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

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Date:   Mon, 21 Mar 2022 17:15:02 +0800
From:   hui li <juanfengpy@...il.com>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     akpm@...ux-foundation.org, viro@...iv.linux.org.uk,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] proc: fix dentry/inode overinstantiating under /proc/${pid}/net

proc_misc_dentry_ops is a general ops for dentry under /proc, except
for "/proc/${pid}/net"，other dentries may also use there own ops too,
so I think change proc_misc_d_delete may be better?
see patch under: https://lkml.org/lkml/2022/3/17/319

Alexey Dobriyan <adobriyan@...il.com> 于2022年3月21日周一 00:24写道：
>
> 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@...il.com>
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.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)