linux-kernel - Re: [PATCH 1/1] mm: implement ->map

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Date:	Mon,  3 Mar 2014 13:07:46 +0200 (EET)
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Ning Qu <quning@...gle.com>, Hugh Dickins <hughd@...gle.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Dave Chinner <david@...morbit.com>, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mm: implement ->map_pages for shmem/tmpfs

Ning Qu wrote:
> Btw, should we first check if page returned by radix_tree_deref_slot is NULL?

Yes, we should. I don't know how I missed that. :(

The patch below should address both issues.

>From dca24c9a1f31ee1599fe81e9a60d4f87a4eaf0ea Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Date: Mon, 3 Mar 2014 12:07:03 +0200
Subject: [PATCH] mm: filemap_map_pages() avoid dereference NULL/exception
 slots

radix_tree_deref_slot() can return NULL: add missed check.

Do no dereference 'page': we can get there as result of
radix_tree_exception(page) check.

Reported-by: Hugh Dickins <hughd@...gle.com>
Reported-by: Ning Qu <quning@...gle.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 mm/filemap.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 5f4fe7f0c258..e48624634927 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1745,6 +1745,8 @@ void filemap_map_pages(struct vm_area_struct *vma, struct vm_fault *vmf)
 			break;
 repeat:
 		page = radix_tree_deref_slot(slot);
+		if (unlikely(!page))
+			goto next;
 		if (radix_tree_exception(page)) {
 			if (radix_tree_deref_retry(page))
 				break;
@@ -1790,7 +1792,7 @@ unlock:
 skip:
 		page_cache_release(page);
 next:
-		if (page->index == vmf->max_pgoff)
+		if (iter.index == vmf->max_pgoff)
 			break;
 	}
 	rcu_read_unlock();
-- 
 Kirill A. Shutemov
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