Re: [patch] gpio: potential null dereference

[Daniel Glöckner]

On Mon, Apr 26, 2010 at 09:25:20PM +0200, Dan Carpenter wrote:
> Smatch found a potential null dereference in gpio_setup_irq().  The 
> "pdesc" variable is allocated with idr_find() that can return NULL.  If
> gpio_setup_irq() is called with 0 as gpio_flags and "pdesc" is null, it
> would OOPs here.

idr_find() doesn't allocate, idr_get_new_above() does.
Assuming idr_find() never fails for an id if idr_get_new_above()
successfully allocated that id, I don't think we can reach that
line with pdesc being NULL:

- There are two gotos leading to free_sd
- #2 is after a block that allocates pdesc
- #1 is in an if (!gpio_flags) block
- We exit early if ((desc->flags & GPIO_TRIGGER_MASK) == gpio_flags)
- Therefore (desc->flags & GPIO_TRIGGER_MASK) must be != 0 to reach #1
- Trigger flags are added to desc->flags only after we have
  successfully allocated pdesc (i.e. right before return 0)
- We start off with no trigger flags set

  Daniel


-- 
Dipl.-Math. Daniel Glöckner, emlix GmbH, http://www.emlix.com
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