On Fri, Aug 18, 2023 at 10:33:26AM -0700, Kees Cook wrote:
> This is a double-check I left in place, since it shouldn't have been reachable:
>
> /*
> * may_open() has already checked for this, so it should be
> * impossible to trip now. But we need to be extra cautious
> * and check again at the very end too.
> */
> err = -EACCES;
> if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) ||
> path_noexec(&file->f_path)))
> goto exit;
>
As I mentioned in my other e-mail, the check is racy -- an unlucky
enough remounting with noexec should trip over it, and probably a chmod
too.
However, that's not what triggers the warn in this case.
The ntfs image used here is intentionally corrupted and the inode at
hand has a mode of 777 (as in type not specified).
Then the type check in may_open():
switch (inode->i_mode & S_IFMT) {
fails to match anything.
This debug printk:
diff --git a/fs/namei.c b/fs/namei.c
index e56ff39a79bc..05652e8a1069 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3259,6 +3259,10 @@ static int may_open(struct mnt_idmap *idmap, const struct path *path,
if ((acc_mode & MAY_EXEC) && path_noexec(path))
return -EACCES;
break;
+ default:
+ /* bogus mode! */
+ printk(KERN_EMERG "got bogus mode inode!\n");
+ return -EACCES;
}
error = inode_permission(idmap, inode, MAY_OPEN | acc_mode);
catches it.
All that said, I think adding a WARN_ONCE here is prudent, but I
don't know if denying literally all opts is the way to go.
Do other filesystems have provisions to prevent inodes like this from
getting here?