linux-kernel - Re: Null dereference errors in the kernel

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Date:	Tue, 18 Jul 2006 10:24:29 +0100
From:	Daniel Drake <dsd@...too.org>
To:	Thomas Dillig <tdillig@...nford.edu>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Null dereference errors in the kernel

Thomas Dillig wrote:
> Hello,
> 
> We are PhD students at Stanford University working on a static analysis 
> project called SATURN (http://glide.stanford.edu/saturn). We have 
> implemented a checker that finds potential null dereference errors and 
> ran our tool on the kernel version 2.6.17.1. We have identified around 
> 300 potential issues related to null errors, and we've included 20 
> sample reports below. If you would be interested, we can post all the 
> issues we found. Also, we apologize in advance if we aren't supposed to 
> post these error reports here, and we are happy to submit bug reports 
> elsewhere if you tell us where to post these.

Interesting idea. I just looked at one of them out of curiosity, but I'm 
not sure it is valid. Either that or I have misunderstood the problem it 
is identifying?

> [13]
> 1176, 1180 drivers/char/isicom.c
> Possible null dereference of variable "tty" checked for NULL at 
> (1183:drivers/char/isicom.c).

This function is part of the tty_operations API, that would be a pretty 
broken interface if it provided the possibility of a NULL tty to work 
on. Additionally, all of the callers seem to do this:

	tty->driver->put_char(tty, c);

If tty is NULL here, we have larger problems at hand :)

I'm also unsure how this null dereference is related to line 1183.

Daniel
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