Re: [PATCH V2] Fix use-after-free with buffers

[Christoph Hellwig <hch@infradead.org>]

On Tue, Sep 02, 2008 at 04:05:15PM +1000, Lachlan McIlroy wrote:
> We have a use-after-free issue where log completions access buffers via the
> buffer log item and the buffer has already been freed.  Fix this by taking
> a reference on the buffer when attaching the buffer log item and release
> the hold when the buffer log item is detached and we no longer need the
> buffer.  Also create a new function xfs_buf_item_free() to combine some
> common code and move an ASSERT in xfs_buf_rele() so that we can catch more
> cases. 

Looks good, but please mark xfs_buf_item_free static.

>
> --- a/fs/xfs/xfs_buf_item.c	2008-09-02 15:56:20.000000000 +1000
> +++ b/fs/xfs/xfs_buf_item.c	2008-08-22 13:23:53.000000000 +1000
> @@ -732,6 +732,7 @@ xfs_buf_item_init(
> 	bip->bli_item.li_ops = &xfs_buf_item_ops;
> 	bip->bli_item.li_mountp = mp;
> 	bip->bli_buf = bp;
> +	xfs_buf_hold(bp);
> 	bip->bli_format.blf_type = XFS_LI_BUF;
> 	bip->bli_format.blf_blkno = (__int64_t)XFS_BUF_ADDR(bp);
> 	bip->bli_format.blf_len = (ushort)BTOBB(XFS_BUF_COUNT(bp));
> @@ -867,6 +868,21 @@ xfs_buf_item_dirty(
> 	return (bip->bli_flags & XFS_BLI_DIRTY);
> }
>
> +void
> +xfs_buf_item_free(
> +	xfs_buf_log_item_t	*bip)
> +{
> +#ifdef XFS_TRANS_DEBUG
> +	kmem_free(bip->bli_orig);
> +	kmem_free(bip->bli_logged);
> +#endif /* XFS_TRANS_DEBUG */
> +
> +#ifdef XFS_BLI_TRACE
> +	ktrace_free(bip->bli_trace);
> +#endif
> +	kmem_zone_free(xfs_buf_item_zone, bip);
> +}
> +
> /*
>  * This is called when the buf log item is no longer needed.  It should
>  * free the buf log item associated with the given buffer and clear
> @@ -887,18 +903,8 @@ xfs_buf_item_relse(
> 	    (XFS_BUF_IODONE_FUNC(bp) != NULL)) {
> 		XFS_BUF_CLR_IODONE_FUNC(bp);
> 	}
> -
> -#ifdef XFS_TRANS_DEBUG
> -	kmem_free(bip->bli_orig);
> -	bip->bli_orig = NULL;
> -	kmem_free(bip->bli_logged);
> -	bip->bli_logged = NULL;
> -#endif /* XFS_TRANS_DEBUG */
> -
> -#ifdef XFS_BLI_TRACE
> -	ktrace_free(bip->bli_trace);
> -#endif
> -	kmem_zone_free(xfs_buf_item_zone, bip);
> +	xfs_buf_rele(bp);
> +	xfs_buf_item_free(bip);
> }
>
>
> @@ -1120,6 +1126,7 @@ xfs_buf_iodone(
>
> 	ASSERT(bip->bli_buf == bp);
>
> +	xfs_buf_rele(bp);
> 	mp = bip->bli_item.li_mountp;
>
> 	/*
> @@ -1136,18 +1143,7 @@ xfs_buf_iodone(
> 	 * xfs_trans_delete_ail() drops the AIL lock.
> 	 */
> 	xfs_trans_delete_ail(mp, (xfs_log_item_t *)bip);
> -
> -#ifdef XFS_TRANS_DEBUG
> -	kmem_free(bip->bli_orig);
> -	bip->bli_orig = NULL;
> -	kmem_free(bip->bli_logged);
> -	bip->bli_logged = NULL;
> -#endif /* XFS_TRANS_DEBUG */
> -
> -#ifdef XFS_BLI_TRACE
> -	ktrace_free(bip->bli_trace);
> -#endif
> -	kmem_zone_free(xfs_buf_item_zone, bip);
> +	xfs_buf_item_free(bip);
> }
>
> #if defined(XFS_BLI_TRACE)
>
>
---end quoted text---