irqsave(&dev->rx_pool_lock, flags);
+	/* prevent an eteral loop */
+	if (test_bit(RTL8150_UNPLUG, &dev->flags)) {
+		spin_unlock_irqrestore(&dev->rx_pool_lock, flags);
+		return;
+	}
 	skb = pull_skb(dev);
 	spin_unlock_irqrestore(&dev->rx_pool_lock, flags);
 	if (!skb)
@@ -518,7 +537,7 @@ static void intr_callback(struct urb *urb)
 	res = usb_submit_urb (urb, GFP_ATOMIC);
 	if (res == -ENODEV)
 		netif_device_detach(dev->netdev);
-	else if (res)
+	else if (res != -EPERM)
 		dev_err(&dev->udev->dev,
 			"can't resubmit intr, %s-%s/input0, status %d\n",
 			dev->udev->bus->bus_name, dev->udev->devpath, res);
@@ -751,6 +770,7 @@ static int rtl8150_open(struct net_device *netdev)
 	if (!dev->rx_skb)
 		return -ENOMEM;
 
+	reenable_all_urbs(dev);
 	set_registers(dev, IDR, 6, netdev->dev_addr);
 
 	usb_fill_bulk_urb(dev->rx_urb, dev->udev, usb_rcvbulkpipe(dev->udev, 1),
@@ -969,8 +989,9 @@ static void rtl8150_disconnect(struct usb_interface *intf)
 	if (dev) {
 		set_bit(RTL8150_UNPLUG, &dev->flags);
 		tasklet_kill(&dev->tl);
-		unregister_netdev(dev->netdev);
 		unlink_all_urbs(dev);
+		tasklet_kill(&dev->tl);
+		unregister_netdev(dev->netdev);
 		free_all_urbs(dev);
 		free_skb_pool(dev);
 		dev_kfree_skb(dev->rx_skb);
-- 
2.56.0

Re: [PATCH net 1/1] net: usb: rtl8150: break cycle between tasklet and URB

[netdev-bot+sinfo]

Hi!

This is an automated message. This series looks like a fix, but its
commit messages seem to be missing some information:

 - How the issue was discovered, e.g. hit in production, hit during
   development, syzbot report, manual code inspection, LLM or static
   analysis tool scan.

 - Whether the issue was actually triggered, or is only theoretical
   (e.g. found by LLM and not proven at runtime). If it was triggered
   please include the symptoms, like the stack trace or kernel messages.

Please do not repost the series just to address the above. Instead,
reply to this email with the missing information, so that reviewers
can take it into account. If the series needs another revision for
other reasons, please include the information in the commit messages
then.

The evaluation is done by an LLM so it may be wrong, if you think
that is the case please reply and explain.

Re: [PATCH net 1/1] net: usb: rtl8150: break cycle between tasklet and URB

[Oliver Neukum]

On 12.11.26 11:52, netdev-bot+sinfo@kernel.org wrote:
  
> Please do not repost the series just to address the above. Instead,
> reply to this email with the missing information, so that reviewers
> can take it into account. If the series needs another revision for
> other reasons, please include the information in the commit messages
> then.

This is in response to a patch by Myeonghung Pak, whose patch
tried to fix the issue, but failed to, as Sashiko found out.

	HTH
		Oliver

Re: [PATCH net 1/1] net: usb: rtl8150: break cycle between tasklet and URB

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 4 potential
issues to consider:
- [High] net: usb: rtl8150: infinite tasklet loop on -EPERM in
  rx_fixup()
- [High] net: usb: rtl8150: double free of dev->rx_skb on unplug in
  read_bulk_callback()
- [Medium] net: usb: rtl8150: false dev_err() on res == 0 in
  intr_callback()
- [Medium] net: usb: rtl8150: unbalanced URB reject count on error in
  rtl8150_open()
It also noticed 1 related pre-existing issue this patch does not
introduce:
- [High] net: usb: rtl8150: dangling rx_skb pointer in
  read_bulk_callback() [1]
--

commit bed5b8274af4c5f050a94925def40d4d88f1a
Author: Oliver Neukum <oneukum@suse.com>

net: usb: rtl8150: break cycle between tasklet and URB

This commit replaces usb_kill_urb() with usb_poison_urb() in
unlink_all_urbs(), blocks URBs at allocation time and unpoisons them on
open, and checks RTL8150_UNPLUG in read_bulk_callback() to break the
resubmission cycle between dev->rx_urb and dev->tl on disconnect.

> diff --git a/drivers/net/usb/rtl8150.c b/drivers/net/usb/rtl8150.c
> index d51e43170e033..846e6329d571c 100644
> --- a/drivers/net/usb/rtl8150.c
> +++ b/drivers/net/usb/rtl8150.c
> @@ -343,6 +343,13 @@ static int alloc_all_urbs(rtl8150_t * dev)
>  		return 0;
>  	}
>  
> +	/*
> +	 * They need to be blocked so that open()
> +	 * can unblock them
> +	 */
> +	usb_block_urb(dev->rx_urb);
> +	usb_block_urb(dev->tx_urb);
> +	usb_block_urb(dev->intr_urb);
>  	return 1;
>  }
>  
> @@ -353,11 +360,18 @@ static void free_all_urbs(rtl8150_t * dev)
>  	usb_free_urb(dev->intr_urb);
>  }
>  
> +static void reenable_all_urbs(rtl8150_t *dev)
> +{
> +	usb_unpoison_urb(dev->rx_urb);
> +	usb_unpoison_urb(dev->tx_urb);
> +	usb_unpoison_urb(dev->intr_urb);
> +}
> +
>  static void unlink_all_urbs(rtl8150_t * dev)
>  {
> -	usb_kill_urb(dev->rx_urb);
> -	usb_kill_urb(dev->tx_urb);
> -	usb_kill_urb(dev->intr_urb);
> +	usb_poison_urb(dev->rx_urb);
> +	usb_poison_urb(dev->tx_urb);
> +	usb_poison_urb(dev->intr_urb);
>  }

[Severity: High]
Can poisoning dev->rx_urb cause rx_fixup() to spin in an infinite tasklet
loop on -EPERM?

Once unlink_all_urbs() poisons dev->rx_urb in rtl8150_close() or
rtl8150_disconnect(), usb_submit_urb(dev->rx_urb, GFP_ATOMIC) returns -EPERM.
Neither read_bulk_callback() nor rx_fixup() ignores -EPERM, and rx_fixup()
never checks RTL8150_UNPLUG:

drivers/net/usb/rtl8150.c:rx_fixup() {
    ...
	if (test_bit(RX_URB_FAIL, &dev->flags))
		if (dev->rx_skb)
			goto try_again;
    ...
try_again:
	status = usb_submit_urb(dev->rx_urb, GFP_ATOMIC);
	if (status == -ENODEV) {
		netif_device_detach(dev->netdev);
	} else if (status) {
		set_bit(RX_URB_FAIL, &dev->flags);
		goto tlsched;
	}
    ...
tlsched:
	tasklet_schedule(&dev->tl);
}

If dev->tl is scheduled when unlink_all_urbs() poisons dev->rx_urb (or if
read_bulk_callback() hits -EPERM at goon: during rtl8150_close() where
RTL8150_UNPLUG is not set), rx_fixup() sets RX_URB_FAIL and reschedules
dev->tl in a tight softirq loop, locking up softirq processing on Close and
hanging tasklet_kill(&dev->tl) in rtl8150_disconnect().

> @@ -425,6 +439,11 @@ static void read_bulk_callback(struct urb *urb)
>  	netdev->stats.rx_bytes += pkt_len;
>  
>  	spin_lock_irqsave(&dev->rx_pool_lock, flags);
> +	/* prevent an eteral loop */
> +	if (test_bit(RTL8150_UNPLUG, &dev->flags)) {
> +		spin_unlock_irqrestore(&dev->rx_pool_lock, flags);
> +		return;
> +	}
>  	skb = pull_skb(dev);
>  	spin_unlock_irqrestore(&dev->rx_pool_lock, flags);
>  	if (!skb)

[Severity: High]
Does returning here when RTL8150_UNPLUG is set cause a double free of
dev->rx_skb?

Just before taking dev->rx_pool_lock, read_bulk_callback() passes
dev->rx_skb to netif_rx().  Returning without clearing dev->rx_skb to NULL
leaves the consumed skb pointer in dev->rx_skb, which rtl8150_disconnect()
then frees a second time via dev_kfree_skb(dev->rx_skb).

[Severity: High]
This problem wasn't introduced by this patch, but read_bulk_callback() also
leaves [1] dev->rx_skb holding a dangling pointer to the skb handed to
netif_rx() whenever pull_skb() returns NULL and jumps to resched:.  If the
device is disconnected before rx_fixup() replaces dev->rx_skb,
rtl8150_disconnect() double frees dev->rx_skb, and if the device is closed
and reopened or suspended and resumed in that state, rtl8150_open() or
rtl8150_resume() resubmits dev->rx_urb using the freed skb buffer.

> @@ -518,7 +537,7 @@ static void intr_callback(struct urb *urb)
>  	res = usb_submit_urb (urb, GFP_ATOMIC);
>  	if (res == -ENODEV)
>  		netif_device_detach(dev->netdev);
> -	else if (res)
> +	else if (res != -EPERM)
>  		dev_err(&dev->udev->dev,
>  			"can't resubmit intr, %s-%s/input0, status %d\n",
>  			dev->udev->bus->bus_name, dev->udev->devpath, res);

[Severity: Medium]
Doesn't "else if (res != -EPERM)" evaluate to true when usb_submit_urb()
succeeds with res == 0?  That logs a false dev_err() on every interrupt URB
completion unless the check is "else if (res && res != -EPERM)".

> @@ -751,6 +770,7 @@ static int rtl8150_open(struct net_device *netdev)
>  	if (!dev->rx_skb)
>  		return -ENOMEM;
>  
> +	reenable_all_urbs(dev);
>  	set_registers(dev, IDR, 6, netdev->dev_addr);
>  
>  	usb_fill_bulk_urb(dev->rx_urb, dev->udev, usb_rcvbulkpipe(dev->udev, 1),

[Severity: Medium]
What happens to the URB reject count if usb_submit_urb() fails in
rtl8150_open()?

reenable_all_urbs() decrements urb->reject from 1 to 0 on all three URBs,
and the error paths in rtl8150_open() return without calling
unlink_all_urbs() to re-poison them (only calling usb_kill_urb(dev->rx_urb)
when dev->intr_urb submission fails):

drivers/net/usb/rtl8150.c:rtl8150_open() {
    ...
	if ((res = usb_submit_urb(dev->rx_urb, GFP_KERNEL))) {
		if (res == -ENODEV)
			netif_device_detach(dev->netdev);
		dev_warn(&netdev->dev, "rx_urb submit failed: %d\n", res);
		return res;
	}
    ...
	if ((res = usb_submit_urb(dev->intr_urb, GFP_KERNEL))) {
		if (res == -ENODEV)
			netif_device_detach(dev->netdev);
		dev_warn(&netdev->dev, "intr_urb submit failed: %d\n", res);
		usb_kill_urb(dev->rx_urb);
		return res;
	}
    ...
}

Because rtl8150_close() is not called when rtl8150_open() fails, the next
rtl8150_open() call decrements urb->reject from 0 to -1, causing all
subsequent usb_submit_urb() calls to fail with -EPERM and causing a later
unlink_all_urbs() to increment urb->reject back to 0 instead of poisoning
the URBs.

[1] https://sashiko.dev/#/bug/linux-361a8ebc-4be5-4126-a2d9-b88d108064a9

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261112104548.693456-1-oneukum@suse.com?part=1