linux-kernel - [PATCH 06/17] fsinfo: Add a uniquifier ID to struct mount [ver #20]

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Message-ID: <159559774044.2144584.14085699755046222864.stgit@warthog.procyon.org.uk>
Date:   Fri, 24 Jul 2020 14:35:40 +0100
From:   David Howells <dhowells@...hat.com>
To:     torvalds@...ux-foundation.org, viro@...iv.linux.org.uk
Cc:     dhowells@...hat.com, raven@...maw.net, mszeredi@...hat.com,
        christian@...uner.io, jannh@...gle.com, darrick.wong@...cle.com,
        kzak@...hat.com, jlayton@...hat.com, linux-api@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 06/17] fsinfo: Add a uniquifier ID to struct mount [ver #20]

Add a uniquifier ID to struct mount that is effectively unique over the
kernel lifetime to deal around mnt_id values being reused.  This can then
be exported through fsinfo() to allow detection of replacement mounts that
happen to end up with the same mount ID.

The normal mount handle is still used for referring to a particular mount.

Signed-off-by: David Howells <dhowells@...hat.com>
---

 fs/mount.h     |    3 +++
 fs/namespace.c |    3 +++
 2 files changed, 6 insertions(+)

diff --git a/fs/mount.h b/fs/mount.h
index 1c777f651446..c3e0bb6e5782 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -79,6 +79,9 @@ struct mount {
 	int mnt_expiry_mark;		/* true if marked for expiry */
 	struct hlist_head mnt_pins;
 	struct hlist_head mnt_stuck_children;
+#ifdef CONFIG_FSINFO
+	u64	mnt_unique_id;		/* ID unique over lifetime of kernel */
+#endif
 #ifdef CONFIG_MOUNT_NOTIFICATIONS
 	atomic_t mnt_topology_changes;	/* Number of topology changes applied */
 	atomic_t mnt_attr_changes;	/* Number of attribute changes applied */
diff --git a/fs/namespace.c b/fs/namespace.c
index b2b9920ffd3c..1db8a64cd76f 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -115,6 +115,9 @@ static int mnt_alloc_id(struct mount *mnt)
 	if (res < 0)
 		return res;
 	mnt->mnt_id = res;
+#ifdef CONFIG_FSINFO
+	mnt->mnt_unique_id = atomic64_inc_return(&vfs_unique_counter);
+#endif
 	return 0;
 }