Re: [PATCH next] ext4: Fix diagnostic printf formats

[David Laight]

On Fri, 27 Mar 2026 12:48:56 +0200
Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:

> On Thu, Mar 26, 2026 at 08:18:04PM +0000, david.laight.linux@xxxxxxxxx wrote:
> 
> > The formats for non-terminated names should be "%.*s" not "%*.s".
> > The kernel currently treats "%*.s" as equivalent to "%*s" whereas
> > userspace requires it be equivalent to "%*.0s".
> > Neither is correct here.  
> 
> This entire code seems was never tested properly and it's a dead code
> until one defines manually DX_DEBUG. It also has tons of plain printk()
> calls that may behave differently if the first character is not printable
> but maps to the level of printk().
> 
> I'm not sure how your patch helps with all that, but apparently the
> printed data has to be NUL-terminated, otherwise I have no idea how
> it was ever working without crashes.
> 

I noticed that as well.
I suspect it way have worked for the person that wrote it because the
name strings all happened to be NUL terminated.
There is certainly likely to be a '\0' before you 'fall off' mapped
memory and crash - so maybe they just ignored the extra characters.

Clearly the other option is to delete it all.
But regardless the format string is wrong.

	David