[SRU][N][PATCH 6/6] proc: block mounting on top of /proc/<pid>/fdinfo/*

[Yufeng Gao]

From: Christian Brauner <brauner at kernel.org>

BugLink: https://bugs.launchpad.net/bugs/2137199

Entries under /proc/<pid>/fdinfo/* 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-v1-6-fb04e1d09f0c@kernel.org
Reviewed-by: Josef Bacik <josef at toxicpanda.com>
Signed-off-by: Christian Brauner <brauner at kernel.org>
(cherry picked from commit cf71eaa1ad18d6f6e130cda708300b587176f16f)
Signed-off-by: Yufeng Gao <yufeng.gao at canonical.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 e1734092f3bd..408a31b42c8d 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -399,8 +399,8 @@ static struct dentry *proc_fdinfo_instantiate(struct dentry *dentry,
 	inode->i_fop = &proc_fdinfo_file_operations;
 	tid_fd_update_inode(task, inode, 0);
 
-	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 *
-- 
2.43.0