Re: [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 <ge...@geoffthorpe.net>
Closes: 
https://lore.kernel.org/all/643333a0-f434-42fb-82ac-d25a0b56f...@geoffthorpe.net/
Fixes: cd140ce9f611 ("hostfs: convert hostfs to use the new mount API")
Signed-off-by: Hongbo Li <lihongb...@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;