Re: [PATCH] module: print module name on refcount error

On Fri 07-07-23 11:56:49, Luis Chamberlain wrote:

On Mon, Jul 03, 2023 at 03:47:22PM +0200, Michal Hocko wrote:

quoted

On Fri 30-06-23 16:05:33, Luis Chamberlain wrote:
[...]

quoted

What prevents code from racing the free with a random module_put()
called by some other piece of code?

Wouldn't be ref count a garbage already? How can you race when freeing
if module_put fail?

It could yes, ie, so this risks at all being junk.

Could you be more specific please? I still do not see a scenario where
module string name would be junk while refcount itself would be a valid
memory.

So best IMHO is
to tidy up all the get / puts and add respective tests to fix all
this mess with proper messages as needed. My cursory review of the
refcnt stuf is I see some races possible.

It would likely be better to use refcount_t instead of atomic_t.

While I'd be happy to help debugging aids, adding accesses to random
memory for a string seems more risk prone.

If there is really a scenario when module could be unloaded leaving
dangling struct module behind then we have a real problem as this is
exported to userspace IIRC. Not to mention module_get/put calls
modifying memory (UAF).
-- 
Michal Hocko
SUSE Labs