linux-ext4 - Re: [PATCH 1/5] fscrypt: clean up and improve dentry revalidation

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Date:   Sun, 17 Mar 2019 20:38:22 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-mtd@...ts.infradead.org, linux-unionfs@...r.kernel.org,
        Sarthak Kukreti <sarthakkukreti@...omium.org>,
        Gao Xiang <gaoxiang25@...wei.com>
Subject: Re: [PATCH 1/5] fscrypt: clean up and improve dentry revalidation

On Sun, Mar 17, 2019 at 01:04:40PM -0700, Eric Biggers wrote:
> +	/*
> +	 * Ciphertext name; valid if the directory's key is still unavailable.
> +	 *
> +	 * Note: since fscrypt forbids rename() on ciphertext names, it should
> +	 * be safe to access ->d_parent directly here.

No, it is not.  Again, d_splice_alias() on buggered fs image picking a reference
to your subdirectory when doing a lookup elsewhere.  It can relocate the
damn thing, without rename() being allowed for _anything_.