Fix 'zfs recv' of non large_dnode send streams

Currently, there is a bug where older send streams without the
DMU_BACKUP_FEATURE_LARGE_DNODE flag are not handled correctly.
The code in receive_object() fails to handle cases where
drro->drr_dn_slots is set to 0, which is always the case when the
sending code does not support this feature flag. This patch fixes
the issue by ensuring that that a value of 0 is treated as
DNODE_MIN_SLOTS.

Tested-by:  DHE <git@dehacked.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Closes openzfs#7617
Closes openzfs#7662

module/zfs/dmu_object.c

@@ -261,6 +261,9 @@ dmu_object_reclaim_dnsize(objset_t *os, uint64_t object, dmu_object_type_t ot,
 	int dn_slots = dnodesize >> DNODE_SHIFT;
 	int err;
 
+	if (dn_slots == 0)
+		dn_slots = DNODE_MIN_SLOTS;
+
 	if (object == DMU_META_DNODE_OBJECT)
 		return (SET_ERROR(EBADF));
 

module/zfs/dmu_send.c

@@ -2139,6 +2139,8 @@ receive_object(struct receive_writer_arg *rwa, struct drr_object *drro,
 	dmu_tx_t *tx;
 	uint64_t object;
 	int err;
+	uint8_t dn_slots = drro->drr_dn_slots != 0 ?
+	    drro->drr_dn_slots : DNODE_MIN_SLOTS;
 
 	if (drro->drr_type == DMU_OT_NONE ||
 	    !DMU_OT_IS_VALID(drro->drr_type) ||
@@ -2150,7 +2152,7 @@ receive_object(struct receive_writer_arg *rwa, struct drr_object *drro,
 	    drro->drr_blksz > spa_maxblocksize(dmu_objset_spa(rwa->os)) ||
 	    drro->drr_bonuslen >
 	    DN_BONUS_SIZE(spa_maxdnodesize(dmu_objset_spa(rwa->os))) ||
-	    drro->drr_dn_slots >
+	    dn_slots >
 	    (spa_maxdnodesize(dmu_objset_spa(rwa->os)) >> DNODE_SHIFT))  {
 		return (SET_ERROR(EINVAL));
 	}
@@ -2177,7 +2179,7 @@ receive_object(struct receive_writer_arg *rwa, struct drr_object *drro,
 
 		if (drro->drr_blksz != doi.doi_data_block_size ||
 		    nblkptr < doi.doi_nblkptr ||
-		    drro->drr_dn_slots != doi.doi_dnodesize >> DNODE_SHIFT) {
+		    dn_slots != doi.doi_dnodesize >> DNODE_SHIFT) {
 			err = dmu_free_long_range(rwa->os, drro->drr_object,
 			    0, DMU_OBJECT_END);
 			if (err != 0)
@@ -2204,9 +2206,9 @@ receive_object(struct receive_writer_arg *rwa, struct drr_object *drro,
 	 * another object from the previous snapshot. We must free
 	 * these objects before we attempt to allocate the new dnode.
 	 */
-	if (drro->drr_dn_slots > 1) {
+	if (dn_slots > 1) {
 		for (uint64_t slot = drro->drr_object + 1;
-		    slot < drro->drr_object + drro->drr_dn_slots;
+		    slot < drro->drr_object + dn_slots;
 		    slot++) {
 			dmu_object_info_t slot_doi;
 
@@ -2238,7 +2240,7 @@ receive_object(struct receive_writer_arg *rwa, struct drr_object *drro,
 		err = dmu_object_claim_dnsize(rwa->os, drro->drr_object,
 		    drro->drr_type, drro->drr_blksz,
 		    drro->drr_bonustype, drro->drr_bonuslen,
-		    drro->drr_dn_slots << DNODE_SHIFT, tx);
+		    dn_slots << DNODE_SHIFT, tx);
 	} else if (drro->drr_type != doi.doi_type ||
 	    drro->drr_blksz != doi.doi_data_block_size ||
 	    drro->drr_bonustype != doi.doi_bonus_type ||
@@ -2247,7 +2249,7 @@ receive_object(struct receive_writer_arg *rwa, struct drr_object *drro,
 		err = dmu_object_reclaim_dnsize(rwa->os, drro->drr_object,
 		    drro->drr_type, drro->drr_blksz,
 		    drro->drr_bonustype, drro->drr_bonuslen,
-		    drro->drr_dn_slots << DNODE_SHIFT, tx);
+		    dn_slots << DNODE_SHIFT, tx);
 	}
 	if (err != 0) {
 		dmu_tx_commit(tx);