RE: [PATCH] fat: Use pointer to d_name[0] in put_user() for compat case

[David Laight]

From: David Laight
> Sent: 14 February 2022 09:12
> 
> 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.

Actually the issue is that put_user() writes a single variable
and needs a pointer to one.
So changing to:
	put_user(0, &array[0]);
is probably fine.
But the description is all wrong.

	David

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