Messages in this thread | | | Date | Thu, 14 Jul 2022 18:04:18 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] mm: fix use-after free of page_ext after race with memory-offline |
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On Thu, 14 Jul 2022 20:17:43 +0530 Charan Teja Kalla <quic_charante@quicinc.com> wrote:
> The below is one path where race between page_ext and offline of the > respective memory blocks will cause use-after-free on the access of > page_ext structure. > > ... > > --- a/include/linux/page_ext.h > +++ b/include/linux/page_ext.h > @@ -64,6 +64,25 @@ static inline struct page_ext *page_ext_next(struct page_ext *curr) > return next; > } > > +static inline struct page_ext *get_page_ext(struct page *page) > +{ > + struct page_ext *page_ext; > + > + rcu_read_lock();
If page_ext.h is to call rcu functions then it will need to include appropriate header files.
> + page_ext = lookup_page_ext(page); > + if (!page_ext) { > + rcu_read_unlock(); > + return NULL; > + } > + > + return page_ext; > +} > + > +static inline void put_page_ext(void) > +{ > + rcu_read_unlock(); > +}
Better names would be page_ext_get() and page_ext_put(). The rest of the page_ext API appears to have got this right, so let's not mess that up.
Also, these aren't really get and put functions - page_ext doesn't have a refcount. But I can't immediately think of a name that better communicates what we're doing here so I guess get and put will do.
And are we able to add some comments here explaining why these functions exist and what they do?
> #else /* !CONFIG_PAGE_EXTENSION */ > struct page_ext;
Are you sure we didn't need CONFIG_PAGE_EXTENSION=n stubs for these two functions?
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