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RE: [PATCH][next] treewide: uapi: Replace zero-length arrays with flexib

To: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>, Kees Cook <keescook@xxxxxxxxxxxx>, <linux-kernel@xxxxxxxxxxxxxxx>
Subject: RE: [PATCH][next] treewide: uapi: Replace zero-length arrays with flexible-array members
Cc: <x86@xxxxxxxxxx>, <dm-devel@xxxxxxxxxx>, <linux-m68k@xxxxxxxxxxxxxxxxxxxx>, <linux-mips@xxxxxxxxxxxxxxx>, <linux-s390@xxxxxxxxxxxxxxx>, <kvm@xxxxxxxxxxxxxxx>, <intel-gfx@xxxxxxxxxxxxxxxxxxxxx>, <dri-devel@xxxxxxxxxxxxxxxxxxxxx>, <netdev@xxxxxxxxxxxxxxx>, <bpf@xxxxxxxxxxxxxxx>, <linux-btrfs@xxxxxxxxxxxxxxx>, <linux-can@xxxxxxxxxxxxxxx>, <linux-fsdevel@xxxxxxxxxxxxxxx>, <linux1394-devel@xxxxxxxxxxxxxxxxxxxxx>, <io-uring@xxxxxxxxxxxxxxx>, <lvs-devel@xxxxxxxxxxxxxxx>, <linux-mtd@xxxxxxxxxxxxxxxxxxx>, <kasan-dev@xxxxxxxxxxxxxxxx>, <linux-mmc@xxxxxxxxxxxxxxx>, <nvdimm@xxxxxxxxxxxxxxx>, <netfilter-devel@xxxxxxxxxxxxxxx>, <coreteam@xxxxxxxxxxxxx>, <linux-perf-users@xxxxxxxxxxxxxxx>, <linux-raid@xxxxxxxxxxxxxxx>, <linux-sctp@xxxxxxxxxxxxxxx>, <linux-stm32@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>, <linux-scsi@xxxxxxxxxxxxxxx>, <target-devel@xxxxxxxxxxxxxxx>, <linux-usb@xxxxxxxxxxxxxxx>, <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, <v9fs-developer@xxxxxxxxxxxxxxxxxxxxx>, <linux-rdma@xxxxxxxxxxxxxxx>, <alsa-devel@xxxxxxxxxxxxxxxx>, "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>, <linux-hardening@xxxxxxxxxxxxxxx>
From: Dan Williams <dan.j.williams@xxxxxxxxx>
Date: Mon, 27 Jun 2022 15:31:42 -0700
Gustavo A. R. Silva wrote:
> There is a regular need in the kernel to provide a way to declare
> having a dynamically sized set of trailing elements in a structure.
> Kernel code should always use “flexible array members”[1] for these
> cases. The older style of one-element or zero-length arrays should
> no longer be used[2].
> 
> This code was transformed with the help of Coccinelle:
> (linux-5.19-rc2$ spatch --jobs $(getconf _NPROCESSORS_ONLN) --sp-file 
> script.cocci --include-headers --dir . > output.patch)
> 
> @@
> identifier S, member, array;
> type T1, T2;
> @@
> 
> struct S {
>   ...
>   T1 member;
>   T2 array[
> - 0
>   ];
> };
> 
> -fstrict-flex-arrays=3 is coming and we need to land these changes
> to prevent issues like these in the short future:
> 
> ../fs/minix/dir.c:337:3: warning: 'strcpy' will always overflow; destination 
> buffer has size 0,
> but the source string has length 2 (including NUL byte) [-Wfortify-source]
>               strcpy(de3->name, ".");
>               ^
> 
> Since these are all [0] to [] changes, the risk to UAPI is nearly zero. If
> this breaks anything, we can use a union with a new member name.
> 
> [1] https://en.wikipedia.org/wiki/Flexible_array_member
> [2] 
> https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays
> 
> Link: https://github.com/KSPP/linux/issues/78
> Build-tested-by: 
> https://lore.kernel.org/lkml/62b675ec.wKX6AOZ6cbE71vtF%25lkp@xxxxxxxxx/
> Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> ---
> Hi all!
> 
> JFYI: I'm adding this to my -next tree. :)
> 
[..]
>  include/uapi/linux/ndctl.h                    | 10 +--

For ndctl.h

Acked-by: Dan Williams <dan.j.williams@xxxxxxxxx>

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