[kbuild] Re: [PATCH] ntp: use memset and offsetof init

[Dan Carpenter]

Hi Yejune,

url:    https://github.com/0day-ci/linux/commits/Yejune-Deng/ntp-use-memset-and-offsetof-init/20210120-110830 
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git  3cabca87b329cbcbdf295be0094adbd72c7b1f67
config: i386-randconfig-m021-20210120 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-15) 9.3.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

smatch warnings:
kernel/time/ntp.c:232 pps_fill_timex() warn: potential pointer math issue ('txc' is a 1664 bit pointer)

vim +232 kernel/time/ntp.c

ead25417f82ed7f8 Deepa Dinamani    2018-07-02  225  static inline void pps_fill_timex(struct __kernel_timex *txc)
025b40abe715d638 Alexander Gordeev 2011-01-12  226  {
025b40abe715d638 Alexander Gordeev 2011-01-12  227  	/* PPS is not implemented, so these are zero */
a29bace5d3c06a35 Yejune Deng       2021-01-20  228  	int offset, len;
a29bace5d3c06a35 Yejune Deng       2021-01-20  229  
a29bace5d3c06a35 Yejune Deng       2021-01-20  230  	offset = offsetof(struct __kernel_timex, ppsfreq);
a29bace5d3c06a35 Yejune Deng       2021-01-20  231  	len    = offsetof(struct __kernel_timex, tai) - offset;
a29bace5d3c06a35 Yejune Deng       2021-01-20 @232  	memset(txc + offset, 0, len);
                                                               ^^^^^^^^^^^^
The warning message is badly phrased.  This needs to be:

	memset((u8 *)txc + offset, 0, len);

The current code will corrupt memory if offset is non-zero.

025b40abe715d638 Alexander Gordeev 2011-01-12  233  }

---
0-DAY CI Kernel Test Service, Intel Corporation
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