[PATCH] proc: fix dentry/inode overinstantiating under /proc/${pid}/net

[Alexey Dobriyan <adobriyan@gmail.com>]

When a process exits, /proc/${pid}, and /proc/${pid}/net dentries are flushed.
However some leaf dentries like /proc/${pid}/net/arp_cache aren't.
That's because respective PDEs have proc_misc_d_revalidate() hook which
returns 1 and leaves dentries/inodes in the LRU.

Force revalidation/lookup on everything under /proc/${pid}/net by inheriting
proc_net_dentry_ops.

Fixes: c6c75deda813 ("proc: fix lookup in /proc/net subdirectories after setns(2)")
Reported-by: hui li <juanfengpy@gmail.com>
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 fs/proc/generic.c  |    4 ++++
 fs/proc/proc_net.c |    3 +++
 2 files changed, 7 insertions(+)

--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -448,6 +448,10 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
 	proc_set_user(ent, (*parent)->uid, (*parent)->gid);
 
 	ent->proc_dops = &proc_misc_dentry_ops;
+	/* Revalidate everything under /proc/${pid}/net */
+	if ((*parent)->proc_dops == &proc_net_dentry_ops) {
+		pde_force_lookup(ent);
+	}
 
 out:
 	return ent;
--- a/fs/proc/proc_net.c
+++ b/fs/proc/proc_net.c
@@ -376,6 +376,9 @@ static __net_init int proc_net_ns_init(struct net *net)
 
 	proc_set_user(netd, uid, gid);
 
+	/* Seed dentry revalidation for /proc/${pid}/net */
+	pde_force_lookup(netd);
+
 	err = -EEXIST;
 	net_statd = proc_net_mkdir(net, "stat", netd);
 	if (!net_statd)