Re: [PATCH 3/6] xfs: sanity check ag header values in xrep_calc_ag_resblks

[Allison Henderson <allison.henderson@oracle.com>]

On 08/11/2018 08:35 AM, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Check the values we read in from the AG headers when calculating the
> block reservations for a repair transaction.  If they're obviously
> wrong, substitute worst case assumptions (rather than ENOSPC on a bogus
> reservatoin request).
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>   fs/xfs/scrub/repair.c |   46 +++++++++++++++++++++++++++-------------------
>   1 file changed, 27 insertions(+), 19 deletions(-)
> 
> 
> diff --git a/fs/xfs/scrub/repair.c b/fs/xfs/scrub/repair.c
> index 42d8c798ce7d..97c3077fb005 100644
> --- a/fs/xfs/scrub/repair.c
> +++ b/fs/xfs/scrub/repair.c
> @@ -195,8 +195,8 @@ xrep_calc_ag_resblks(
>   	struct xfs_scrub_metadata	*sm = sc->sm;
>   	struct xfs_perag		*pag;
>   	struct xfs_buf			*bp;
> -	xfs_agino_t			icount = 0;
> -	xfs_extlen_t			aglen = 0;
> +	xfs_agino_t			icount = NULLAGINO;
> +	xfs_extlen_t			aglen = NULLAGBLOCK;
>   	xfs_extlen_t			usedlen;
>   	xfs_extlen_t			freelen;
>   	xfs_extlen_t			bnobt_sz;
> @@ -208,20 +208,14 @@ xrep_calc_ag_resblks(
>   	if (!(sm->sm_flags & XFS_SCRUB_IFLAG_REPAIR))
>   		return 0;
>   
> -	/* Use in-core counters if possible. */
>   	pag = xfs_perag_get(mp, sm->sm_agno);
> -	if (pag->pagi_init)
> +	if (pag->pagi_init) {
> +		/* Use in-core icount if possible. */
>   		icount = pag->pagi_count;
> -
> -	/*
> -	 * Otherwise try to get the actual counters from disk; if not, make
> -	 * some worst case assumptions.
> -	 */
> -	if (icount == 0) {
> +	} else {
> +		/* Try to get the actual counters from disk. */
>   		error = xfs_ialloc_read_agi(mp, NULL, sm->sm_agno, &bp);
> -		if (error) {
> -			icount = mp->m_sb.sb_agblocks / mp->m_sb.sb_inopblock;
> -		} else {
> +		if (!error) {
>   			icount = pag->pagi_count;
>   			xfs_buf_relse(bp);
>   		}
> @@ -229,18 +223,32 @@ xrep_calc_ag_resblks(
>   
>   	/* Now grab the block counters from the AGF. */
>   	error = xfs_alloc_read_agf(mp, NULL, sm->sm_agno, 0, &bp);
> -	if (error) {
> -		aglen = mp->m_sb.sb_agblocks;
> -		freelen = aglen;
> -		usedlen = aglen;
> -	} else {
> +	if (!error) {
>   		aglen = be32_to_cpu(XFS_BUF_TO_AGF(bp)->agf_length);
> -		freelen = pag->pagf_freeblks;
> +		freelen = be32_to_cpu(XFS_BUF_TO_AGF(bp)->agf_freeblks);
>   		usedlen = aglen - freelen;
>   		xfs_buf_relse(bp);
>   	}
>   	xfs_perag_put(pag);
>   
> +	/* If the icount is impossible, make some worst-case assumptions. */
> +	if (icount == NULLAGINO ||
> +	    !xfs_verify_agino(mp, sm->sm_agno, icount)) {
> +		xfs_agino_t	first, last;
> +
> +		xfs_agino_range(mp, sm->sm_agno, &first, &last);
> +		icount = last - first + 1;
> +	}
> +
> +	/* If the block counts are impossible, make worst-case assumptions. */
> +	if (aglen == NULLAGBLOCK ||
> +	    aglen != xfs_ag_block_count(mp, sm->sm_agno) ||
> +	    freelen >= aglen) {
> +		aglen = xfs_ag_block_count(mp, sm->sm_agno);
> +		freelen = aglen;
> +		usedlen = aglen;
> +	}
> +
>   	trace_xrep_calc_ag_resblks(mp, sm->sm_agno, icount, aglen,
>   			freelen, usedlen);
>   
> 
Ok, makes sense
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>