linux-kernel - [PATCH] Fix array overflow in CFQ

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Message-Id: <1287479450-11447-1-git-send-email-andi@firstfloor.org>
Date:	Tue, 19 Oct 2010 11:10:50 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	axboe@...nel.dk
Cc:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH] Fix array overflow in CFQ

From: Andi Kleen <ak@...ux.intel.com>

gcc 4.5 complains when compiling a recent rc with

linux/block/cfq-iosched.c: In function ‘cfq_dispatch_requests’:
linux/block/cfq-iosched.c:2156:3: warning: array subscript is above array bounds

and it is right:

 slice = group_slice * count /
                max_t(unsigned, cfqg->busy_queues_avg[cfqd->serving_prio],
                      cfq_group_busy_queues_wl(cfqd->serving_prio, cfqd, cfqg));

busy_queues_avg can be indexed by this enum

enum wl_prio_t {
        BE_WORKLOAD = 0,
        RT_WORKLOAD = 1,
        IDLE_WORKLOAD = 2,
};

in cfqd->serving_prio, but is only declared as

unsigned int busy_queues_avg[2];

which is clearly off by one. Fix this here.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 block/cfq-iosched.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 9eba291..76741da 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -185,7 +185,7 @@ struct cfq_group {
 	int nr_cfqq;
 
 	/* Per group busy queus average. Useful for workload slice calc. */
-	unsigned int busy_queues_avg[2];
+	unsigned int busy_queues_avg[3];
 	/*
 	 * rr lists of queues with requests, onle rr for each priority class.
 	 * Counts are embedded in the cfq_rb_root
-- 
1.7.1

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