linux-kernel - [PATCH] xfs: fix null pointer dereference when mapping is NULL

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Message-Id: <1441274260-10120-1-git-send-email-colin.king@canonical.com>
Date:	Thu,  3 Sep 2015 10:57:40 +0100
From:	Colin King <colin.king@...onical.com>
To:	Dave Chinner <david@...morbit.com>, xfs@....sgi.com
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] xfs: fix null pointer dereference when mapping is NULL

From: Colin Ian King <colin.king@...onical.com>

xfs_vm_set_page_dirty checks to see if mapping is NULL however
before this unlikely check it already dereferenced mapping when
initializing inode. Move the inode initialization after the mapping
null check to avoid a potential null pointer dereference.

Fixes: 22e757a49cf0 ("xfs: don't dirty buffers beyond EOF")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 fs/xfs/xfs_aops.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index c77499b..d15ae85 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -1935,7 +1935,7 @@ xfs_vm_set_page_dirty(
 	struct page		*page)
 {
 	struct address_space	*mapping = page->mapping;
-	struct inode		*inode = mapping->host;
+	struct inode		*inode;
 	loff_t			end_offset;
 	loff_t			offset;
 	int			newly_dirty;
@@ -1944,6 +1944,7 @@ xfs_vm_set_page_dirty(
 	if (unlikely(!mapping))
 		return !TestSetPageDirty(page);
 
+	inode = mapping->host;
 	end_offset = i_size_read(inode);
 	offset = page_offset(page);
 
-- 
2.5.0

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