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Date: Wed, 22 Jul 2009 17:02:26 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Jaswinder Singh Rajput <jaswinder@kernel.org>
Cc: airlied@redhat.com, catalin.marinas@arm.com, airlied@gmail.com,
       linux-kernel@vger.kernel.org, eric@anholt.net
Subject: Re: Memory leak issues in drm
Message-Id: <20090722170226.c5becf38.akpm@linux-foundation.org>
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On Thu, 16 Jul 2009 12:39:18 +0530
Jaswinder Singh Rajput <jaswinder@kernel.org> wrote:

> On Thu, 2009-07-16 at 10:37 +0530, Jaswinder Singh Rajput wrote:
> > On linus tree, while investigating kmemleak issues in drm :
> > 
> > unreferenced object 0xf571dea0 (size 32):
> >   comm "Xorg", pid 1992, jiffies 4294703188
> >   backtrace:
> >     [<c1096655>] create_object+0x140/0x210
> >     [<c10967f2>] kmemleak_alloc+0x25/0x4b
> >     [<c1093b63>] __kmalloc+0xcb/0x153
> >     [<c11ae939>] drm_setversion+0x154/0x1f6
> >     [<c11ad0b1>] drm_ioctl+0x211/0x296
> >     [<c10a2dc9>] vfs_ioctl+0x50/0x69
> >     [<c10a3321>] do_vfs_ioctl+0x49b/0x4d5
> >     [<c10a3387>] sys_ioctl+0x2c/0x45
> >     [<c1002988>] sysenter_do_call+0x12/0x36
> >     [<ffffffff>] 0xffffffff
> > 
> 
> This fixes above memory leak in drm because it was allocating again on
> dev->devname without freeing previous instance and more memory related
> issues, hope this will be helpful:
> 
> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
> index 9b9ff46..b39ab86 100644
> --- a/drivers/gpu/drm/drm_ioctl.c
> +++ b/drivers/gpu/drm/drm_ioctl.c
> @@ -96,25 +96,36 @@ int drm_setunique(struct drm_device *dev, void *data,

drm_setunique() is pretty crappy.  It has a number of places where it
does some resource freeing and then a `return' and other places where
it does the usual `goto out_free' thing.

I do think that converting this function to the usual
single-return-statement model would simplify it and would reduce the
chances of additional resource leaks being added in the future.

The basic pattern (which is applicable here) is:

foo()
{
	if (!simple test)
		return -EFOO;
	if (!simple_test_2)
		return -EBAR;

	foo = allocate_something();

	if (test3)
		goto fail_foo;

	bar = allocate_something_else();

	if (test4)
		goto fail_bar;

	...

	return 0;		/* success */

fail_bar:
	deallocate(bar);
fail_foo:
	deallocate(foo);

	return err;
}

>  	master->unique = kmalloc(master->unique_size, GFP_KERNEL);
>  	if (!master->unique)
>  		return -ENOMEM;
> -	if (copy_from_user(master->unique, u->unique, master->unique_len))
> +	if (copy_from_user(master->unique, u->unique, master->unique_len)) {
> +		kfree(master->unique);
> +		master->unique_len = 0;
>  		return -EFAULT;
> +	}
>  
>  	master->unique[master->unique_len] = '\0';
>  
> +	/* Free previous dev->devname, if exists */
> +	if (dev->devname)
> +		kfree(dev->devname);

kfree(NULL) is legal and will simplify and shorten the code here.

>  	dev->devname = kmalloc(strlen(dev->driver->pci_driver.name) +
>  			       strlen(master->unique) + 2, GFP_KERNEL);
> -	if (!dev->devname)
> +	if (!dev->devname) {
> +		kfree(master->unique);
> +		master->unique_len = 0;
>  		return -ENOMEM;
> +	}
>  
>  	sprintf(dev->devname, "%s@%s", dev->driver->pci_driver.name,
>  		master->unique);
>  
> -	/* Return error if the busid submitted doesn't match the device's actual
> +	/*
> +	 * Return error if the busid submitted doesn't match the device's actual
>  	 * busid.
>  	 */
>  	ret = sscanf(master->unique, "PCI:%d:%d:%d", &bus, &slot, &func);
>  	if (ret != 3)
> -		return -EINVAL;
> +		goto error;
> +
>  	domain = bus >> 8;
>  	bus &= 0xff;
>  
> @@ -122,9 +133,15 @@ int drm_setunique(struct drm_device *dev, void *data,
>  	    (bus != dev->pdev->bus->number) ||
>  	    (slot != PCI_SLOT(dev->pdev->devfn)) ||
>  	    (func != PCI_FUNC(dev->pdev->devfn)))
> -		return -EINVAL;
> +		goto error;
>  
>  	return 0;
> +
> +error:
> +	kfree(dev->devname);
> +	kfree(master->unique);
> +
> +	return -EINVAL;
>  }
>  
>  static int drm_set_busid(struct drm_device *dev, struct drm_file *file_priv)
> @@ -136,25 +153,35 @@ static int drm_set_busid(struct drm_device *dev, struct drm_file *file_priv)
>  		return -EBUSY;
>  
>  	master->unique_len = 40;
> -	master->unique_size = master->unique_len;
> +	master->unique_size = master->unique_len + 1;
>  	master->unique = kmalloc(master->unique_size, GFP_KERNEL);
>  	if (master->unique == NULL)
>  		return -ENOMEM;
>  
> -	len = snprintf(master->unique, master->unique_len, "pci:%04x:%02x:%02x.%d",
> +	/*
> +	 * Using sprintf as it will return number of characters
> +	 * (not including the trailing '\0')
> +	 */
> +	len = sprintf(master->unique, "pci:%04x:%02x:%02x.%d",
>  		       drm_get_pci_domain(dev),
>  		       dev->pdev->bus->number,
>  		       PCI_SLOT(dev->pdev->devfn),
>  		       PCI_FUNC(dev->pdev->devfn));
> -	if (len >= master->unique_len)
> +	if (len > master->unique_len)
>  		DRM_ERROR("buffer overflow");
>  	else
>  		master->unique_len = len;
>  
> +	/* Free previous dev->devname, if exists */
> +	if (dev->devname)
> +		kfree(dev->devname);

and here.

>  	dev->devname = kmalloc(strlen(dev->driver->pci_driver.name) +
>  			       master->unique_len + 2, GFP_KERNEL);
> -	if (dev->devname == NULL)
> +	if (dev->devname == NULL) {
> +		kfree(master->unique);
> +		master->unique_len = 0;
>  		return -ENOMEM;
> +	}
>  
>  	sprintf(dev->devname, "%s@%s", dev->driver->pci_driver.name,
>  		master->unique);
> 
--
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