linux-kernel - Re: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from atomic_t to refcount

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Date:   Tue, 21 Feb 2017 08:36:25 -0800
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Elena Reshetova <elena.reshetova@...el.com>
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        peterz@...radead.org, gregkh@...uxfoundation.org,
        Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: Re: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from
 atomic_t to refcount_t

On Tue, Feb 21, 2017 at 05:49:01PM +0200, Elena Reshetova wrote:
> refcount_t type and corresponding API should be
> used instead of atomic_t when the variable is used as
> a reference counter. This allows to avoid accidental
> refcounter overflows that might lead to use-after-free
> situations.
> 
> Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
> Signed-off-by: Hans Liljestrand <ishkamiel@...il.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> Signed-off-by: David Windsor <dwindsor@...il.com>
> ---
>  fs/xfs/xfs_bmap_item.c | 4 ++--
>  fs/xfs/xfs_bmap_item.h | 4 +++-
>  2 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/xfs/xfs_bmap_item.c b/fs/xfs/xfs_bmap_item.c
> index 9bf57c7..33104ad 100644
> --- a/fs/xfs/xfs_bmap_item.c
> +++ b/fs/xfs/xfs_bmap_item.c
> @@ -199,7 +199,7 @@ xfs_bui_init(
>  	buip->bui_format.bui_nextents = XFS_BUI_MAX_FAST_EXTENTS;
>  	buip->bui_format.bui_id = (uintptr_t)(void *)buip;
>  	atomic_set(&buip->bui_next_extent, 0);
> -	atomic_set(&buip->bui_refcount, 2);
> +	refcount_set(&buip->bui_refcount, 2);
>  
>  	return buip;
>  }
> @@ -215,7 +215,7 @@ void
>  xfs_bui_release(
>  	struct xfs_bui_log_item	*buip)
>  {
> -	if (atomic_dec_and_test(&buip->bui_refcount)) {
> +	if (refcount_dec_and_test(&buip->bui_refcount)) {
>  		xfs_trans_ail_remove(&buip->bui_item, SHUTDOWN_LOG_IO_ERROR);
>  		xfs_bui_item_free(buip);
>  	}
> diff --git a/fs/xfs/xfs_bmap_item.h b/fs/xfs/xfs_bmap_item.h
> index c867daa..988a6ae 100644
> --- a/fs/xfs/xfs_bmap_item.h
> +++ b/fs/xfs/xfs_bmap_item.h
> @@ -20,6 +20,8 @@
>  #ifndef	__XFS_BMAP_ITEM_H__
>  #define	__XFS_BMAP_ITEM_H__
>  
> +#include <linux/refcount.h>

Seeing as you're sprinkling refcount_t all over XFS, this ought to go in
xfs_linux.h with all the other Linux-specific #includes.

--D

> +
>  /*
>   * There are (currently) two pairs of bmap btree redo item types: map & unmap.
>   * The common abbreviations for these are BUI (bmap update intent) and BUD
> @@ -61,7 +63,7 @@ struct kmem_zone;
>   */
>  struct xfs_bui_log_item {
>  	struct xfs_log_item		bui_item;
> -	atomic_t			bui_refcount;
> +	refcount_t			bui_refcount;
>  	atomic_t			bui_next_extent;
>  	unsigned long			bui_flags;	/* misc flags */
>  	struct xfs_bui_log_format	bui_format;
> -- 
> 2.7.4
> 
> --
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