linux-kernel - [PATCH] Avoid potential NULL deref in irq_set_irq

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Message-ID: <alpine.LNX.2.00.1106092300360.17868@swampdragon.chaosbits.net>
Date:	Thu, 9 Jun 2011 23:14:58 +0200 (CEST)
From:	Jesper Juhl <jj@...osbits.net>
To:	linux-kernel@...r.kernel.org
cc:	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] Avoid potential NULL deref in irq_set_irq_wake()

In kernel/irq/manage.c::irq_set_irq_wake() we call irq_get_desc_buslock() 
which may return NULL (it calls into 
__irq_get_desc_lock()-->irq_to_desc()-->radix_tree_lookup()-->radix_tree_lookup_element() 
which can return NULL in a number of different situations). If it does 
we'll dereference a NULL pointer - *Boom*.

irq_set_irq_wake() has lots of callers - I checked a few and I couldn't 
find anything that guarantees that they won't call it with some input that 
will cause irq_get_desc_buslock() to return NULL, so I think it's a good 
thing to test and -EINVAL was the most sane error code in this situation 
that I could think of.

Not all callers test the return value of irq_set_irq_wake(), but those 
that do take != 0 to mean error as far as I can see, so they should be 
fine. I guess those that don't test actually should, but that's a 
different issue.

Feedback welcome.

Signed-off-by: Jesper Juhl <jj@...osbits.net>
---
 manage.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

 Found by the Coverity checker.
 Untested except for build test.

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index d64bafb..b42c15c 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -488,8 +488,11 @@ static int set_irq_wake_real(unsigned int irq, unsigned int on)
 int irq_set_irq_wake(unsigned int irq, unsigned int on)
 {
 	unsigned long flags;
-	struct irq_desc *desc = irq_get_desc_buslock(irq, &flags);
 	int ret = 0;
+	struct irq_desc *desc = irq_get_desc_buslock(irq, &flags);
+
+	if (!desc)
+		return -EINVAL;

 	/* wakeup-capable irqs can be shared between drivers that
 	 * don't need to have the same sleep mode behaviors.

-- 
Jesper Juhl <jj@...osbits.net>       http://www.chaosbits.net/
Don't top-post http://www.catb.org/jargon/html/T/top-post.html
Plain text mails only, please.

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