[PATCH 07/21] NFSv4/flexfiles: Hold a device node reference for layoutstats encoding

ff_layout_mirror_prepare_stats() records a stripe's device under i_lock,
but the layoutstats/layoutreturn XDR encode runs later and dereferences
the mirror's pinned device node (for the DS netaddr) with no reference
of its own.  Once a CHANGE notification can re-point the pinned node,
that read becomes use-after-free.

Take a node reference at prepare time and carry it with the stripe in a
per-devinfo nfs4_ff_layoutstat_priv, released in
ff_layout_free_layoutstats().  The priv entries live alongside the
devinfo array: co-allocated for LAYOUTSTATS, an additional member of
nfs4_flexfile_layoutreturn_args for LAYOUTRETURN.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Benjamin Coddington <bcodding-F/[email protected]>
---
 fs/nfs/flexfilelayout/flexfilelayout.c | 53 +++++++++++++++++---------
 fs/nfs/flexfilelayout/flexfilelayout.h | 11 ++++++
 2 files changed, 47 insertions(+), 17 deletions(-)

diff --git a/fs/nfs/flexfilelayout/flexfilelayout.c b/fs/nfs/flexfilelayout/flexfilelayout.c
index b52323e639a2..c07409056292 100644
--- a/fs/nfs/flexfilelayout/flexfilelayout.c
+++ b/fs/nfs/flexfilelayout/flexfilelayout.c
@@ -44,10 +44,11 @@ static void ff_layout_read_record_layoutstats_done(struct rpc_task *task,
 static int
 ff_layout_mirror_prepare_stats(struct pnfs_layout_hdr *lo,
 			       struct nfs42_layoutstat_devinfo *devinfo,
+			       struct nfs4_ff_layoutstat_priv *priv,
 			       int dev_limit, enum nfs4_ff_op_type type);
 static void ff_layout_encode_ff_layoutupdate(struct xdr_stream *xdr,
 			      const struct nfs42_layoutstat_devinfo *devinfo,
-			      struct nfs4_ff_layout_ds_stripe *dss_info);
+			      struct nfs4_ff_layoutstat_priv *priv);
 
 static struct pnfs_layout_hdr *
 ff_layout_alloc_layout_hdr(struct inode *inode, gfp_t gfp_flags)
@@ -2703,7 +2704,7 @@ ff_layout_prepare_layoutreturn(struct nfs4_layoutreturn_args *args)
 
 	spin_lock(&args->inode->i_lock);
 	ff_args->num_dev = ff_layout_mirror_prepare_stats(
-		&ff_layout->generic_hdr, &ff_args->devinfo[0],
+		&ff_layout->generic_hdr, &ff_args->devinfo[0], &ff_args->priv[0],
 		ARRAY_SIZE(ff_args->devinfo), NFS4_FF_OP_LAYOUTRETURN);
 	spin_unlock(&args->inode->i_lock);
 
@@ -2878,10 +2879,11 @@ ff_layout_encode_io_latency(struct xdr_stream *xdr,
 static void
 ff_layout_encode_ff_layoutupdate(struct xdr_stream *xdr,
 			      const struct nfs42_layoutstat_devinfo *devinfo,
-			      struct nfs4_ff_layout_ds_stripe *dss_info)
+			      struct nfs4_ff_layoutstat_priv *priv)
 {
+	struct nfs4_ff_layout_ds_stripe *dss_info = priv->dss_info;
 	struct nfs4_pnfs_ds_addr *da;
-	struct nfs4_pnfs_ds *ds = dss_info->mirror_ds->ds;
+	struct nfs4_pnfs_ds *ds = priv->mirror_ds->ds;
 	struct nfs_fh *fh = &dss_info->fh_versions[0];
 	__be32 *p;
 
@@ -2928,10 +2930,10 @@ ff_layout_encode_layoutstats(struct xdr_stream *xdr, const void *args,
 static void
 ff_layout_free_layoutstats(struct nfs4_xdr_opaque_data *opaque)
 {
-	struct nfs4_ff_layout_ds_stripe *dss_info = opaque->data;
-	struct nfs4_ff_layout_mirror *mirror = dss_info->mirror;
+	struct nfs4_ff_layoutstat_priv *priv = opaque->data;
 
-	ff_layout_put_mirror(mirror);
+	nfs4_ff_layout_put_deviceid(priv->mirror_ds);
+	ff_layout_put_mirror(priv->dss_info->mirror);
 }
 
 static const struct nfs4_xdr_opaque_ops layoutstat_ops = {
@@ -2942,12 +2944,13 @@ static const struct nfs4_xdr_opaque_ops layoutstat_ops = {
 static int
 ff_layout_mirror_prepare_stats(struct pnfs_layout_hdr *lo,
 			       struct nfs42_layoutstat_devinfo *devinfo,
+			       struct nfs4_ff_layoutstat_priv *priv,
 			       int dev_limit, enum nfs4_ff_op_type type)
 {
 	struct nfs4_flexfile_layout *ff_layout = FF_LAYOUT_FROM_HDR(lo);
 	struct nfs4_ff_layout_mirror *mirror;
 	struct nfs4_ff_layout_ds_stripe *dss_info;
-	struct nfs4_deviceid_node *dev;
+	struct nfs4_ff_layout_ds *mirror_ds;
 	int i = 0, dss_id;
 
 	list_for_each_entry(mirror, &ff_layout->mirrors, mirrors) {
@@ -2955,7 +2958,8 @@ ff_layout_mirror_prepare_stats(struct pnfs_layout_hdr *lo,
 			dss_info = &mirror->dss[dss_id];
 			if (i >= dev_limit)
 				break;
-			if (IS_ERR_OR_NULL(dss_info->mirror_ds))
+			mirror_ds = dss_info->mirror_ds;
+			if (IS_ERR_OR_NULL(mirror_ds))
 				continue;
 			if (!test_and_clear_bit(NFS4_FF_MIRROR_STAT_AVAIL,
 						&mirror->flags) &&
@@ -2964,9 +2968,14 @@ ff_layout_mirror_prepare_stats(struct pnfs_layout_hdr *lo,
 			/* mirror refcount put in cleanup_layoutstats */
 			if (!refcount_inc_not_zero(&mirror->ref))
 				continue;
-			dev = &dss_info->mirror_ds->id_node;
+			/*
+			 * The mirror's pin holds the node while we're under
+			 * i_lock; take a reference for the encode, put in
+			 * ff_layout_free_layoutstats().
+			 */
+			atomic_inc(&mirror_ds->id_node.ref);
 			memcpy(&devinfo->dev_id,
-			       &dev->deviceid,
+			       &mirror_ds->id_node.deviceid,
 			       NFS4_DEVICEID4_SIZE);
 			devinfo->offset = 0;
 			devinfo->length = NFS4_MAX_UINT64;
@@ -2982,9 +2991,12 @@ ff_layout_mirror_prepare_stats(struct pnfs_layout_hdr *lo,
 			spin_unlock(&mirror->lock);
 			devinfo->layout_type = LAYOUT_FLEX_FILES;
 			devinfo->ld_private.ops = &layoutstat_ops;
-			devinfo->ld_private.data = &mirror->dss[dss_id];
+			priv->dss_info = dss_info;
+			priv->mirror_ds = mirror_ds;
+			devinfo->ld_private.data = priv;
 
 			devinfo++;
+			priv++;
 			i++;
 		}
 	}
@@ -2995,21 +3007,28 @@ static int ff_layout_prepare_layoutstats(struct nfs42_layoutstat_args *args)
 {
 	struct pnfs_layout_hdr *lo;
 	struct nfs4_flexfile_layout *ff_layout;
+	struct nfs4_ff_layoutstat_priv *priv;
 	const int dev_count = PNFS_LAYOUTSTATS_MAXDEV;
 
-	/* For now, send at most PNFS_LAYOUTSTATS_MAXDEV statistics */
-	args->devinfo = kmalloc_objs(*args->devinfo, dev_count,
-				     nfs_io_gfp_mask());
+	/*
+	 * For now, send at most PNFS_LAYOUTSTATS_MAXDEV statistics.
+	 * The per-devinfo private entries are co-allocated after the
+	 * devinfo array and freed along with it.
+	 */
+	args->devinfo = kmalloc(dev_count * (sizeof(*args->devinfo) +
+					     sizeof(*priv)),
+				nfs_io_gfp_mask());
 	if (!args->devinfo)
 		return -ENOMEM;
+	priv = (struct nfs4_ff_layoutstat_priv *)&args->devinfo[dev_count];
 
 	spin_lock(&args->inode->i_lock);
 	lo = NFS_I(args->inode)->layout;
 	if (lo && pnfs_layout_is_valid(lo)) {
 		ff_layout = FF_LAYOUT_FROM_HDR(lo);
 		args->num_dev = ff_layout_mirror_prepare_stats(
-			&ff_layout->generic_hdr, &args->devinfo[0], dev_count,
-			NFS4_FF_OP_LAYOUTSTATS);
+			&ff_layout->generic_hdr, &args->devinfo[0], priv,
+			dev_count, NFS4_FF_OP_LAYOUTSTATS);
 	} else
 		args->num_dev = 0;
 	spin_unlock(&args->inode->i_lock);
diff --git a/fs/nfs/flexfilelayout/flexfilelayout.h b/fs/nfs/flexfilelayout/flexfilelayout.h
index ceed1a9dd697..d6ec80cf8a6e 100644
--- a/fs/nfs/flexfilelayout/flexfilelayout.h
+++ b/fs/nfs/flexfilelayout/flexfilelayout.h
@@ -124,9 +124,20 @@ struct nfs4_flexfile_layout {
 	unsigned long		flags;
 };
 
+/*
+ * Per-devinfo private data for a layoutstats/layoutreturn encode: the
+ * stripe the stats describe plus a reference on its device node so the
+ * node (and its DS addresses) stay valid until the XDR encode runs.
+ */
+struct nfs4_ff_layoutstat_priv {
+	struct nfs4_ff_layout_ds_stripe *dss_info;
+	struct nfs4_ff_layout_ds *mirror_ds;
+};
+
 struct nfs4_flexfile_layoutreturn_args {
 	struct list_head errors;
 	struct nfs42_layoutstat_devinfo devinfo[FF_LAYOUTSTATS_MAXDEV];
+	struct nfs4_ff_layoutstat_priv priv[FF_LAYOUTSTATS_MAXDEV];
 	unsigned int num_errors;
 	unsigned int num_dev;
 	struct page *pages[1];
-- 
2.53.0