xfs: check the uniqueness of the AGFL entries

Make sure we don't list a block twice in the agfl by copying the
contents of the AGFL to an array, sorting it, and looking for
duplicates.  We can easily check that the number of agfl entries we see
actually matches the flcount, so do that too.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

fs/xfs/scrub/agheader.c

@@ -476,6 +476,12 @@ xfs_scrub_agf(
 
 /* AGFL */
 
+struct xfs_scrub_agfl_info {
+	unsigned int			sz_entries;
+	unsigned int			nr_entries;
+	xfs_agblock_t			*entries;
+};
+
 /* Scrub an AGFL block. */
 STATIC int
 xfs_scrub_agfl_block(
@@ -484,20 +490,39 @@ xfs_scrub_agfl_block(
 	void				*priv)
 {
 	struct xfs_mount		*mp = sc->mp;
+	struct xfs_scrub_agfl_info	*sai = priv;
 	xfs_agnumber_t			agno = sc->sa.agno;
 
-	if (!xfs_verify_agbno(mp, agno, agbno))
+	if (xfs_verify_agbno(mp, agno, agbno) &&
+	    sai->nr_entries < sai->sz_entries)
+		sai->entries[sai->nr_entries++] = agbno;
+	else
 		xfs_scrub_block_set_corrupt(sc, sc->sa.agfl_bp);
 
 	return 0;
 }
 
+static int
+xfs_scrub_agblock_cmp(
+	const void		*pa,
+	const void		*pb)
+{
+	const xfs_agblock_t	*a = pa;
+	const xfs_agblock_t	*b = pb;
+
+	return (int)*a - (int)*b;
+}
+
 /* Scrub the AGFL. */
 int
 xfs_scrub_agfl(
 	struct xfs_scrub_context	*sc)
 {
+	struct xfs_scrub_agfl_info	sai = { 0 };
+	struct xfs_agf			*agf;
 	xfs_agnumber_t			agno;
+	unsigned int			agflcount;
+	unsigned int			i;
 	int				error;
 
 	agno = sc->sa.agno = sc->sm->sm_agno;
@@ -508,8 +533,42 @@ xfs_scrub_agfl(
 	if (!sc->sa.agf_bp)
 		return -EFSCORRUPTED;
 
+	/* Allocate buffer to ensure uniqueness of AGFL entries. */
+	agf = XFS_BUF_TO_AGF(sc->sa.agf_bp);
+	agflcount = be32_to_cpu(agf->agf_flcount);
+	if (agflcount > XFS_AGFL_SIZE(sc->mp)) {
+		xfs_scrub_block_set_corrupt(sc, sc->sa.agf_bp);
+		goto out;
+	}
+	sai.sz_entries = agflcount;
+	sai.entries = kmem_zalloc(sizeof(xfs_agblock_t) * agflcount, KM_NOFS);
+	if (!sai.entries) {
+		error = -ENOMEM;
+		goto out;
+	}
+
 	/* Check the blocks in the AGFL. */
-	return xfs_scrub_walk_agfl(sc, xfs_scrub_agfl_block, NULL);
+	error = xfs_scrub_walk_agfl(sc, xfs_scrub_agfl_block, &sai);
+	if (error)
+		goto out_free;
+
+	if (agflcount != sai.nr_entries) {
+		xfs_scrub_block_set_corrupt(sc, sc->sa.agf_bp);
+		goto out_free;
+	}
+
+	/* Sort entries, check for duplicates. */
+	sort(sai.entries, sai.nr_entries, sizeof(sai.entries[0]),
+			xfs_scrub_agblock_cmp, NULL);
+	for (i = 1; i < sai.nr_entries; i++) {
+		if (sai.entries[i] == sai.entries[i - 1]) {
+			xfs_scrub_block_set_corrupt(sc, sc->sa.agf_bp);
+			break;
+		}
+	}
+
+out_free:
+	kmem_free(sai.entries);
 out:
 	return error;
 }