Re: [PATCH] xfs: fix invalid pointer dereference in xfs_attr3_node_inactive

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On Tue, Feb 04, 2020 at 03:06:36PM +0800, Zorro Lang wrote:
> This patch fixes below KASAN report. The xfs_attr3_node_inactive()
> gets 'child_bp' at there:
>   error = xfs_trans_get_buf(*trans, mp->m_ddev_targp,
>                             child_blkno,
>                             XFS_FSB_TO_BB(mp, mp->m_attr_geo->fsbcount), 0,
>                             &child_bp);
>   if (error)
>           return error;
>   error = bp->b_error;
> 
> But it turns to use 'bp', not 'child_bp'. And the 'bp' has been freed by:
>   xfs_trans_brelse(*trans, bp);

....
> ---
>  fs/xfs/xfs_attr_inactive.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_attr_inactive.c b/fs/xfs/xfs_attr_inactive.c
> index bbfa6ba84dcd..26230d150bf2 100644
> --- a/fs/xfs/xfs_attr_inactive.c
> +++ b/fs/xfs/xfs_attr_inactive.c
> @@ -211,7 +211,7 @@ xfs_attr3_node_inactive(
>  				&child_bp);
>  		if (error)
>  			return error;
> -		error = bp->b_error;
> +		error = child_bp->b_error;
>  		if (error) {
>  			xfs_trans_brelse(*trans, child_bp);
>  			return error;

Isn't this dead code now? i.e. any error that occurs on the buffer
during a xfs_trans_get_buf() call is returned directly and so it's
caught by the "if (error)" check. Hence this whole child_bp->b_error
check can be removed, right?

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx



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