linux-kernel - Re: [PATCH v4] proc: Allow pid_revalidate() during LOOKUP

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Message-ID: <20210105174531.GW3579531@ZenIV.linux.org.uk>
Date:   Tue, 5 Jan 2021 17:45:31 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Stephen Brennan <stephen.s.brennan@...cle.com>
Cc:     Alexey Dobriyan <adobriyan@...il.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org,
        Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>, selinux@...r.kernel.org,
        Casey Schaufler <casey@...aufler-ca.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v4] proc: Allow pid_revalidate() during LOOKUP_RCU

On Tue, Jan 05, 2021 at 04:50:05PM +0000, Al Viro wrote:

> struct dentry *d_find_alias_rcu(struct inode *inode)
> {
> 	struct hlist_head *l = &inode->i_dentry;
>         struct dentry *de = NULL;
> 
> 	spin_lock(&inode->i_lock);
> 	// ->i_dentry and ->i_rcu are colocated, but the latter won't be
> 	// used without having I_FREEING set, which means no aliases left
> 	if (inode->i_state & I_FREEING) {
> 		spin_unlock(&inode->i_lock);
> 		return NULL;
> 	}
> 	// we can safely access inode->i_dentry
>         if (hlist_empty(p)) {

	if (hlist_empty(l)) {

obviously...