[PATCH] memory: gpmc: fix out of bounds read and dereference on gpmc_cs[]

From: Colin King <colin.king@canonical.com>
To: Roger Quadros <rogerq@kernel.org>,
	Tony Lindgren <tony@atomide.com>,
	Krzysztof Kozlowski <krzk@kernel.org>,
	linux-omap@vger.kernel.org
Cc: kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] memory: gpmc: fix out of bounds read and dereference on gpmc_cs[]
Date: Tue, 23 Feb 2021 19:38:21 +0000	[thread overview]
Message-ID: <20210223193821.17232-1-colin.king@canonical.com> (raw)

From: Colin Ian King <colin.king@canonical.com>

Currently the array gpmc_cs is indexed by cs before it cs is range checked
and the pointer read from this out-of-index read is dereferenced. Fix this
by performing the range check on cs before the read and the following
pointer dereference.

Addresses-Coverity: ("Negative array index read")
Fixes: 186401937927 ("memory: gpmc: Move omap gpmc code to live under drivers")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 drivers/memory/omap-gpmc.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/memory/omap-gpmc.c b/drivers/memory/omap-gpmc.c
index cfa730cfd145..f80c2ea39ca4 100644
--- a/drivers/memory/omap-gpmc.c
+++ b/drivers/memory/omap-gpmc.c
@@ -1009,8 +1009,8 @@ EXPORT_SYMBOL(gpmc_cs_request);
 
 void gpmc_cs_free(int cs)
 {
-	struct gpmc_cs_data *gpmc = &gpmc_cs[cs];
-	struct resource *res = &gpmc->mem;
+	struct gpmc_cs_data *gpmc;
+	struct resource *res;
 
 	spin_lock(&gpmc_mem_lock);
 	if (cs >= gpmc_cs_num || cs < 0 || !gpmc_cs_reserved(cs)) {
@@ -1018,6 +1018,9 @@ void gpmc_cs_free(int cs)
 		spin_unlock(&gpmc_mem_lock);
 		return;
 	}
+	gpmc = &gpmc_cs[cs];
+	res = &gpmc->mem;
+
 	gpmc_cs_disable_mem(cs);
 	if (res->flags)
 		release_resource(res);
-- 
2.30.0

