[PATCH 6.18 149/333] usb: legacy: ncm: Fix NPE in gncm_bind

Greg Kroah-Hartman
2026-03-17T17:15:46Z

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

commit fde0634ad9856b3943a2d1a8cc8de174a63ac840 upstream.

Commit 56a512a9b410 ("usb: gadget: f_ncm: align net_device lifecycle
with bind/unbind") deferred the allocation of the net_device. This
change leads to a NULL pointer dereference in the legacy NCM driver as
it attempts to access the net_device before it's fully instantiated.

Store the provided qmult, host_addr, and dev_addr into the struct
ncm_opts->net_opts during gncm_bind(). These values will be properly
applied to the net_device when it is allocated and configured later in
the binding process by the NCM function driver.

Fixes: 56a512a9b410 ("usb: gadget: f_ncm: align net_device lifecycle with bind/unbind")
Cc: stable@kernel.org
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202602181727.fd76c561-lkp@intel.com
Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
Link: https://patch.msgid.link/20260221-legacy-ncm-v2-1-dfb891d76507@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/usb/gadget/legacy/ncm.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/gadget/legacy/ncm.c b/drivers/usb/gadget/legacy/ncm.c
index 0f1b45e3abd1..e8d565534053 100644
--- a/drivers/usb/gadget/legacy/ncm.c
+++ b/drivers/usb/gadget/legacy/ncm.c
@@ -15,8 +15,10 @@
/* #define DEBUG */
/* #define VERBOSE_DEBUG */

+#include <linux/hex.h>
#include <linux/kernel.h>
#include <linux/module.h>
+#include <linux/string.h>
#include <linux/usb/composite.h>

#include "u_ether.h"
@@ -129,6 +131,7 @@ static int gncm_bind(struct usb_composite_dev *cdev)
struct usb_gadget *gadget = cdev->gadget;
struct f_ncm_opts *ncm_opts;
int status;
+ u8 mac[ETH_ALEN];

f_ncm_inst = usb_get_function_instance("ncm");
if (IS_ERR(f_ncm_inst))
@@ -136,11 +139,15 @@ static int gncm_bind(struct usb_composite_dev *cdev)

ncm_opts = container_of(f_ncm_inst, struct f_ncm_opts, func_inst);

- gether_set_qmult(ncm_opts->net, qmult);
- if (!gether_set_host_addr(ncm_opts->net, host_addr))
+ ncm_opts->net_opts.qmult = qmult;
+ if (host_addr && mac_pton(host_addr, mac)) {
+ memcpy(&ncm_opts->net_opts.host_mac, mac, ETH_ALEN);
pr_info("using host ethernet address: %s", host_addr);
- if (!gether_set_dev_addr(ncm_opts->net, dev_addr))
+ }
+ if (dev_addr && mac_pton(dev_addr, mac)) {
+ memcpy(&ncm_opts->net_opts.dev_mac, mac, ETH_ALEN);
pr_info("using self ethernet address: %s", dev_addr);
+ }

/* Allocate string descriptor numbers ... note that string
* contents can be overridden by the composite_dev glue.
--
2.53.0