linux-kernel - [PATCH] rtc: s5m: Remove VLA usage

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Message-ID: <20180308172031.GA14541@embeddedgus>
Date:   Thu, 8 Mar 2018 11:20:31 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Sangbeom Kim <sbkim73@...sung.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-rtc@...r.kernel.org, kernel-hardening@...ts.openwall.com,
        Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>
Subject: [PATCH] rtc: s5m: Remove VLA usage

In preparation to enabling -Wvla, remove VLAs and replace them
with fixed-length arrays instead.

>From a security viewpoint, the use of Variable Length Arrays can be
a vector for stack overflow attacks. Also, in general, as the code
evolves it is easy to lose track of how big a VLA can get. Thus, we
can end up having segfaults that are hard to debug.

Also, fixed as part of the directive to remove all VLAs from
the kernel: https://lkml.org/lkml/2018/3/7/621

Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
 drivers/rtc/rtc-s5m.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/rtc/rtc-s5m.c b/drivers/rtc/rtc-s5m.c
index 6deae10..2b5f4f7 100644
--- a/drivers/rtc/rtc-s5m.c
+++ b/drivers/rtc/rtc-s5m.c
@@ -38,6 +38,9 @@
  */
 #define UDR_READ_RETRY_CNT	5
 
+/* Maximum number of registers for setting time/alarm0/alarm1 */
+#define MAX_NUM_TIME_REGS	8
+
 /*
  * Registers used by the driver which are different between chipsets.
  *
@@ -367,7 +370,7 @@ static void s5m8763_tm_to_data(struct rtc_time *tm, u8 *data)
 static int s5m_rtc_read_time(struct device *dev, struct rtc_time *tm)
 {
 	struct s5m_rtc_info *info = dev_get_drvdata(dev);
-	u8 data[info->regs->regs_count];
+	u8 data[MAX_NUM_TIME_REGS];
 	int ret;
 
 	if (info->regs->read_time_udr_mask) {
@@ -413,7 +416,7 @@ static int s5m_rtc_read_time(struct device *dev, struct rtc_time *tm)
 static int s5m_rtc_set_time(struct device *dev, struct rtc_time *tm)
 {
 	struct s5m_rtc_info *info = dev_get_drvdata(dev);
-	u8 data[info->regs->regs_count];
+	u8 data[MAX_NUM_TIME_REGS];
 	int ret = 0;
 
 	switch (info->device_type) {
@@ -450,7 +453,7 @@ static int s5m_rtc_set_time(struct device *dev, struct rtc_time *tm)
 static int s5m_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
 {
 	struct s5m_rtc_info *info = dev_get_drvdata(dev);
-	u8 data[info->regs->regs_count];
+	u8 data[MAX_NUM_TIME_REGS];
 	unsigned int val;
 	int ret, i;
 
@@ -500,7 +503,7 @@ static int s5m_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
 
 static int s5m_rtc_stop_alarm(struct s5m_rtc_info *info)
 {
-	u8 data[info->regs->regs_count];
+	u8 data[MAX_NUM_TIME_REGS];
 	int ret, i;
 	struct rtc_time tm;
 
@@ -545,7 +548,7 @@ static int s5m_rtc_stop_alarm(struct s5m_rtc_info *info)
 static int s5m_rtc_start_alarm(struct s5m_rtc_info *info)
 {
 	int ret;
-	u8 data[info->regs->regs_count];
+	u8 data[MAX_NUM_TIME_REGS];
 	u8 alarm0_conf;
 	struct rtc_time tm;
 
@@ -598,7 +601,7 @@ static int s5m_rtc_start_alarm(struct s5m_rtc_info *info)
 static int s5m_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
 {
 	struct s5m_rtc_info *info = dev_get_drvdata(dev);
-	u8 data[info->regs->regs_count];
+	u8 data[MAX_NUM_TIME_REGS];
 	int ret;
 
 	switch (info->device_type) {
-- 
2.7.4