Messages in this thread Patch in this message | | | From | Chen Lin <> | Subject | [PATCH v3] mm: page_frag: Warn_on when frag_alloc size is bigger than PAGE_SIZE | Date | Tue, 31 May 2022 22:43:08 +0800 |
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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.
When fragsz is larger than one page, we report the failure and return. I don't think it is a good idea to make efforts to support the allocation of more than one page in this function because the total frag cache size(PAGE_FRAG_CACHE_MAX_SIZE 32768) is relatively small. When the request is larger than one page, the caller should switch to use other kernel interfaces, such as kmalloc and alloc_Pages.
This bug is mainly caused by the reuse of the previously allocated frag cache memory by the following LARGER allocations. This bug existed before page_frag_alloc was ported from __netdev_alloc_frag in net/core/skbuff.c, so most Linux versions have this problem.
Signed-off-by: Chen Lin <chen45464546@163.com> --- mm/page_alloc.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index e008a3d..ffc42b5 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5574,6 +5574,15 @@ 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. + */ + if (WARN_ONCE(fragz > PAGE_SIZE, + "alloc fragsz(%d) > PAGE_SIZE(%ld) not supported, alloc fail\n", + fragsz, PAGE_SIZE)) + return NULL; + if (unlikely(!nc->va)) { refill: page = __page_frag_cache_refill(nc, gfp_mask); -- 1.7.9.5
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