[PATCH 5.15.y 2/6] proc: add proc_splice_unmountable()

[Sasha Levin <sashal@kernel.org>]

From: Christian Brauner <brauner@kernel.org>

[ Upstream commit 32a0a965b8a5b7b505babae2ee10c513ede376d8 ]

Add a tiny procfs helper to splice a dentry that cannot be mounted upon.

Link: https://lore.kernel.org/r/20240806-work-procfs-v1-3-fb04e1d09f0c@kernel.org
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Stable-dep-of: eeecea75ece2 ("proc: don't let an entry below /proc/<pid>/net be a mountpoint")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/proc/internal.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index 9c4a5540296fc..2c652681172b8 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -332,3 +332,16 @@ static inline void pde_force_lookup(struct proc_dir_entry *pde)
 	/* /proc/net/ entries can be changed under us by setns(CLONE_NEWNET) */
 	pde->proc_dops = &proc_net_dentry_ops;
 }
+
+/*
+ * Add a new procfs dentry that can't serve as a mountpoint. That should
+ * encompass anything that is ephemeral and can just disappear while the
+ * process is still around.
+ */
+static inline struct dentry *proc_splice_unmountable(struct inode *inode,
+		struct dentry *dentry, const struct dentry_operations *d_ops)
+{
+	d_set_d_op(dentry, d_ops);
+	dont_mount(dentry);
+	return d_splice_alias(inode, dentry);
+}
-- 
2.53.0