On Wed, 13 Jul 2022 17:01:43 +0200 Maurizio Lombardi <mlombard@xxxxxxxxxx> wrote: > A number of drivers call page_frag_alloc() with a > fragment's size > PAGE_SIZE. > In low memory conditions, __page_frag_cache_refill() may fail the order 3 > cache allocation and fall back to order 0; > In this case, the cache will be smaller than the fragment, causing > memory corruptions. > > Prevent this from happening by checking if the newly allocated cache > is large enough for the fragment; if not, the allocation will fail > and page_frag_alloc() will return NULL. > > ... > > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5617,6 +5617,8 @@ void *page_frag_alloc_align(struct page_frag_cache *nc, > /* reset page count bias and offset to start of new frag */ > nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1; > offset = size - fragsz; > + if (unlikely(offset < 0)) > + return NULL; > } > > nc->pagecnt_bias--; I think we should have a comment here explaining (at least) why we'd bale after a successful allocation and explaining why we don't call free_the_page().
