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.
V3: add a comment to explain why we return NULL.
Signed-off-by: Maurizio Lombardi <mlombard@xxxxxxxxxx>
---
mm/page_alloc.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e008a3df0485..59c4dddf379f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5617,6 +5617,18 @@ 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)) {
+ /*
+ * The caller is trying to allocate a fragment
+ * with fragsz > PAGE_SIZE but the cache isn't big
+ * enough to satisfy the request, this may
+ * happen in low memory conditions.
+ * We don't release the cache page because
+ * it could make memory pressure worse
+ * so we simply return NULL here.
+ */
+ return NULL;
+ }
}
nc->pagecnt_bias--;
--
2.31.1
