linux-kernel - [PATCHv2 1/2] mm/gup: fix omission of check on FOLL_LONGTERM in get_user_pages

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Message-Id: <1559543653-13185-1-git-send-email-kernelfans@gmail.com>
Date:   Mon,  3 Jun 2019 14:34:12 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     linux-mm@...ck.org
Cc:     Pingfan Liu <kernelfans@...il.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Matthew Wilcox <willy@...radead.org>,
        John Hubbard <jhubbard@...dia.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Keith Busch <keith.busch@...el.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCHv2 1/2] mm/gup: fix omission of check on FOLL_LONGTERM in get_user_pages_fast()

As for FOLL_LONGTERM, it is checked in the slow path
__gup_longterm_unlocked(). But it is not checked in the fast path, which
means a possible leak of CMA page to longterm pinned requirement through
this crack.

Place a check in the fast path.

Signed-off-by: Pingfan Liu <kernelfans@...il.com>
Cc: Ira Weiny <ira.weiny@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Mike Rapoport <rppt@...ux.ibm.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: John Hubbard <jhubbard@...dia.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Cc: Keith Busch <keith.busch@...el.com>
Cc: linux-kernel@...r.kernel.org
---
 mm/gup.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index f173fcb..6fe2feb 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2196,6 +2196,29 @@ static int __gup_longterm_unlocked(unsigned long start, int nr_pages,
 	return ret;
 }
 
+#if defined(CONFIG_CMA)
+static inline int reject_cma_pages(int nr_pinned, unsigned int gup_flags,
+	struct page **pages)
+{
+	if (unlikely(gup_flags & FOLL_LONGTERM)) {
+		int i = 0;
+
+		for (i = 0; i < nr_pinned; i++)
+			if (is_migrate_cma_page(pages[i])) {
+				put_user_pages(pages + i, nr_pinned - i);
+				return i;
+			}
+	}
+	return nr_pinned;
+}
+#else
+static inline int reject_cma_pages(int nr_pinned, unsigned int gup_flags,
+	struct page **pages)
+{
+	return nr_pinned;
+}
+#endif
+
 /**
  * get_user_pages_fast() - pin user pages in memory
  * @start:	starting user address
@@ -2236,6 +2259,7 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
 		ret = nr;
 	}
 
+	nr = reject_cma_pages(nr, gup_flags, pages);
 	if (nr < nr_pages) {
 		/* Try to get the remaining pages with get_user_pages */
 		start += nr << PAGE_SHIFT;
-- 
2.7.5