linux-kernel - Re: [PATCH 05/20] afs: Implement @sys substitution handling

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Message-ID: <20180406065118.GZ30522@ZenIV.linux.org.uk>
Date:   Fri, 6 Apr 2018 07:51:18 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     David Howells <dhowells@...hat.com>
Cc:     torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
        linux-afs@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/20] afs: Implement @sys substitution handling

On Thu, Apr 05, 2018 at 09:30:04PM +0100, David Howells wrote:
> +static struct dentry *afs_lookup_atsys(struct inode *dir, struct dentry *dentry,
> +				       struct key *key)
> +{

> +		ret = lookup_one_len(buf, parent, len);

Er...  Parent is locked only shared here and lookup_one_len() seriously depends
upon exclusive lock.  As it is, race with lookup of the full name will mess the
things up very badly.