[PATCH] usbnet: smsc95xx: dereferencing NULL pointer

[PATCH] usbnet: smsc95xx: dereferencing NULL pointer

[Sudip Mukherjee]

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@vectorindia.org>
---
 drivers/net/usb/smsc95xx.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/smsc95xx.c b/drivers/net/usb/smsc95xx.c
index d07bf4c..3393238 100644
--- a/drivers/net/usb/smsc95xx.c
+++ b/drivers/net/usb/smsc95xx.c
@@ -1670,12 +1670,13 @@ done:
 static int smsc95xx_resume(struct usb_interface *intf)
 {
 	struct usbnet *dev = usb_get_intfdata(intf);
-	struct smsc95xx_priv *pdata = (struct smsc95xx_priv *)(dev->data[0]);
+	struct smsc95xx_priv *pdata;
 	u8 suspend_flags = pdata->suspend_flags;
 	int ret;
 	u32 val;
 
 	BUG_ON(!dev);
+	pdata = (struct smsc95xx_priv *)(dev->data[0]);
 
 	netdev_dbg(dev->net, "resume suspend_flags=0x%02x\n", suspend_flags);
 
-- 
1.8.1.2

Re: [PATCH] usbnet: smsc95xx: dereferencing NULL pointer

[David Miller]

From: Sudip Mukherjee <sudipm.mukherjee@gmail.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@vectorindia.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.

Re: [PATCH] usbnet: smsc95xx: dereferencing NULL pointer

[Sudip Mukherjee]

On Mon, Nov 10, 2014 at 02:22:23PM -0500, David Miller wrote:
> From: Sudip Mukherjee <sudipm.mukherjee@gmail.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@vectorindia.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.

extremely sorry for this.
i have compile tested but don't know how i missed the new warning message.
for any of my patch,if for some reason i am not able to compile test it, i mention that in the comments.
sorry again.

thanks
sudip