Re:[PATCH v2] mm/codetag: move tag retrieval back upfront in __free_pages()

David Wang
2025-05-05T19:18:16Z

Sorry, I made a mistake, pgalloc_tag_get should have a dummy definition
when CONFIG_MEM_ALLOC_PROFILING not defined, will send another patch.

At 2025-05-06 02:34:23, "David Wang" <00107082@163.com> wrote:
>Commit 51ff4d7486f0 ("mm: avoid extra mem_alloc_profiling_enabled()
> checks") introduces a possible use-after-free scenario, when page
>is non-compound, page[0] could be released by other thread right
>after put_page_testzero failed in current thread, pgalloc_tag_sub_pages
>afterwards would manipulate an invalid page for accounting remaining
>pages:
>
>[timeline] [thread1] [thread2]
> | alloc_page non-compound
> V
> | get_page, rf counter inc
> V
> | in ___free_pages
> | put_page_testzero fails
> V
> | put_page, page released
> V
> | in ___free_pages,
> | pgalloc_tag_sub_pages
> | manipulate an invalid page
> V
>
>Restore __free_pages() to its state before, retrieve alloc tag
>beforehand.
>
>Fixes: 51ff4d7486f0 ("mm: avoid extra mem_alloc_profiling_enabled() checks")
>Signed-off-by: David Wang <00107082@163.com>
>---
> include/linux/pgalloc_tag.h | 7 +++++++
> mm/page_alloc.c | 15 ++++++---------
> 2 files changed, 13 insertions(+), 9 deletions(-)
>
>diff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h
>index c74077977830..97eb4835568e 100644
>--- a/include/linux/pgalloc_tag.h
>+++ b/include/linux/pgalloc_tag.h
>@@ -188,6 +188,13 @@ static inline struct alloc_tag *__pgalloc_tag_get(struct page *page)
> return tag;
> }
>
>+static inline struct alloc_tag *pgalloc_tag_get(struct page *page)
>+{
>+ if (mem_alloc_profiling_enabled())
>+ return __pgalloc_tag_get(page);
>+ return NULL;
>+}
>+
> void pgalloc_tag_split(struct folio *folio, int old_order, int new_order);
> void pgalloc_tag_swap(struct folio *new, struct folio *old);
>
>diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>index 5669baf2a6fe..1b00e14a9780 100644
>--- a/mm/page_alloc.c
>+++ b/mm/page_alloc.c
>@@ -1151,14 +1151,9 @@ static inline void pgalloc_tag_sub(struct page *page, unsigned int nr)
> __pgalloc_tag_sub(page, nr);
> }
>
>-static inline void pgalloc_tag_sub_pages(struct page *page, unsigned int nr)
>+/* When tag is not NULL, assuming mem_alloc_profiling_enabled */
>+static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr)
> {
>- struct alloc_tag *tag;
>-
>- if (!mem_alloc_profiling_enabled())
>- return;
>-
>- tag = __pgalloc_tag_get(page);
> if (tag)
> this_cpu_sub(tag->counters->bytes, PAGE_SIZE * nr);
> }
>@@ -1168,7 +1163,7 @@ static inline void pgalloc_tag_sub_pages(struct page *page, unsigned int nr)
> static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,
> unsigned int nr) {}
> static inline void pgalloc_tag_sub(struct page *page, unsigned int nr) {}
>-static inline void pgalloc_tag_sub_pages(struct page *page, unsigned int nr) {}
>+static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr) {}
>
> #endif /* CONFIG_MEM_ALLOC_PROFILING */
>
>@@ -5065,11 +5060,13 @@ static void ___free_pages(struct page *page, unsigned int order,
> {
> /* get PageHead before we drop reference */
> int head = PageHead(page);
>+ /* get alloc tag in case the page is released by others */
>+ struct alloc_tag *tag = pgalloc_tag_get(page);
>
> if (put_page_testzero(page))
> __free_frozen_pages(page, order, fpi_flags);
> else if (!head) {
>- pgalloc_tag_sub_pages(page, (1 << order) - 1);
>+ pgalloc_tag_sub_pages(tag, (1 << order) - 1);
> while (order-- > 0)
> __free_frozen_pages(page + (1 << order), order,
> fpi_flags);
>--
>2.39.2