[tip:irq/core] irqdomain: Prevent potential NULL pointer dereference in irq_domain_push_irq()

[tip-bot for Dan Carpenter <tipbot@zytor.com>]

Commit-ID:  20c4d49c0f304f3f945bbd560b26afa98f75a0c4
Gitweb:     http://git.kernel.org/tip/20c4d49c0f304f3f945bbd560b26afa98f75a0c4
Author:     Dan Carpenter <dan.carpenter@oracle.com>
AuthorDate: Fri, 25 Aug 2017 15:14:09 +0300
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 25 Aug 2017 22:40:26 +0200

irqdomain: Prevent potential NULL pointer dereference in irq_domain_push_irq()

This code generates a Smatch warning:

  kernel/irq/irqdomain.c:1511 irq_domain_push_irq()
  warn: variable dereferenced before check 'root_irq_data' (see line 1508)

irq_get_irq_data() can return a NULL pointer, but the code dereferences
the returned pointer before checking it.

Move the NULL pointer check before the dereference.

[ tglx: Rewrote changelog to be precise and conforming to the instructions
  	in submitting-patches and added a Fixes tag. Sigh! ]

Fixes: 495c38d3001f ("irqdomain: Add irq_domain_{push,pop}_irq() functions")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: David Daney <david.daney@cavium.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: kernel-janitors@vger.kernel.org
Link: http://lkml.kernel.org/r/20170825121409.6rfv4vt6ztz2oqkt@mwanda

---
 kernel/irq/irqdomain.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
index 1ff9912..d623517 100644
--- a/kernel/irq/irqdomain.c
+++ b/kernel/irq/irqdomain.c
@@ -1504,10 +1504,10 @@ int irq_domain_push_irq(struct irq_domain *domain, int virq, void *arg)
 	if (WARN_ON(!irq_domain_is_hierarchy(domain)))
 		return -EINVAL;
 
-	if (domain->parent != root_irq_data->domain)
+	if (!root_irq_data)
 		return -EINVAL;
 
-	if (!root_irq_data)
+	if (domain->parent != root_irq_data->domain)
 		return -EINVAL;
 
 	child_irq_data = kzalloc_node(sizeof(*child_irq_data), GFP_KERNEL,