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

[Colin King <colin.king@xxxxxxxxxxxxx>]

From: Colin Ian King <colin.king@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
---
 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