* Re: [PATCH] usb: gadget: u_ether: Fix race between gether_disconnect and eth_stop
2026-03-11 9:12 [PATCH] usb: gadget: u_ether: Fix race between gether_disconnect and eth_stop Kuen-Han Tsai
@ 2026-03-26 7:10 ` Dayu Jiang
2026-03-26 7:16 ` Dayu Jiang
` (3 subsequent siblings)
4 siblings, 0 replies; 7+ messages in thread
From: Dayu Jiang @ 2026-03-26 7:10 UTC (permalink / raw)
To: Greg Kroah-Hartman, David Brownell
Cc: Kuen-Han Tsai, linux-usb, linux-kernel, stable
On Wed, Mar 11, 2026 at 05:12:15PM +0800, Kuen-Han Tsai wrote:
> A race condition between gether_disconnect() and eth_stop() leads to a
> NULL pointer dereference. Specifically, if eth_stop() is triggered
> concurrently while gether_disconnect() is tearing down the endpoints,
> eth_stop() attempts to access the cleared endpoint descriptor, causing
> the following NPE:
>
> Unable to handle kernel NULL pointer dereference
> Call trace:
> __dwc3_gadget_ep_enable+0x60/0x788
> dwc3_gadget_ep_enable+0x70/0xe4
> usb_ep_enable+0x60/0x15c
> eth_stop+0xb8/0x108
>
> Because eth_stop() crashes while holding the dev->lock, the thread
> running gether_disconnect() fails to acquire the same lock and spins
> forever, resulting in a hardlockup:
>
> Core - Debugging Information for Hardlockup core(7)
> Call trace:
> queued_spin_lock_slowpath+0x94/0x488
> _raw_spin_lock+0x64/0x6c
> gether_disconnect+0x19c/0x1e8
> ncm_set_alt+0x68/0x1a0
> composite_setup+0x6a0/0xc50
>
> The root cause is that the clearing of dev->port_usb in
> gether_disconnect() is delayed until the end of the function.
>
> Move the clearing of dev->port_usb to the very beginning of
> gether_disconnect() while holding dev->lock. This cuts off the link
> immediately, ensuring eth_stop() will see dev->port_usb as NULL and
> safely bail out.
Hi Greg,
Hit the same issue during NCM switch stress test.
Can you take a look at this patch and check if it’s ready for merge?
Thanks,
Dayu Jiang
>
> Fixes: 2b3d942c4878 ("usb ethernet gadget: split out network core")
> Cc: stable@vger.kernel.org
> Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
> ---
> drivers/usb/gadget/function/u_ether.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
> index 338f6e2a85a9..2c970a0eafd9 100644
> --- a/drivers/usb/gadget/function/u_ether.c
> +++ b/drivers/usb/gadget/function/u_ether.c
> @@ -1246,6 +1246,11 @@ void gether_disconnect(struct gether *link)
>
> DBG(dev, "%s\n", __func__);
>
> + spin_lock(&dev->lock);
> + dev->port_usb = NULL;
> + link->is_suspend = false;
> + spin_unlock(&dev->lock);
> +
> netif_stop_queue(dev->net);
> netif_carrier_off(dev->net);
>
> @@ -1283,11 +1288,6 @@ void gether_disconnect(struct gether *link)
> dev->header_len = 0;
> dev->unwrap = NULL;
> dev->wrap = NULL;
> -
> - spin_lock(&dev->lock);
> - dev->port_usb = NULL;
> - link->is_suspend = false;
> - spin_unlock(&dev->lock);
> }
> EXPORT_SYMBOL_GPL(gether_disconnect);
>
>
> ---
> base-commit: 1be3b77de4eb89af8ae2fd6610546be778e25589
> change-id: 20260311-gether-disconnect-npe-5861d9831dff
>
> Best regards,
> --
> Kuen-Han Tsai <khtsai@google.com>
>
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] usb: gadget: u_ether: Fix race between gether_disconnect and eth_stop
2026-03-11 9:12 [PATCH] usb: gadget: u_ether: Fix race between gether_disconnect and eth_stop Kuen-Han Tsai
2026-03-26 7:10 ` Dayu Jiang
@ 2026-03-26 7:16 ` Dayu Jiang
2026-03-26 7:53 ` Dayu Jiang
` (2 subsequent siblings)
4 siblings, 0 replies; 7+ messages in thread
From: Dayu Jiang @ 2026-03-26 7:16 UTC (permalink / raw)
To: Greg Kroah-Hartman, Kuen-Han Tsai
Cc: David Brownell, linux-usb, linux-kernel, stable
On Wed, Mar 11, 2026 at 05:12:15PM +0800, Kuen-Han Tsai wrote:
> A race condition between gether_disconnect() and eth_stop() leads to a
> NULL pointer dereference. Specifically, if eth_stop() is triggered
> concurrently while gether_disconnect() is tearing down the endpoints,
> eth_stop() attempts to access the cleared endpoint descriptor, causing
> the following NPE:
>
> Unable to handle kernel NULL pointer dereference
> Call trace:
> __dwc3_gadget_ep_enable+0x60/0x788
> dwc3_gadget_ep_enable+0x70/0xe4
> usb_ep_enable+0x60/0x15c
> eth_stop+0xb8/0x108
>
Hi Greg,
Hit the same issue during NCM switch stress test.
Can you take a look at this patch and check if it’s ready for merge?
Thanks,
Dayu Jiang
> Because eth_stop() crashes while holding the dev->lock, the thread
> running gether_disconnect() fails to acquire the same lock and spins
> forever, resulting in a hardlockup:
>
> Core - Debugging Information for Hardlockup core(7)
> Call trace:
> queued_spin_lock_slowpath+0x94/0x488
> _raw_spin_lock+0x64/0x6c
> gether_disconnect+0x19c/0x1e8
> ncm_set_alt+0x68/0x1a0
> composite_setup+0x6a0/0xc50
>
> The root cause is that the clearing of dev->port_usb in
> gether_disconnect() is delayed until the end of the function.
>
> Move the clearing of dev->port_usb to the very beginning of
> gether_disconnect() while holding dev->lock. This cuts off the link
> immediately, ensuring eth_stop() will see dev->port_usb as NULL and
> safely bail out.
>
> Fixes: 2b3d942c4878 ("usb ethernet gadget: split out network core")
> Cc: stable@vger.kernel.org
> Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
> ---
> drivers/usb/gadget/function/u_ether.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
> index 338f6e2a85a9..2c970a0eafd9 100644
> --- a/drivers/usb/gadget/function/u_ether.c
> +++ b/drivers/usb/gadget/function/u_ether.c
> @@ -1246,6 +1246,11 @@ void gether_disconnect(struct gether *link)
>
> DBG(dev, "%s\n", __func__);
>
> + spin_lock(&dev->lock);
> + dev->port_usb = NULL;
> + link->is_suspend = false;
> + spin_unlock(&dev->lock);
> +
> netif_stop_queue(dev->net);
> netif_carrier_off(dev->net);
>
> @@ -1283,11 +1288,6 @@ void gether_disconnect(struct gether *link)
> dev->header_len = 0;
> dev->unwrap = NULL;
> dev->wrap = NULL;
> -
> - spin_lock(&dev->lock);
> - dev->port_usb = NULL;
> - link->is_suspend = false;
> - spin_unlock(&dev->lock);
> }
> EXPORT_SYMBOL_GPL(gether_disconnect);
>
>
> ---
> base-commit: 1be3b77de4eb89af8ae2fd6610546be778e25589
> change-id: 20260311-gether-disconnect-npe-5861d9831dff
>
> Best regards,
> --
> Kuen-Han Tsai <khtsai@google.com>
>
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] usb: gadget: u_ether: Fix race between gether_disconnect and eth_stop
2026-03-11 9:12 [PATCH] usb: gadget: u_ether: Fix race between gether_disconnect and eth_stop Kuen-Han Tsai
2026-03-26 7:10 ` Dayu Jiang
2026-03-26 7:16 ` Dayu Jiang
@ 2026-03-26 7:53 ` Dayu Jiang
2026-03-26 10:35 ` Greg Kroah-Hartman
2026-03-26 12:58 ` Dayu Jiang
2026-03-26 13:13 ` Dayu Jiang
4 siblings, 1 reply; 7+ messages in thread
From: Dayu Jiang @ 2026-03-26 7:53 UTC (permalink / raw)
To: Kuen-Han Tsai, Greg Kroah-Hartman
Cc: David Brownell, linux-usb, linux-kernel, stable
On Wed, Mar 11, 2026 at 05:12:15PM +0800, Kuen-Han Tsai wrote:
> A race condition between gether_disconnect() and eth_stop() leads to a
> NULL pointer dereference. Specifically, if eth_stop() is triggered
> concurrently while gether_disconnect() is tearing down the endpoints,
> eth_stop() attempts to access the cleared endpoint descriptor, causing
> the following NPE:
>
> Unable to handle kernel NULL pointer dereference
> Call trace:
> __dwc3_gadget_ep_enable+0x60/0x788
> dwc3_gadget_ep_enable+0x70/0xe4
> usb_ep_enable+0x60/0x15c
> eth_stop+0xb8/0x108
>
> Because eth_stop() crashes while holding the dev->lock, the thread
> running gether_disconnect() fails to acquire the same lock and spins
> forever, resulting in a hardlockup:
>
> Core - Debugging Information for Hardlockup core(7)
> Call trace:
> queued_spin_lock_slowpath+0x94/0x488
> _raw_spin_lock+0x64/0x6c
> gether_disconnect+0x19c/0x1e8
> ncm_set_alt+0x68/0x1a0
> composite_setup+0x6a0/0xc50
>
Hi Greg,
Hit the same issue during NCM switch stress test.
Can you take a look at this patch and check if it’s ready for merge?
Thanks,
Dayu Jiang
> The root cause is that the clearing of dev->port_usb in
> gether_disconnect() is delayed until the end of the function.
>
> Move the clearing of dev->port_usb to the very beginning of
> gether_disconnect() while holding dev->lock. This cuts off the link
> immediately, ensuring eth_stop() will see dev->port_usb as NULL and
> safely bail out.
>
> Fixes: 2b3d942c4878 ("usb ethernet gadget: split out network core")
> Cc: stable@vger.kernel.org
> Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
> ---
> drivers/usb/gadget/function/u_ether.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
> index 338f6e2a85a9..2c970a0eafd9 100644
> --- a/drivers/usb/gadget/function/u_ether.c
> +++ b/drivers/usb/gadget/function/u_ether.c
> @@ -1246,6 +1246,11 @@ void gether_disconnect(struct gether *link)
>
> DBG(dev, "%s\n", __func__);
>
> + spin_lock(&dev->lock);
> + dev->port_usb = NULL;
> + link->is_suspend = false;
> + spin_unlock(&dev->lock);
> +
> netif_stop_queue(dev->net);
> netif_carrier_off(dev->net);
>
> @@ -1283,11 +1288,6 @@ void gether_disconnect(struct gether *link)
> dev->header_len = 0;
> dev->unwrap = NULL;
> dev->wrap = NULL;
> -
> - spin_lock(&dev->lock);
> - dev->port_usb = NULL;
> - link->is_suspend = false;
> - spin_unlock(&dev->lock);
> }
> EXPORT_SYMBOL_GPL(gether_disconnect);
>
>
> ---
> base-commit: 1be3b77de4eb89af8ae2fd6610546be778e25589
> change-id: 20260311-gether-disconnect-npe-5861d9831dff
>
> Best regards,
> --
> Kuen-Han Tsai <khtsai@google.com>
>
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] usb: gadget: u_ether: Fix race between gether_disconnect and eth_stop
2026-03-26 7:53 ` Dayu Jiang
@ 2026-03-26 10:35 ` Greg Kroah-Hartman
0 siblings, 0 replies; 7+ messages in thread
From: Greg Kroah-Hartman @ 2026-03-26 10:35 UTC (permalink / raw)
To: Dayu Jiang; +Cc: Kuen-Han Tsai, David Brownell, linux-usb, linux-kernel, stable
On Thu, Mar 26, 2026 at 03:53:13PM +0800, Dayu Jiang wrote:
> On Wed, Mar 11, 2026 at 05:12:15PM +0800, Kuen-Han Tsai wrote:
> > A race condition between gether_disconnect() and eth_stop() leads to a
> > NULL pointer dereference. Specifically, if eth_stop() is triggered
> > concurrently while gether_disconnect() is tearing down the endpoints,
> > eth_stop() attempts to access the cleared endpoint descriptor, causing
> > the following NPE:
> >
> > Unable to handle kernel NULL pointer dereference
> > Call trace:
> > __dwc3_gadget_ep_enable+0x60/0x788
> > dwc3_gadget_ep_enable+0x70/0xe4
> > usb_ep_enable+0x60/0x15c
> > eth_stop+0xb8/0x108
> >
> > Because eth_stop() crashes while holding the dev->lock, the thread
> > running gether_disconnect() fails to acquire the same lock and spins
> > forever, resulting in a hardlockup:
> >
> > Core - Debugging Information for Hardlockup core(7)
> > Call trace:
> > queued_spin_lock_slowpath+0x94/0x488
> > _raw_spin_lock+0x64/0x6c
> > gether_disconnect+0x19c/0x1e8
> > ncm_set_alt+0x68/0x1a0
> > composite_setup+0x6a0/0xc50
> >
> Hi Greg,
> Hit the same issue during NCM switch stress test.
> Can you take a look at this patch and check if it’s ready for merge?
This is already in my tree and in linux-next and will go to Linus this
weekend.
thanks,
greg k-h
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] usb: gadget: u_ether: Fix race between gether_disconnect and eth_stop
2026-03-11 9:12 [PATCH] usb: gadget: u_ether: Fix race between gether_disconnect and eth_stop Kuen-Han Tsai
` (2 preceding siblings ...)
2026-03-26 7:53 ` Dayu Jiang
@ 2026-03-26 12:58 ` Dayu Jiang
2026-03-26 13:13 ` Dayu Jiang
4 siblings, 0 replies; 7+ messages in thread
From: Dayu Jiang @ 2026-03-26 12:58 UTC (permalink / raw)
To: Kuen-Han Tsai
Cc: Greg Kroah-Hartman, David Brownell, linux-usb, linux-kernel,
stable
On Wed, Mar 11, 2026 at 05:12:15PM +0800, Kuen-Han Tsai wrote:
> A race condition between gether_disconnect() and eth_stop() leads to a
> NULL pointer dereference. Specifically, if eth_stop() is triggered
> concurrently while gether_disconnect() is tearing down the endpoints,
> eth_stop() attempts to access the cleared endpoint descriptor, causing
> the following NPE:
>
> Unable to handle kernel NULL pointer dereference
> Call trace:
> __dwc3_gadget_ep_enable+0x60/0x788
> dwc3_gadget_ep_enable+0x70/0xe4
> usb_ep_enable+0x60/0x15c
> eth_stop+0xb8/0x108
>
> Because eth_stop() crashes while holding the dev->lock, the thread
> running gether_disconnect() fails to acquire the same lock and spins
> forever, resulting in a hardlockup:
>
> Core - Debugging Information for Hardlockup core(7)
> Call trace:
> queued_spin_lock_slowpath+0x94/0x488
> _raw_spin_lock+0x64/0x6c
> gether_disconnect+0x19c/0x1e8
> ncm_set_alt+0x68/0x1a0
> composite_setup+0x6a0/0xc50
>
> The root cause is that the clearing of dev->port_usb in
> gether_disconnect() is delayed until the end of the function.
>
> Move the clearing of dev->port_usb to the very beginning of
> gether_disconnect() while holding dev->lock. This cuts off the link
> immediately, ensuring eth_stop() will see dev->port_usb as NULL and
> safely bail out.
>
Hi Greg,
Hit the same issue during NCM switch stress test.
Can you take a look at this patch and check if it’s ready for merge?
Thanks,
Dayu Jiang
> Fixes: 2b3d942c4878 ("usb ethernet gadget: split out network core")
> Cc: stable@vger.kernel.org
> Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
> ---
> drivers/usb/gadget/function/u_ether.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
> index 338f6e2a85a9..2c970a0eafd9 100644
> --- a/drivers/usb/gadget/function/u_ether.c
> +++ b/drivers/usb/gadget/function/u_ether.c
> @@ -1246,6 +1246,11 @@ void gether_disconnect(struct gether *link)
>
> DBG(dev, "%s\n", __func__);
>
> + spin_lock(&dev->lock);
> + dev->port_usb = NULL;
> + link->is_suspend = false;
> + spin_unlock(&dev->lock);
> +
> netif_stop_queue(dev->net);
> netif_carrier_off(dev->net);
>
> @@ -1283,11 +1288,6 @@ void gether_disconnect(struct gether *link)
> dev->header_len = 0;
> dev->unwrap = NULL;
> dev->wrap = NULL;
> -
> - spin_lock(&dev->lock);
> - dev->port_usb = NULL;
> - link->is_suspend = false;
> - spin_unlock(&dev->lock);
> }
> EXPORT_SYMBOL_GPL(gether_disconnect);
>
>
> ---
> base-commit: 1be3b77de4eb89af8ae2fd6610546be778e25589
> change-id: 20260311-gether-disconnect-npe-5861d9831dff
>
> Best regards,
> --
> Kuen-Han Tsai <khtsai@google.com>
>
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] usb: gadget: u_ether: Fix race between gether_disconnect and eth_stop
2026-03-11 9:12 [PATCH] usb: gadget: u_ether: Fix race between gether_disconnect and eth_stop Kuen-Han Tsai
` (3 preceding siblings ...)
2026-03-26 12:58 ` Dayu Jiang
@ 2026-03-26 13:13 ` Dayu Jiang
4 siblings, 0 replies; 7+ messages in thread
From: Dayu Jiang @ 2026-03-26 13:13 UTC (permalink / raw)
To: Kuen-Han Tsai, Greg Kroah-Hartman
Cc: David Brownell, linux-usb, linux-kernel, stable
On Wed, Mar 11, 2026 at 05:12:15PM +0800, Kuen-Han Tsai wrote:
> A race condition between gether_disconnect() and eth_stop() leads to a
> NULL pointer dereference. Specifically, if eth_stop() is triggered
> concurrently while gether_disconnect() is tearing down the endpoints,
> eth_stop() attempts to access the cleared endpoint descriptor, causing
> the following NPE:
>
> Unable to handle kernel NULL pointer dereference
> Call trace:
> __dwc3_gadget_ep_enable+0x60/0x788
> dwc3_gadget_ep_enable+0x70/0xe4
> usb_ep_enable+0x60/0x15c
> eth_stop+0xb8/0x108
>
> Because eth_stop() crashes while holding the dev->lock, the thread
> running gether_disconnect() fails to acquire the same lock and spins
> forever, resulting in a hardlockup:
>
> Core - Debugging Information for Hardlockup core(7)
> Call trace:
> queued_spin_lock_slowpath+0x94/0x488
> _raw_spin_lock+0x64/0x6c
> gether_disconnect+0x19c/0x1e8
> ncm_set_alt+0x68/0x1a0
> composite_setup+0x6a0/0xc50
>
> The root cause is that the clearing of dev->port_usb in
> gether_disconnect() is delayed until the end of the function.
>
> Move the clearing of dev->port_usb to the very beginning of
> gether_disconnect() while holding dev->lock. This cuts off the link
> immediately, ensuring eth_stop() will see dev->port_usb as NULL and
> safely bail out.
>
Hi Greg,
Hit the same issue during NCM switch stress test.
Can you take a look at this patch and check if it’s ready for merge?
Thanks,
Dayu Jiang
> Fixes: 2b3d942c4878 ("usb ethernet gadget: split out network core")
> Cc: stable@vger.kernel.org
> Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
> ---
> drivers/usb/gadget/function/u_ether.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
> index 338f6e2a85a9..2c970a0eafd9 100644
> --- a/drivers/usb/gadget/function/u_ether.c
> +++ b/drivers/usb/gadget/function/u_ether.c
> @@ -1246,6 +1246,11 @@ void gether_disconnect(struct gether *link)
>
> DBG(dev, "%s\n", __func__);
>
> + spin_lock(&dev->lock);
> + dev->port_usb = NULL;
> + link->is_suspend = false;
> + spin_unlock(&dev->lock);
> +
> netif_stop_queue(dev->net);
> netif_carrier_off(dev->net);
>
> @@ -1283,11 +1288,6 @@ void gether_disconnect(struct gether *link)
> dev->header_len = 0;
> dev->unwrap = NULL;
> dev->wrap = NULL;
> -
> - spin_lock(&dev->lock);
> - dev->port_usb = NULL;
> - link->is_suspend = false;
> - spin_unlock(&dev->lock);
> }
> EXPORT_SYMBOL_GPL(gether_disconnect);
>
>
> ---
> base-commit: 1be3b77de4eb89af8ae2fd6610546be778e25589
> change-id: 20260311-gether-disconnect-npe-5861d9831dff
>
> Best regards,
> --
> Kuen-Han Tsai <khtsai@google.com>
>
^ permalink raw reply [flat|nested] 7+ messages in thread