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From:   hui li <juanfengpy@gmail.com>
Date:   Mon, 21 Mar 2022 17:15:02 +0800
Message-ID: <CAPmgiUK90T212icXkSJ2vSiCjXbUqO-fptNLL7NF6SMDAyTtRg@mail.gmail.com>
Subject: Re: [PATCH] proc: fix dentry/inode overinstantiating under /proc/${pid}/net
To:     Alexey Dobriyan <adobriyan@gmail.com>
Cc:     akpm@linux-foundation.org, viro@zeniv.linux.org.uk,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
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proc_misc_dentry_ops is a general ops for dentry under /proc, except
for "/proc/${pid}/net"=EF=BC=8Cother dentries may also use there own ops to=
o,
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@gmail.com> =E4=BA=8E2022=E5=B9=B43=E6=9C=8821=E6=
=97=A5=E5=91=A8=E4=B8=80 00:24=E5=86=99=E9=81=93=EF=BC=9A
>
> When a process exits, /proc/${pid}, and /proc/${pid}/net dentries are flu=
shed.
> 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 inherit=
ing
> 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 p=
roc_dir_entry **parent,
>         proc_set_user(ent, (*parent)->uid, (*parent)->gid);
>
>         ent->proc_dops =3D &proc_misc_dentry_ops;
> +       /* Revalidate everything under /proc/${pid}/net */
> +       if ((*parent)->proc_dops =3D=3D &proc_net_dentry_ops) {
> +               pde_force_lookup(ent);
> +       }
>
>  out:
>         return ent;
> --- a/fs/proc/proc_net.c
> +++ b/fs/proc/proc_net.c
> @@ -376,6 +376,9 @@ static __net_init int proc_net_ns_init(struct net *ne=
t)
>
>         proc_set_user(netd, uid, gid);
>
> +       /* Seed dentry revalidation for /proc/${pid}/net */
> +       pde_force_lookup(netd);
> +
>         err =3D -EEXIST;
>         net_statd =3D proc_net_mkdir(net, "stat", netd);
>         if (!net_statd)