On Wed, Jul 13, 2022 at 8:01 AM 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. > > V2: do not free the cache page because this could make memory pressure > even worse, just return NULL. > > Signed-off-by: Maurizio Lombardi <mlombard@xxxxxxxxxx> > --- > mm/page_alloc.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index e008a3df0485..b1407254a826 100644 > --- 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--; This works for me. If I am not mistaken it should be only adding one conditional jump that isn't taken to the fast path based on a calculation we were already doing. Reviewed-by: Alexander Duyck <alexanderduyck@xxxxxx>
