Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.34 as permitted sender) client-ip=23.128.96.34;
Date:   Tue, 5 Dec 2023 12:38:35 +0100
From:   Christian Brauner <brauner@kernel.org>
To:     Kees Cook <keescook@chromium.org>
Cc:     Al Viro <viro@zeniv.linux.org.uk>,
        "Guilherme G. Piccoli" <gpiccoli@igalia.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-fsdevel@vger.kernel.org, Tony Luck <tony.luck@intel.com>,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH 3/5] fs: Add DEFINE_FREE for struct inode
Message-ID: <20231205-horchen-gemieden-8013e0f30883@brauner>
References: <20231202211535.work.571-kees@kernel.org>
 <20231202212217.243710-3-keescook@chromium.org>
 <20231202212846.GQ38156@ZenIV>
 <202312021331.D2DFBF153@keescook>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <202312021331.D2DFBF153@keescook>
Precedence: bulk

On Sat, Dec 02, 2023 at 01:34:32PM -0800, Kees Cook wrote:
> 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...

If we wanted to do this properly then we would need to emulate consume
or move semantics like Rust has. So a cleanup function for inodes based
on scope for example and then another primitive that transfers/moves
ownership of that refcount to the consumer. Usually this is emulate by
stuff like TAKE_POINTER() and similar stuff in userspace. But I'm not
sure how pleasant it would be to do this cleanly.