linux-kernel - Re: [PATCH] anon_inode: use a proper mode internally

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Message-ID: <CAGudoHF5E=PSkJ6Gf7jOeU9Ry72QyNkanqQzMdmy_Kraj=SL+w@mail.gmail.com>
Date: Mon, 7 Apr 2025 02:41:13 +0200
From: Mateusz Guzik <mjguzik@...il.com>
To: Christian Brauner <brauner@...nel.org>
Cc: Christoph Hellwig <hch@...radead.org>, Penglei Jiang <superman.xpt@...il.com>, viro@...iv.linux.org.uk, 
	jack@...e.cz, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	syzbot+5d8e79d323a13aa0b248@...kaller.appspotmail.com
Subject: Re: [PATCH] anon_inode: use a proper mode internally

On Sun, Apr 6, 2025 at 9:51 PM Christian Brauner <brauner@...nel.org> wrote:
>
> > Anyway, I'm finishing the patch and testing tomorrow and will send out
> > with all the things I mentioned (unless I find out I'm wrong).
>
> Found my notes about this. I knew I had notes about this somewhere...
> It isn't possible to execute anoymous inodes because you cannot open
> them. That includes stuff like:
>
> execveat(fd_anon_inode, "", NULL, NULL, AT_EMPTY_PATH)
>
> Look, anonymous inodes have inode->f_op set to no_open_fops which sets
> no_open() which returns ENXIO. That means any call to do_dentry_open()
> which is the endpoint of the do_open_execat() will fail. There's no
> chance to execute an anonymous inode. Unless a given subsystem overrides
> it ofc.
>
> I still agree that we need to be more coherent about this and we need to
> improve various semantical quirks I pointed out. But the exec problem
> isn't really an issue so the patch itself still seems correct to me.

Ok, that makes sense. Thanks for the explanation.

-- 
Mateusz Guzik <mjguzik gmail.com>