linux-kernel - Re: [PATCH 2/2] virtiofs: Improve error handling in virtio_fs_get

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Date: Tue, 2 Jan 2024 15:21:33 -0500
From: Vivek Goyal <vgoyal@...hat.com>
To: Markus Elfring <Markus.Elfring@....de>
Cc: virtualization@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
	kernel-janitors@...r.kernel.org, Miklos Szeredi <miklos@...redi.hu>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH 2/2] virtiofs: Improve error handling in
 virtio_fs_get_tree()

On Fri, Dec 29, 2023 at 09:38:47AM +0100, Markus Elfring wrote:
> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Fri, 29 Dec 2023 09:15:07 +0100
> 
> The kfree() function was called in two cases by
> the virtio_fs_get_tree() function during error handling
> even if the passed variable contained a null pointer.
> This issue was detected by using the Coccinelle software.
> 
> * Thus use another label.
> 
> * Move an error code assignment into an if branch.
> 
> * Delete an initialisation (for the variable “fc”)
>   which became unnecessary with this refactoring.
> 
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>

As Matthew said that kfree(NULL) is perfectly acceptable usage in kernel,
so I really don't feel that this patch is required. Current code looks
good as it is.

Thanks
Vivek

> ---
>  fs/fuse/virtio_fs.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
> index 2f8ba9254c1e..0746f54ec743 100644
> --- a/fs/fuse/virtio_fs.c
> +++ b/fs/fuse/virtio_fs.c
> @@ -1415,10 +1415,10 @@ static int virtio_fs_get_tree(struct fs_context *fsc)
>  {
>  	struct virtio_fs *fs;
>  	struct super_block *sb;
> -	struct fuse_conn *fc = NULL;
> +	struct fuse_conn *fc;
>  	struct fuse_mount *fm;
>  	unsigned int virtqueue_size;
> -	int err = -EIO;
> +	int err;
> 
>  	/* This gets a reference on virtio_fs object. This ptr gets installed
>  	 * in fc->iq->priv. Once fuse_conn is going away, it calls ->put()
> @@ -1431,13 +1431,15 @@ static int virtio_fs_get_tree(struct fs_context *fsc)
>  	}
> 
>  	virtqueue_size = virtqueue_get_vring_size(fs->vqs[VQ_REQUEST].vq);
> -	if (WARN_ON(virtqueue_size <= FUSE_HEADER_OVERHEAD))
> -		goto out_err;
> +	if (WARN_ON(virtqueue_size <= FUSE_HEADER_OVERHEAD)) {
> +		err = -EIO;
> +		goto lock_mutex;
> +	}
> 
>  	err = -ENOMEM;
>  	fc = kzalloc(sizeof(*fc), GFP_KERNEL);
>  	if (!fc)
> -		goto out_err;
> +		goto lock_mutex;
> 
>  	fm = kzalloc(sizeof(*fm), GFP_KERNEL);
>  	if (!fm)
> @@ -1476,6 +1478,7 @@ static int virtio_fs_get_tree(struct fs_context *fsc)
> 
>  out_err:
>  	kfree(fc);
> +lock_mutex:
>  	mutex_lock(&virtio_fs_mutex);
>  	virtio_fs_put(fs);
>  	mutex_unlock(&virtio_fs_mutex);
> --
> 2.43.0
>