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Message-ID: <23757731-bfa5-cb4c-ddc0-04103f9a72e0@embeddedor.com>
Date: Thu, 8 Mar 2018 12:03:29 -0600
From: "Gustavo A. R. Silva" <garsilva@...eddedor.com>
To: Kees Cook <keescook@...omium.org>,
"Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc: 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>,
LKML <linux-kernel@...r.kernel.org>, linux-samsung-soc@...r.kernel.org,
linux-rtc@...r.kernel.org,
Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH] rtc: s5m: Remove VLA usage
On 03/08/2018 11:58 AM, Kees Cook wrote:
> On Thu, Mar 8, 2018 at 9:20 AM, Gustavo A. R. Silva
> <gustavo@...eddedor.com> wrote:
>> 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
>
> I would adjust the various const struct s5m_rtc_reg_config's
> .regs_count to be represented by this new define, so the stack and the
> structures stay in sync. Something like:
>
> static const struct s5m_rtc_reg_config s2mps13_rtc_regs = {
> .regs_count = MAX_NUM_TIME_REGS - 1,
>
> ?
>
Yep. I thought about that and decided to wait for some feedback first.
But yeah, I think is that'd be a good change.
--
Gustavo
> -Kees
>
>> +
>> /*
>> * 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
>>
>
>
>
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