linux-kernel - Re: [PATCH] usbnet: smsc95xx: dereferencing NULL pointer

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Date:	Mon, 10 Nov 2014 14:22:23 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	sudipm.mukherjee@...il.com
Cc:	steve.glendinning@...well.net, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usbnet: smsc95xx: dereferencing NULL pointer

From: Sudip Mukherjee <sudipm.mukherjee@...il.com>
Date: Fri,  7 Nov 2014 18:52:40 +0530

> we were dereferencing dev to initialize pdata. but just after that we
> have a BUG_ON(!dev). so we were basically dereferencing the pointer
> first and then tesing it for NULL.
> 
> Signed-off-by: Sudip Mukherjee <sudip@...torindia.org>

You didn't even compile test this.

Do not even bother fixing theoretical issues if you're going to be
introducing a _REAL_ serious regression into the code with your "fix":

drivers/net/usb/smsc95xx.c: In function ‘smsc95xx_resume’:
drivers/net/usb/smsc95xx.c:1674:5: warning: ‘pdata’ is used uninitialized in this function [-Wuninitialized]
  u8 suspend_flags = pdata->suspend_flags;
     ^

So, instead of a theoretical issue, we now have a real guaranteed
crash.

You did not compile test this change, and you definitely did not
functionally test this change either.

Please do not do this ever again, thanks.