Re: [PATCH v3] sysfs: Unconditionally use vmalloc for buffer

[Nathan Chancellor <nathan@kernel.org>]

On Thu, Apr 01, 2021 at 02:41:37PM +0800, kernel test robot wrote:
> Hi Kees,
> 
> I love your patch! Perhaps something to improve:
> 
> [auto build test WARNING on driver-core/driver-core-testing]
> [also build test WARNING on kees/for-next/pstore v5.12-rc5 next-20210331]
> [cannot apply to hnaz-linux-mm/master]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch]
> 
> url:    https://github.com/0day-ci/linux/commits/Kees-Cook/sysfs-Unconditionally-use-vmalloc-for-buffer/20210401-102455
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git d225ef6fda7ce9ff7d28764bd1cceea2d0215e8b
> config: powerpc-randconfig-r001-20210401 (attached as .config)
> compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 1c268a8ff4e90a85d0e634350b1104080614cf2b)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # install powerpc cross compiling tool for clang build
>         # apt-get install binutils-powerpc-linux-gnu
>         # https://github.com/0day-ci/linux/commit/c80ca56c15314908ebc1881678da3b36e007a2f4
>         git remote add linux-review https://github.com/0day-ci/linux
>         git fetch --no-tags linux-review Kees-Cook/sysfs-Unconditionally-use-vmalloc-for-buffer/20210401-102455
>         git checkout c80ca56c15314908ebc1881678da3b36e007a2f4
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=powerpc 
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
> 
> All warnings (new ones prefixed by >>):
> 
> >> fs/sysfs/file.c:52:14: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
>            return NULL + !*ppos;
>                   ~~~~ ^
>    1 warning generated.
> 

Arnd addressed other warnings of this nature in this patch:

https://lore.kernel.org/r/20201028151202.3074398-1-arnd@kernel.org/

which it seems never got picked up :(

Cheers,
Nathan

> vim +52 fs/sysfs/file.c
> 
>     35	
>     36	/*
>     37	 * To be proactively defensive against sysfs show() handlers that do not
>     38	 * correctly stay within their PAGE_SIZE buffer, use the vmap area to gain
>     39	 * the trailing guard page which will stop linear buffer overflows.
>     40	 */
>     41	static void *sysfs_kf_seq_start(struct seq_file *sf, loff_t *ppos)
>     42	{
>     43		struct kernfs_open_file *of = sf->private;
>     44		struct kernfs_node *kn = of->kn;
>     45	
>     46		WARN_ON_ONCE(sf->buf);
>     47		sf->buf = __vmalloc(kn->attr.size, GFP_KERNEL_ACCOUNT);
>     48		if (!sf->buf)
>     49			return ERR_PTR(-ENOMEM);
>     50		sf->size = kn->attr.size;
>     51	
>   > 52		return NULL + !*ppos;
>     53	}
>     54	
> 
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org