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

To: Colin King <colin.king@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs: fix null pointer dereference when mapping is NULL
From: Brian Foster <bfoster@xxxxxxxxxx>
Date: Thu, 3 Sep 2015 06:45:37 -0400
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1441274260-10120-1-git-send-email-colin.king@xxxxxxxxxxxxx>
References: <1441274260-10120-1-git-send-email-colin.king@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.23 (2014-03-12)
On Thu, Sep 03, 2015 at 10:57:40AM +0100, Colin King wrote:
> 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>
> ---

Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>

>  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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