linux-kernel - Re: [PATCH] mm: dmapool: fix possible use after free in dmam_pool

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Message-ID: <20110602142242.GA4115@maxin>
Date:	Thu, 2 Jun 2011 17:22:42 +0300
From:	Maxin B John <maxin.john@...il.com>
To:	eike-kernel@...tec.de
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, dima@...roid.com, willy@...ux.intel.com,
	segooon@...il.com, tj@...nel.org, jkosina@...e.cz,
	tglx@...utronix.de
Subject: Re: [PATCH] mm: dmapool: fix possible use after free in
 dmam_pool_destroy()

On Thu, Jun 2, 2011 at 12:47 PM, Rolf Eike Beer <eike-kernel@...tec.de> wrote:
> Maxin B John wrote:
>> "dma_pool_destroy(pool)" calls "kfree(pool)". The freed pointer
>> "pool" is again passed as an argument to the function "devres_destroy()".
>> This patch fixes the possible use after free.
>
> The pool itself is not used there, only the address where the pool
> has been.This will only lead to any trouble if something else is allocated to
> the same place and inserted into the devres list of the same device between
> the dma_pool_destroy() and devres_destroy().

Thank you very much for explaining it in detail. 

> But I agree that this is bad style. But if you are going to change
> this please also have a look at devm_iounmap() in lib/devres.c. Maybe also the
> devm_*irq* functions need the same changes.

As per your suggestion, I have made similar modifications for lib/devres.c and
kernel/irq/devres.c

CCed the maintainers of the respective files.
 
Signed-off-by: Maxin B. John <maxin.john@...il.com>
---
diff --git a/kernel/irq/devres.c b/kernel/irq/devres.c
index 1ef4ffc..bd8e788 100644
--- a/kernel/irq/devres.c
+++ b/kernel/irq/devres.c
@@ -87,8 +87,8 @@ void devm_free_irq(struct device *dev, unsigned int irq, void *dev_id)
 {
 	struct irq_devres match_data = { irq, dev_id };
 
-	free_irq(irq, dev_id);
 	WARN_ON(devres_destroy(dev, devm_irq_release, devm_irq_match,
 			       &match_data));
+	free_irq(irq, dev_id);
 }
 EXPORT_SYMBOL(devm_free_irq);
diff --git a/lib/devres.c b/lib/devres.c
index 6efddf5..7c0e953 100644
--- a/lib/devres.c
+++ b/lib/devres.c
@@ -79,9 +79,9 @@ EXPORT_SYMBOL(devm_ioremap_nocache);
  */
 void devm_iounmap(struct device *dev, void __iomem *addr)
 {
-	iounmap(addr);
 	WARN_ON(devres_destroy(dev, devm_ioremap_release, devm_ioremap_match,
 			       (void *)addr));
+	iounmap(addr);
 }
 EXPORT_SYMBOL(devm_iounmap);
 
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