Re: [bpf-next v4 1/2] bpf: Add bpf_copy_from_user_str kfunc

[kernel test robot <lkp@intel.com>]

Hi Jordan,

kernel test robot noticed the following build warnings:

[auto build test WARNING on bpf-next/master]

url:    https://github.com/intel-lab-lkp/linux/commits/Jordan-Rome/bpf-Add-tests-for-bpf_copy_from_user_str-kfunc/20240814-232043
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
patch link:    https://lore.kernel.org/r/20240814004531.352157-1-linux%40jordanrome.com
patch subject: [bpf-next v4 1/2] bpf: Add bpf_copy_from_user_str kfunc
config: i386-buildonly-randconfig-002-20240815 (https://download.01.org/0day-ci/archive/20240815/202408151130.79yPpdxy-lkp@intel.com/config)
compiler: clang version 18.1.5 (https://github.com/llvm/llvm-project 617a15a9eac96088ae5e9134248d8236e34b91b1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240815/202408151130.79yPpdxy-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202408151130.79yPpdxy-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> kernel/bpf/helpers.c:2975:4: warning: add explicit braces to avoid dangling else [-Wdangling-else]
    2975 |                         else
         |                         ^
   1 warning generated.


vim +2975 kernel/bpf/helpers.c

  2941	
  2942	/**
  2943	 * bpf_copy_from_user_str() - Copy a string from an unsafe user address
  2944	 * @dst:             Destination address, in kernel space.  This buffer must be at
  2945	 *                   least @dst__szk bytes long.
  2946	 * @dst__szk:        Maximum number of bytes to copy, including the trailing NUL.
  2947	 * @unsafe_ptr__ign: Source address, in user space.
  2948	 * @flags:           The only supported flag is BPF_ZERO_BUFFER
  2949	 *
  2950	 * Copies a NUL-terminated string from userspace to BPF space. If user string is
  2951	 * too long this will still ensure zero termination in the dst buffer unless
  2952	 * buffer size is 0.
  2953	 *
  2954	 * If BPF_ZERO_BUFFER flag is set, memset the tail of @dst to 0 on success.
  2955	 */
  2956	__bpf_kfunc int bpf_copy_from_user_str(void *dst, u32 dst__szk, const void __user *unsafe_ptr__ign, u64 flags)
  2957	{
  2958		int ret;
  2959		int count;
  2960	
  2961		if (unlikely(!dst__szk))
  2962			return 0;
  2963	
  2964		count = dst__szk - 1;
  2965		if (unlikely(!count)) {
  2966			((char *)dst)[0] = '\0';
  2967			return 1;
  2968		}
  2969	
  2970		ret = strncpy_from_user(dst, unsafe_ptr__ign, count);
  2971		if (ret >= 0) {
  2972			if (ret <= count)
  2973				if (flags & BPF_ZERO_BUFFER)
  2974					memset((char *)dst + ret, 0, dst__szk - ret);
> 2975				else
  2976					((char *)dst)[ret] = '\0';
  2977			ret++;
  2978		}
  2979	
  2980		return ret;
  2981	}
  2982	

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