linux-kernel - Re: [PATCH 2/2] VFS: add common error checks to lookup_one_qstr

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Message-ID: <20250212031608.GL1977892@ZenIV>
Date: Wed, 12 Feb 2025 03:16:08 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: NeilBrown <neilb@...e.de>
Cc: Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Trond Myklebust <trondmy@...nel.org>,
	Anna Schumaker <anna@...nel.org>,
	Namjae Jeon <linkinjeon@...nel.org>,
	Steve French <sfrench@...ba.org>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Tom Talpey <tom@...pey.com>, Paul Moore <paul@...l-moore.com>,
	Eric Paris <eparis@...hat.com>, linux-kernel@...r.kernel.org,
	linux-bcachefs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
	audit@...r.kernel.org
Subject: Re: [PATCH 2/2] VFS: add common error checks to
 lookup_one_qstr_excl()

On Fri, Feb 07, 2025 at 02:36:48PM +1100, NeilBrown wrote:
> @@ -1690,6 +1692,15 @@ struct dentry *lookup_one_qstr_excl(const struct qstr *name,
>  		dput(dentry);
>  		dentry = old;
>  	}
> +found:

... and if ->lookup() returns an error, this will blow up (as bot has just
reported).

> +	if (d_is_negative(dentry) && !(flags & LOOKUP_CREATE)) {
> +		dput(dentry);
> +		return ERR_PTR(-ENOENT);
> +	}
> +	if (d_is_positive(dentry) && (flags & LOOKUP_EXCL)) {
> +		dput(dentry);
> +		return ERR_PTR(-EEXIST);
> +	}


> @@ -4077,27 +4084,13 @@ static struct dentry *filename_create(int dfd, struct filename *name,
>  	 * '/', and a directory wasn't requested.
>  	 */
>  	if (last.name[last.len] && !want_dir)
> -		create_flags = 0;
> +		create_flags &= ~LOOKUP_CREATE;

See the patch I've posted in earlier thread; the entire "strip LOOKUP_CREATE"
thing is wrong.