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

[Brian Foster]

On Thu, Sep 03, 2015 at 10:57:40AM +0100, Colin King wrote:
> From: Colin Ian King <colin.king at canonical.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 at canonical.com>
> ---

Reviewed-by: Brian Foster <bfoster at redhat.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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