[PATCH 6.6 031/105] usb: gadget: f_acm: Refactor bind path to use __free()

Greg Kroah-Hartman
2025-10-21T19:53:48Z

From: Kuen-Han Tsai <khtsai@google.com>

[ Upstream commit 47b2116e54b4a854600341487e8b55249e926324 ]

After an bind/unbind cycle, the acm->notify_req is left stale. If a
subsequent bind fails, the unified error label attempts to free this
stale request, leading to a NULL pointer dereference when accessing
ep->ops->free_request.

Refactor the error handling in the bind path to use the __free()
automatic cleanup mechanism.

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020
Call trace:
usb_ep_free_request+0x2c/0xec
gs_free_req+0x30/0x44
acm_bind+0x1b8/0x1f4
usb_add_function+0xcc/0x1f0
configfs_composite_bind+0x468/0x588
gadget_bind_driver+0x104/0x270
really_probe+0x190/0x374
__driver_probe_device+0xa0/0x12c
driver_probe_device+0x3c/0x218
__device_attach_driver+0x14c/0x188
bus_for_each_drv+0x10c/0x168
__device_attach+0xfc/0x198
device_initial_probe+0x14/0x24
bus_probe_device+0x94/0x11c
device_add+0x268/0x48c
usb_add_gadget+0x198/0x28c
dwc3_gadget_init+0x700/0x858
__dwc3_set_mode+0x3cc/0x664
process_scheduled_works+0x1d8/0x488
worker_thread+0x244/0x334
kthread+0x114/0x1bc
ret_from_fork+0x10/0x20

Fixes: 1f1ba11b6494 ("usb gadget: issue notifications from ACM function")
Cc: stable@kernel.org
Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
Link: https://lore.kernel.org/r/20250916-ready-v1-4-4997bf277548@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250916-ready-v1-4-4997bf277548@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/usb/gadget/function/f_acm.c | 42 ++++++++++++++++--------------------
1 file changed, 19 insertions(+), 23 deletions(-)

--- a/drivers/usb/gadget/function/f_acm.c
+++ b/drivers/usb/gadget/function/f_acm.c
@@ -11,12 +11,15 @@

/* #define VERBOSE_DEBUG */

+#include <linux/cleanup.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/err.h>

+#include <linux/usb/gadget.h>
+
#include "u_serial.h"

@@ -612,6 +615,7 @@ acm_bind(struct usb_configuration *c, st
struct usb_string *us;
int status;
struct usb_ep *ep;
+ struct usb_request *request __free(free_usb_request) = NULL;

/* REVISIT might want instance-specific strings to help
* distinguish instances ...
@@ -629,7 +633,7 @@ acm_bind(struct usb_configuration *c, st
/* allocate instance-specific interface IDs, and patch descriptors */
status = usb_interface_id(c, f);
if (status < 0)
- goto fail;
+ return status;
acm->ctrl_id = status;
acm_iad_descriptor.bFirstInterface = status;

@@ -638,40 +642,38 @@ acm_bind(struct usb_configuration *c, st

status = usb_interface_id(c, f);
if (status < 0)
- goto fail;
+ return status;
acm->data_id = status;

acm_data_interface_desc.bInterfaceNumber = status;
acm_union_desc.bSlaveInterface0 = status;
acm_call_mgmt_descriptor.bDataInterface = status;

- status = -ENODEV;
-
/* allocate instance-specific endpoints */
ep = usb_ep_autoconfig(cdev->gadget, &acm_fs_in_desc);
if (!ep)
- goto fail;
+ return -ENODEV;
acm->port.in = ep;

ep = usb_ep_autoconfig(cdev->gadget, &acm_fs_out_desc);
if (!ep)
- goto fail;
+ return -ENODEV;
acm->port.out = ep;

ep = usb_ep_autoconfig(cdev->gadget, &acm_fs_notify_desc);
if (!ep)
- goto fail;
+ return -ENODEV;
acm->notify = ep;

/* allocate notification */
- acm->notify_req = gs_alloc_req(ep,
- sizeof(struct usb_cdc_notification) + 2,
- GFP_KERNEL);
- if (!acm->notify_req)
- goto fail;
+ request = gs_alloc_req(ep,
+ sizeof(struct usb_cdc_notification) + 2,
+ GFP_KERNEL);
+ if (!request)
+ return -ENODEV;

- acm->notify_req->complete = acm_cdc_notify_complete;
- acm->notify_req->context = acm;
+ request->complete = acm_cdc_notify_complete;
+ request->context = acm;

/* support all relevant hardware speeds... we expect that when
* hardware is dual speed, all bulk-capable endpoints work at
@@ -688,7 +690,9 @@ acm_bind(struct usb_configuration *c, st
status = usb_assign_descriptors(f, acm_fs_function, acm_hs_function,
acm_ss_function, acm_ss_function);
if (status)
- goto fail;
+ return status;
+
+ acm->notify_req = no_free_ptr(request);

dev_dbg(&cdev->gadget->dev,
"acm ttyGS%d: IN/%s OUT/%s NOTIFY/%s\n",
@@ -696,14 +700,6 @@ acm_bind(struct usb_configuration *c, st
acm->port.in->name, acm->port.out->name,
acm->notify->name);
return 0;
-
-fail:
- if (acm->notify_req)
- gs_free_req(acm->notify, acm->notify_req);
-
- ERROR(cdev, "%s/%p: can't bind, err %d\n", f->name, f, status);
-
- return status;
}

static void acm_unbind(struct usb_configuration *c, struct usb_function *f)