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Subject[PATCH v2] rtc: remove VLA usage
In preparation to enabling -Wvla, remove VLA and replace it
with a fixed-length array 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 <garsilva@embeddedor.com>
---
Changes in v2:
- Update changelog as per Alexandre Belloni request.
- Update the code for rtc-bq32k driver based on Alexandre's feedback.

drivers/rtc/rtc-bq32k.c | 6 +++++-
drivers/rtc/rtc-mcp795.c | 2 +-
2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/rtc/rtc-bq32k.c b/drivers/rtc/rtc-bq32k.c
index e8698e9..ef52741 100644
--- a/drivers/rtc/rtc-bq32k.c
+++ b/drivers/rtc/rtc-bq32k.c
@@ -36,6 +36,10 @@
#define BQ32K_CFG2 0x09 /* Trickle charger control */
#define BQ32K_TCFE BIT(6) /* Trickle charge FET bypass */

+#define MAX_LEN 10 /* Maximum number of consecutive
+ * register for this particular RTC.
+ */
+
struct bq32k_regs {
uint8_t seconds;
uint8_t minutes;
@@ -74,7 +78,7 @@ static int bq32k_read(struct device *dev, void *data, uint8_t off, uint8_t len)
static int bq32k_write(struct device *dev, void *data, uint8_t off, uint8_t len)
{
struct i2c_client *client = to_i2c_client(dev);
- uint8_t buffer[len + 1];
+ uint8_t buffer[MAX_LEN + 1];

buffer[0] = off;
memcpy(&buffer[1], data, len);
diff --git a/drivers/rtc/rtc-mcp795.c b/drivers/rtc/rtc-mcp795.c
index 79e24ea..00e11c1 100644
--- a/drivers/rtc/rtc-mcp795.c
+++ b/drivers/rtc/rtc-mcp795.c
@@ -82,7 +82,7 @@ static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
{
struct spi_device *spi = to_spi_device(dev);
int ret;
- u8 tx[2 + count];
+ u8 tx[257];

tx[0] = MCP795_WRITE;
tx[1] = addr;
--
2.7.4
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