linux-kernel - RE: [PATCH] fat: Use pointer to d_name[0] in put

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Message-ID: <49a26b7a30254d9fb9653c2f815eaa28@AcuMS.aculab.com>
Date:   Mon, 14 Feb 2022 09:12:01 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Helge Deller' <deller@....de>,
        OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>
Subject: RE: [PATCH] fat: Use pointer to d_name[0] in put_user() for compat
 case

From: Helge Deller
> Sent: 13 February 2022 22:10
> 
> The put_user(val,ptr) macro wants a pointer in the second parameter, but in
> fat_ioctl_filldir() the d_name field references a whole "array of chars".
> Usually the compiler automatically converts it and uses a pointer to that
> array, but it's more clean to explicitly give the real pointer to where someting
> is put, which is in this case the first character of the d_name[] array.

That just isn't true.

In C both x->char_array and &x->char_array[0] have the same type
'char *'.

The 'bug' is caused by put_user() trying to do:
	__typeof__(ptr) __ptr = ptr;
where __typeof__ is returning char[n] not char *.

I've tried a few things but can't get __typeof__ to
generate a suitable type for both a simple type and array.

	David

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