netdev_alloc_frag->page_frag_alloc may cause memory corruption in
the following process:
1. A netdev_alloc_frag function call need alloc 200 Bytes to build a skb.
2. Insufficient memory to alloc PAGE_FRAG_CACHE_MAX_ORDER(32K) in
__page_frag_cache_refill to fill frag cache, then one page(eg:4K)
is allocated, now current frag cache is 4K, alloc is success,
nc->pagecnt_bias--.
3. Then this 200 bytes skb in step 1 is freed, page->_refcount--.
4. Another netdev_alloc_frag function call need alloc 5k, page->_refcount
is equal to nc->pagecnt_bias, reset page count bias and offset to
start of new frag. page_frag_alloc will return the 4K memory for a
5K memory request.
5. The caller write on the extra 1k memory which is not actual allocated
will cause memory corruption.
page_frag_alloc is for fragmented allocation. We should warn the caller
to avoid memory corruption.
Signed-off-by: Chen Lin <chen45464546@xxxxxxx>
---
mm/page_alloc.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e008a3d..6c0db52 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5574,6 +5574,11 @@ void *page_frag_alloc_align(struct page_frag_cache *nc,
struct page *page;
int offset;
+ /* frag_alloc is not suitable for memory alloc which fragsz
+ * is bigger than PAGE_SIZE, use kmalloc or alloc_pages instead.
+ */
+ WARN_ON(fragsz > PAGE_SIZE);
+
if (unlikely(!nc->va)) {
refill:
page = __page_frag_cache_refill(nc, gfp_mask);
--
1.7.9.5
