Re: [PATCH] xfs: fix unreachable BIGTIME check in dquot flush validation

[Darrick J. Wong]

[fix some addresses]

On Wed, Jun 03, 2026 at 08:41:47PM +0000, Alexey Nepomnyashih wrote:
> The dqp->q_id == 0 check inside the XFS_DQTYPE_BIGTIME block is
> unreachable because root dquots return successfully earlier. Reject root
> dquots with XFS_DQTYPE_BIGTIME before that early return, preserving the
> intended validation and removing the unreachable condition.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: 4ea1ff3b4968 ("xfs: widen ondisk quota expiration timestamps to handle y2038+")
> Cc: stable@xxxxxxxxxxxxxxx # v5.10+
> Signed-off-by: Alexey Nepomnyashih <sdl@xxxxxxxx>

Yeah, that looks like a screwup...
Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>

--D

> ---
>  fs/xfs/xfs_dquot.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c
> index 69e9bc588c8b..c311f61d9554 100644
> --- a/fs/xfs/xfs_dquot.c
> +++ b/fs/xfs/xfs_dquot.c
> @@ -1216,6 +1216,14 @@ xfs_qm_dqflush_check(
>  	    type != XFS_DQTYPE_PROJ)
>  		return __this_address;
>  
> +	/* bigtime flag should never be set on root dquots */
> +	if (dqp->q_type & XFS_DQTYPE_BIGTIME) {
> +		if (!xfs_has_bigtime(dqp->q_mount))
> +			return __this_address;
> +		if (dqp->q_id == 0)
> +			return __this_address;
> +	}
> +
>  	if (dqp->q_id == 0)
>  		return NULL;
>  
> @@ -1231,14 +1239,6 @@ xfs_qm_dqflush_check(
>  	    !dqp->q_rtb.timer)
>  		return __this_address;
>  
> -	/* bigtime flag should never be set on root dquots */
> -	if (dqp->q_type & XFS_DQTYPE_BIGTIME) {
> -		if (!xfs_has_bigtime(dqp->q_mount))
> -			return __this_address;
> -		if (dqp->q_id == 0)
> -			return __this_address;
> -	}
> -
>  	return NULL;
>  }
>  
> -- 
> 2.43.0
> 
>