Re: [PATCH] memremap: Replace 0-length array with flexible array

From: Gustavo A. R. Silva
Date: Thu Jan 05 2023 - 17:14:08 EST


I think this is the same patch:

https://lore.kernel.org/linux-hardening/YxKO%2FjY1x0xTpl4r@work/

It's actually in linux-next.

--
Gustavo

On Thu, Jan 05, 2023 at 02:01:53PM -0800, Kees Cook wrote:
> Zero-length arrays are deprecated[1]. Replace struct ethtool_rxnfc's
> "rule_locs" 0-length array with a flexible array. Detected with GCC 13,
> using -fstrict-flex-arrays=3:
>
> In file included from include/asm-generic/memory_model.h:5,
> from arch/x86/include/asm/page.h:86,
> from arch/x86/include/asm/thread_info.h:12,
> from include/linux/thread_info.h:60,
> from arch/x86/include/asm/preempt.h:9,
> from include/linux/preempt.h:78,
> from include/linux/spinlock.h:56,
> from include/linux/mmzone.h:8,
> from include/linux/gfp.h:7,
> from include/linux/mm.h:7,
> from mm/sparse-vmemmap.c:21:
> In function 'reuse_compound_section',
> inlined from 'vmemmap_populate_compound_pages' at mm/sparse-vmemmap.c:407:6,
> inlined from '__populate_section_memmap' at mm/sparse-vmemmap.c:463:7:
> mm/sparse-vmemmap.c:376:39: warning: array subscript <unknown> is outside array bounds of 'struct range[0]' [-Warray-bounds=]
> 376 | PHYS_PFN(pgmap->ranges[pgmap->nr_range].start);
> | ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
> include/linux/pfn.h:22:43: note: in definition of macro 'PHYS_PFN'
> 22 | #define PHYS_PFN(x) ((unsigned long)((x) >> PAGE_SHIFT))
> | ^
> In file included from include/linux/mm.h:31:
> include/linux/memremap.h: In function '__populate_section_memmap':
> include/linux/memremap.h:138:30: note: while referencing 'ranges'
> 138 | struct range ranges[0];
> | ^~~~~~
>
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays
>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Alex Sierra <alex.sierra@xxxxxxx>
> Cc: Felix Kuehling <Felix.Kuehling@xxxxxxx>
> Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
> Cc: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
> Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
> include/linux/memremap.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 7fcaf3180a5b..1314d9c5f05b 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -135,7 +135,7 @@ struct dev_pagemap {
> int nr_range;
> union {
> struct range range;
> - struct range ranges[0];
> + DECLARE_FLEX_ARRAY(struct range, ranges);
> };
> };
>
> --
> 2.34.1
>