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

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Message-ID: <20231202214212.GR38156@ZenIV>
Date: Sat, 2 Dec 2023 21:42:12 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Kees Cook <keescook@...omium.org>
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 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))" ?

No.  I would rather *not* see IS_ERR_OR_NULL anywhere, but that's
a separate rant.

> > 	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/

I'll poke around and see what I can suggest; said that, one thing I have
spotted there on the quick look is that you are exposing hashed dentry associated
with your inode before you set its ->i_private.  Have an open() hit just after
that d_add() and this
static int pstore_file_open(struct inode *inode, struct file *file)
{
        struct pstore_private *ps = inode->i_private;
        struct seq_file *sf;
        int err;
        const struct seq_operations *sops = NULL;

        if (ps->record->type == PSTORE_TYPE_FTRACE)
... with happily oops on you.