linux-hardening - Re: [PATCH 3/5] fs: Add DEFINE

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Date: Sat, 2 Dec 2023 13:34:32 -0800
From: Kees Cook <keescook@...omium.org>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
	Christian Brauner <brauner@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-fsdevel@...r.kernel.org, Tony Luck <tony.luck@...el.com>,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 3/5] fs: Add DEFINE_FREE for struct inode

On Sat, Dec 02, 2023 at 09:28:46PM +0000, Al Viro wrote:
> On Sat, Dec 02, 2023 at 01:22:13PM -0800, Kees Cook wrote:
> > Allow __free(iput) markings for easier cleanup on inode allocations.
> 
> NAK.  That's a bloody awful idea for that particular data type, since
> 	1) ERR_PTR(...) is not uncommon and passing it to iput() is a bug.

Ah, sounds like instead of "if (_T)", you'd rather see
"if (!IS_ERR_OR_NULL(_T))" ?

> 	2) the common pattern is to have reference-consuming primitives,
> with failure exits normally *not* having to do iput() at all.

This I'm not following. If I make a call to "new_inode(sb)" that I end
up not using, I need to call "iput()" in it...

How should this patch be written to avoid the iput() on failure?
https://lore.kernel.org/all/20231202212217.243710-4-keescook@chromium.org/

-Kees

-- 
Kees Cook