Re: [PATCH 2/2] USB: core: Fix potential memory leak in usb_get_configuration()

[Tiezhu Yang]

On 02/26/2020 04:09 PM, Johan Hovold wrote:
> On Wed, Feb 26, 2020 at 02:15:23PM +0800, Tiezhu Yang wrote:
> > Make sure to free all the allocated memory before exiting from the function
> > usb_get_configuration() when an error is encountered.
> There's no leak in this function as far as I can tell. Any allocated
> memory is released in usb_destroy_configuration() when the last
> reference to the struct usb_device is dropped.

Yes, you are right, the allocated memory in usb_get_configuration()
will be released in usb_destroy_configuration().

By the way, is it better to release the allocated memory as early as 
possible
in usb_get_configuration()? Just like this:

diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index bb63ee0..dd4ebeb 100644
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -885,12 +885,17 @@ int usb_get_configuration(struct usb_device *dev)

        length = ncfg * sizeof(char *);
        dev->rawdescriptors = kzalloc(length, GFP_KERNEL);
-       if (!dev->rawdescriptors)
+       if (!dev->rawdescriptors) {
+               kfree(dev->config);
                return -ENOMEM;
+       }

        desc = kmalloc(USB_DT_CONFIG_SIZE, GFP_KERNEL);
-       if (!desc)
+       if (!desc) {
+               kfree(dev->config);
+               kfree(dev->rawdescriptors);
                return -ENOMEM;
+       }

        for (cfgno = 0; cfgno < ncfg; cfgno++) {
                /* We grab just the first descriptor so we know how long

Thanks,

Tiezhu Yang

> > Additionally, just initialize the variable "bigbuffer" with NULL to avoid
> > the following build warning:
> >
> >    CC      drivers/usb/core/config.o
> > drivers/usb/core/config.c: In function âusb_get_configurationâ:
> > drivers/usb/core/config.c:956:2: warning: âbigbufferâ may be used uninitialized in this function [-Wmaybe-uninitialized]
> >    kfree(bigbuffer);
> >    ^
> No need to mention warnings that you introduce yourself while creating
> your patch. It can give the false impression that your addressing an
> existing issue.
>
> Johan