usb: gadget: function: fix dangling pnp_string in f_printer.c

When opts->pnp_string is changed with configfs, new memory is allocated for
the string. It does not, however, update dev->pnp_string, even though the
memory is freed. When rquesting the string, the host then gets old or
corrupted data rather than the new string. The ieee 1284 id string should
be allowed to change while the device is connected.

The bug was introduced in commit fdc01cc286be ("usb: gadget: printer:
Remove pnp_string static buffer"), which changed opts->pnp_string from a
char[] to a char*.
This patch changes dev->pnp_string from a char* to a char** pointing to
opts->pnp_string.

Fixes: fdc01cc286be ("usb: gadget: printer: Remove pnp_string static buffer")
Signed-off-by: Albert Briscoe <albertsbriscoe@gmail.com>
Link: https://lore.kernel.org/r/20220911223753.20417-1-albertsbriscoe@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget/function/f_printer.c
index abec5c58f5251ae3e7c3a34a8521b1b9465ea86e..a881c69b1f2bf56cf20fda287efcd708e7abdbe3 100644 (file)
--- a/drivers/usb/gadget/function/f_printer.c
+++ b/drivers/usb/gadget/function/f_printer.c
@@ -89,7 +89,7 @@ struct printer_dev {
        u8                      printer_cdev_open;
        wait_queue_head_t       wait;
        unsigned                q_len;
-       char                    *pnp_string;    /* We don't own memory! */
+       char                    **pnp_string;   /* We don't own memory! */
        struct usb_function     function;
 };
 
@@ -1000,16 +1000,16 @@ static int printer_func_setup(struct usb_function *f,
                        if ((wIndex>>8) != dev->interface)
                                break;
 
-                       if (!dev->pnp_string) {
+                       if (!*dev->pnp_string) {
                                value = 0;
                                break;
                        }
-                       value = strlen(dev->pnp_string);
+                       value = strlen(*dev->pnp_string);
                        buf[0] = (value >> 8) & 0xFF;
                        buf[1] = value & 0xFF;
-                       memcpy(buf + 2, dev->pnp_string, value);
+                       memcpy(buf + 2, *dev->pnp_string, value);
                        DBG(dev, "1284 PNP String: %x %s\n", value,
-                           dev->pnp_string);
+                           *dev->pnp_string);
                        break;
 
                case GET_PORT_STATUS: /* Get Port Status */
@@ -1475,7 +1475,7 @@ static struct usb_function *gprinter_alloc(struct usb_function_instance *fi)
        kref_init(&dev->kref);
        ++opts->refcnt;
        dev->minor = opts->minor;
-       dev->pnp_string = opts->pnp_string;
+       dev->pnp_string = &opts->pnp_string;
        dev->q_len = opts->q_len;
        mutex_unlock(&opts->lock);