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

[Christian Brauner <brauner@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.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 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 ab243caf1b71..f6b7344b9b2e 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -220,8 +220,8 @@ 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