linux-kernel - Re: do_change_type(): refuse to operate on unmounted/not ours mounts

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Message-ID: <CANaxB-xXgW1FEj6ydBT2=cudTbP=fX6x8S53zNkWcw1poL=L2A@mail.gmail.com>
Date: Thu, 24 Jul 2025 13:02:48 -0700
From: Andrei Vagin <avagin@...il.com>
To: Al Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>
Cc: linux-fsdevel <linux-fsdevel@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	criu@...ts.linux.dev
Subject: Re: do_change_type(): refuse to operate on unmounted/not ours mounts

Hi Al and Christian,

The commit 12f147ddd6de ("do_change_type(): refuse to operate on
unmounted/not ours mounts") introduced an ABI backward compatibility
break. CRIU depends on the previous behavior, and users are now
reporting criu restore failures following the kernel update. This change
has been propagated to stable kernels. Is this check strictly required?
Would it be possible to check only if the current process has
CAP_SYS_ADMIN within the mount user namespace?

Thanks,
Andrei