vfs: read file_handle only once in handle_to_path

We used to read file_handle twice. Once to get the amount of extra bytes, and once to fetch the entire structure. This may be problematic since we do size verifications only after the first read, so if the number of extra bytes changes in userspace between the first and second calls, we'll have an incoherent view of file_handle. Instead, read the constant size once, and copy that over to the final structure without having to re-read it again. Signed-off-by: Sasha Levin <[email protected]> Cc: Al Viro <[email protected]> Cc: [email protected] Signed-off-by: Linus Torvalds <[email protected]>
jimmycarry · Jun 2, 2015 · 161f873 · 161f873
1 parent f18c34e
commit 161f873
Showing 1 changed file with 3 additions and 2 deletions.
diff --git a/fs/fhandle.c b/fs/fhandle.c
@@ -195,8 +195,9 @@ static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
 		goto out_err;
 	}
 	/* copy the full handle */
-	if (copy_from_user(handle, ufh,
-			   sizeof(struct file_handle) +
+	*handle = f_handle;
+	if (copy_from_user(&handle->f_handle,
+			   &ufh->f_handle,
 			   f_handle.handle_bytes)) {
 		retval = -EFAULT;
 		goto out_handle;