Re: [PATCH 4/9] Implement fsopen() to prepare for a mount

From: David Howells
Date: Thu May 04 2017 - 08:55:36 EST

Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> wrote:

> OK, mc->error must be static data, so no lifetime problems.

Technically, mc->error is only good as long as we hold a ref on its module.
It might be better to copy the string, especially as we can then do
printf-style formatting.

> But is it possible for the compiler to mess this up and reload msg from
> mc->error when it's about to do the user copy, so that if some other thread
> has managed to change mc->error (or is the error state sticky and no further
> operations allowed?) we'd copy from a string with a different length?

Yeah - I need to put a READ_ONCE() in there.

> Where does fs_name now get freed? vfs_fsopen doesn't seem to do it on
> success? (If it did, the fallthrough from err_mc: to err_fs_name: would
> be wrong.)

I'll add a free right after the vfs_fsopen() call before checking the error -
then I can get rid of err_fs_name.