linux-kernel - Re: [PATCH 2/2] USB: core: Fix potential memory leak in usb_get

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Date:   Wed, 26 Feb 2020 16:42:55 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Johan Hovold <johan@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xuefeng Li <lixuefeng@...ngson.cn>
Subject: Re: [PATCH 2/2] USB: core: Fix potential memory leak in
 usb_get_configuration()

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 ‘usb_get_configuration’:
>> drivers/usb/core/config.c:956:2: warning: ‘bigbuffer’ 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