[Devel] [PATCH vz9 5/6] proc: block mounting on top of /proc/<pid>/fd/*

[Vasileios Almpanis]

From: Christian Brauner <brauner at kernel.org>

Entries under /proc/<pid>/fd/* are ephemeral and may go away before the
process dies. As such allowing them to be used as mount points creates
the ability to leak mounts that linger until the process dies with no
ability to unmount them until then. Don't allow using them as
mountpoints.

Link: https://lore.kernel.org/r/20240806-work-procfs-v1-5-fb04e1d09f0c@kernel.org
Reviewed-by: Josef Bacik <josef at toxicpanda.com>
Signed-off-by: Christian Brauner <brauner at kernel.org>
(cherry picked from commit 0175ac500806a8827f728a675943640f915c422a)

https://virtuozzo.atlassian.net/browse/VSTOR-121919
Signed-off-by: Vasileios Almpanis <vasileios.almpanis at virtuozzo.com>
---
 fs/proc/fd.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 0ffe6947b46c..5d6252dbefd1 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -202,8 +202,8 @@ static struct dentry *proc_fd_instantiate(struct dentry *dentry,
 	ei->op.proc_get_link = proc_fd_link;
 	tid_fd_update_inode(task, inode, data->mode);
 
-	d_set_d_op(dentry, &tid_fd_dentry_operations);
-	return d_splice_alias(inode, dentry);
+	return proc_splice_unmountable(inode, dentry,
+				       &tid_fd_dentry_operations);
 }
 
 static struct dentry *proc_lookupfd_common(struct inode *dir,
-- 
2.43.0