Messages in this thread | | | Subject | Re: [PATCH] rtc: s5m: Remove VLA usage | From | "Gustavo A. R. Silva" <> | Date | Fri, 9 Mar 2018 22:34:55 -0600 |
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Hi Krzysztof,
On 03/09/2018 07:04 AM, Krzysztof Kozlowski wrote: > On Thu, Mar 8, 2018 at 7:03 PM, Gustavo A. R. Silva > <garsilva@embeddedor.com> wrote: >> >> >> On 03/08/2018 11:58 AM, Kees Cook wrote: >>> >>> On Thu, Mar 8, 2018 at 9:20 AM, Gustavo A. R. Silva >>> <gustavo@embeddedor.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@embeddedor.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. > > Define and these assignments should be somehow connected with enum > defining the offsets for data[] (from > include/linux/mfd/samsung/rtc.h). Otherwise we define the same in two > places. The enum could be itself (in separate patch) moved to the > driver because it is meaningless for others. >
I got it.
I'll move the enum to rtc-s5m.c and add RTC_MAX_NUM_TIME_REGS at the end of it. I'll send a patch series for this.
Thanks for the feedback. -- Gustavo
> Best regards, > Krzysztof >
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