[PATCH v3] usb: core: fix quirks_param_set() writing to a const pointer

["Kars Mulder" <kerneldev@karsmulder.nl>]

The function quirks_param_set() takes as argument a const char* pointer
to the new value of the usbcore.quirks parameter. It then casts this
pointer to a non-const char* pointer and passes it to the strsep()
function, which overwrites the value.

Fix this by creating a copy of the value using kstrdup() and letting
that copy be written to by strsep().

Fixes: 027bd6cafd9a ("usb: core: Add "quirks" parameter for usbcore")
Signed-off-by: Kars Mulder <kerneldev@karsmulder.nl>

---

Changes v1 -> v2:
  * Uses a different approach; now copies the value to the heap using
    kstrdup() rather than copying it to a buffer on the stack.

Changes v2 -> v3:
  * Added a changelog between patch versions.


 drivers/usb/core/quirks.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/core/quirks.c b/drivers/usb/core/quirks.c
index e0b77674869c..c96c50faccf7 100644
--- a/drivers/usb/core/quirks.c
+++ b/drivers/usb/core/quirks.c
@@ -25,17 +25,23 @@ static unsigned int quirk_count;
 
 static char quirks_param[128];
 
-static int quirks_param_set(const char *val, const struct kernel_param *kp)
+static int quirks_param_set(const char *value, const struct kernel_param *kp)
 {
-	char *p, *field;
+	char *val, *p, *field;
 	u16 vid, pid;
 	u32 flags;
 	size_t i;
 	int err;
 
+	val = kstrdup(value, GFP_KERNEL);
+	if (!val)
+		return -ENOMEM;
+
 	err = param_set_copystring(val, kp);
-	if (err)
+	if (err) {
+		kfree(val);
 		return err;
+	}
 
 	mutex_lock(&quirk_mutex);
 
@@ -60,10 +66,11 @@ static int quirks_param_set(const char *val, const struct kernel_param *kp)
 	if (!quirk_list) {
 		quirk_count = 0;
 		mutex_unlock(&quirk_mutex);
+		kfree(val);
 		return -ENOMEM;
 	}
 
-	for (i = 0, p = (char *)val; p && *p;) {
+	for (i = 0, p = val; p && *p;) {
 		/* Each entry consists of VID:PID:flags */
 		field = strsep(&p, ":");
 		if (!field)
@@ -144,6 +151,7 @@ static int quirks_param_set(const char *val, const struct kernel_param *kp)
 
 unlock:
 	mutex_unlock(&quirk_mutex);
+	kfree(val);
 
 	return 0;
 }
-- 
2.27.0