Re: [RFC PATCH v3 2/3] fs: debugfs: Add write functionality to debugfs blobs

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On 13/6/23 17:59, Greg KH wrote:
On Mon, Jun 12, 2023 at 09:51:38PM +0000, Avadhut Naik wrote:
  /**
- * debugfs_create_blob - create a debugfs file that is used to read a binary blob
+ * debugfs_create_blob - create a debugfs file that is used to read and write
+ * a binary blob
   * @name: a pointer to a string containing the name of the file to create.
- * @mode: the read permission that the file should have (other permissions are
- *	  masked out)
+ * @mode: the permission that the file should have
   * @parent: a pointer to the parent dentry for this file.  This should be a
   *          directory dentry if set.  If this parameter is %NULL, then the
   *          file will be created in the root of the debugfs filesystem.
@@ -992,7 +1010,7 @@ static const struct file_operations fops_blob = {
   *
   * This function creates a file in debugfs with the given name that exports
   * @blob->data as a binary blob. If the @mode variable is so set it can be
- * read from. Writing is not supported.
+ * read from and written to.
   *
   * This function will return a pointer to a dentry if it succeeds.  This
   * pointer must be passed to the debugfs_remove() function when the file is
@@ -1007,7 +1025,7 @@ struct dentry *debugfs_create_blob(const char *name, umode_t mode,
  				   struct dentry *parent,
  				   struct debugfs_blob_wrapper *blob)
  {
-	return debugfs_create_file_unsafe(name, mode & 0444, parent, blob, &fops_blob);
+	return debugfs_create_file_unsafe(name, mode, parent, blob, &fops_blob);

Have you audited all calls to this function to verify that you haven't
just turned on write access to some debugfs files?

I just did, it is one of S_IRUGO/S_IRUSR/0444/0400/(S_IFREG | 0444). So we are quite safe here. Except (S_IFREG | 0444) in drivers/platform/chrome/cros_ec_debugfs.c which seems wrong as debugfs files are not regular files.

Why not rename this to debugfs_create_blob_wo() and then make a new
debugfs_create_blob_rw() call to ensure that it all is ok?

It is already taking the mode for this purpose. imho just cros_ec_create_panicinfo()'s debugfs_create_blob("panicinfo", S_IFREG | 0444,...) needs fixing.


thanks,

greg k-h

--
Alexey



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