linux-hardening - Re: [PATCH][next] fsnotify: Avoid -Wflex-array-member-not-at-end warning

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Message-ID: <34889a1a-4c8f-4c4d-865a-f947569f8d9c@embeddedor.com>
Date: Wed, 6 Mar 2024 09:42:50 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Amir Goldstein <amir73il@...il.com>, Kees Cook <keescook@...omium.org>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>, Jan Kara <jack@...e.cz>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] fsnotify: Avoid -Wflex-array-member-not-at-end
 warning

On 3/6/24 01:36, Amir Goldstein wrote:
> On Wed, Mar 6, 2024 at 1:52 AM Kees Cook <keescook@...omium.org> wrote:
>>
>> On Tue, Mar 05, 2024 at 04:18:46PM -0600, Gustavo A. R. Silva wrote:
>>> -Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
>>> ready to enable it globally.
>>>
>>> There is currently a local structure `f` that is using a flexible
>>> `struct file_handle` as header for an on-stack place-holder for the
>>> flexible-array member `unsigned char f_handle[];`.
>>>
>>> struct {
>>>        struct file_handle handle;
>>>        u8 pad[MAX_HANDLE_SZ];
>>> } f;
>>
>> This code pattern is "put a flex array struct on the stack", but we have
>> a macro for this now:
>>
>> DEFINE_FLEX(struct file_handle, handle, f_handle, MAX_HANDLE_SZ);
>>
>> And you can even include the initializer:
>>
>> _DEFINE_FLEX(struct file_handle, handle, f_handle, MAX_HANDLE_SZ,
>>               = { .handle_bytes = MAX_HANDLE_SZ });
>>
> 
> Indeed that looks much nicer.

Yeah, I'll probably wait for this to land before I send a v2:

https://lore.kernel.org/linux-hardening/20240306010746.work.678-kees@kernel.org/

Thanks
--
Gustavo