linux-kernel - [PATCH net] page_pool: mask the page->signature before the checking

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Date:   Thu, 5 Aug 2021 09:06:57 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     <davem@...emloft.net>, <kuba@...nel.org>
CC:     <hawk@...nel.org>, <ilias.apalodimas@...aro.org>,
        <mcroce@...rosoft.com>, <willy@...radead.org>,
        <alexander.duyck@...il.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linuxarm@...neuler.org>,
        <chenhao288@...ilicon.com>
Subject: [PATCH net] page_pool: mask the page->signature before the checking

As mentioned in commit c07aea3ef4d4 ("mm: add a signature
in struct page"):
"The page->signature field is aliased to page->lru.next and
page->compound_head."

And as the comment in page_is_pfmemalloc():
"lru.next has bit 1 set if the page is allocated from the
pfmemalloc reserves. Callers may simply overwrite it if they
do not need to preserve that information."

The page->signature is or’ed with PP_SIGNATURE when a page is
allocated in page pool, see __page_pool_alloc_pages_slow(),
and page->signature is checked directly with PP_SIGNATURE in
page_pool_return_skb_page(), which might cause resoure leaking
problem for a page from page pool if bit 1 of lru.next is set for
a pfmemalloc page.

As bit 0 is page->compound_head, So mask both bit 0 and 1 before
the checking in page_pool_return_skb_page().

Fixes: 6a5bcd84e886 ("page_pool: Allow drivers to hint on SKB recycling")
Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
---
 net/core/page_pool.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 5e4eb45..33b7dd7 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -634,7 +634,7 @@ bool page_pool_return_skb_page(struct page *page)
 	struct page_pool *pp;

 	page = compound_head(page);
-	if (unlikely(page->pp_magic != PP_SIGNATURE))
+	if (unlikely((page->pp_magic & ~0x3UL) != PP_SIGNATURE))
 		return false;

 	pp = page->pp;
-- 
2.7.4