[PATCH] hostfs: Fix only passing host root in boot stage with new mount

[Geoffrey Thorpe]

(This time, responding in plain text so the list-server doesn't reject. 
oops.)

Yes, I've tested your patch and it has fixed the problem for me. Thanks


On 2025-10-11 05:22, Hongbo Li wrote:
> In the old mount proceedure, hostfs could only pass root directory during
> boot. This is because it constructed the root directory using the @root_ino
> event without any mount options. However, when using it with the new mount
> API, this step is no longer triggered. As a result, if users mounts without
> specifying any mount options, the @host_root_path remains uninitialized. To
> prevent this issue, the @host_root_path should be initialized at the time
> of allocation.
>
> Reported-by: Geoffrey Thorpe <geoff at geoffthorpe.net>
> Closes: https://lore.kernel.org/all/643333a0-f434-42fb-82ac-d25a0b56f3b7@geoffthorpe.net/
> Fixes: cd140ce9f611 ("hostfs: convert hostfs to use the new mount API")
> Signed-off-by: Hongbo Li <lihongbo22 at huawei.com>
> ---
>   fs/hostfs/hostfs_kern.c | 29 ++++++++++++++++++-----------
>   1 file changed, 18 insertions(+), 11 deletions(-)
>
> diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c
> index 1e1acf5775ab..86455eebbf6c 100644
> --- a/fs/hostfs/hostfs_kern.c
> +++ b/fs/hostfs/hostfs_kern.c
> @@ -979,7 +979,7 @@ static int hostfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
>   {
>   	struct hostfs_fs_info *fsi = fc->s_fs_info;
>   	struct fs_parse_result result;
> -	char *host_root;
> +	char *host_root, *tmp_root;
>   	int opt;
>   
>   	opt = fs_parse(fc, hostfs_param_specs, param, &result);
> @@ -990,11 +990,13 @@ static int hostfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
>   	case Opt_hostfs:
>   		host_root = param->string;
>   		if (!*host_root)
> -			host_root = "";
> -		fsi->host_root_path =
> -			kasprintf(GFP_KERNEL, "%s/%s", root_ino, host_root);
> -		if (fsi->host_root_path == NULL)
> +			break;
> +		tmp_root = kasprintf(GFP_KERNEL, "%s%s",
> +				     fsi->host_root_path, host_root);
> +		if (!tmp_root)
>   			return -ENOMEM;
> +		kfree(fsi->host_root_path);
> +		fsi->host_root_path = tmp_root;
>   		break;
>   	}
>   
> @@ -1004,17 +1006,17 @@ static int hostfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
>   static int hostfs_parse_monolithic(struct fs_context *fc, void *data)
>   {
>   	struct hostfs_fs_info *fsi = fc->s_fs_info;
> -	char *host_root = (char *)data;
> +	char *tmp_root, *host_root = (char *)data;
>   
>   	/* NULL is printed as '(null)' by printf(): avoid that. */
>   	if (host_root == NULL)
> -		host_root = "";
> +		return 0;
>   
> -	fsi->host_root_path =
> -		kasprintf(GFP_KERNEL, "%s/%s", root_ino, host_root);
> -	if (fsi->host_root_path == NULL)
> +	tmp_root = kasprintf(GFP_KERNEL, "%s%s", fsi->host_root_path, host_root);
> +	if (!tmp_root)
>   		return -ENOMEM;
> -
> +	kfree(fsi->host_root_path);
> +	fsi->host_root_path = tmp_root;
>   	return 0;
>   }
>   
> @@ -1049,6 +1051,11 @@ static int hostfs_init_fs_context(struct fs_context *fc)
>   	if (!fsi)
>   		return -ENOMEM;
>   
> +	fsi->host_root_path = kasprintf(GFP_KERNEL, "%s/", root_ino);
> +	if (!fsi->host_root_path) {
> +		kfree(fsi);
> +		return -ENOMEM;
> +	}
>   	fc->s_fs_info = fsi;
>   	fc->ops = &hostfs_context_ops;
>   	return 0;