5531 NULL pointer dereference in dsl_prop_get_ds()

Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Dan McDonald <danmcd@omniti.com>
Reviewed by: George Wilson <george@delphix.com>
Reviewed by: Bayard Bell <buffer.g.overflow@gmail.com>
Approved by: Robert Mustacchi <rm@joyent.com>

usr/src/uts/common/fs/zfs/dbuf.c

@@ -125,11 +125,9 @@ dbuf_hash(void *os, uint64_t obj, uint8_t lvl, uint64_t blkid)
 	(dbuf)->db_blkid == (blkid))
 
 dmu_buf_impl_t *
-dbuf_find(dnode_t *dn, uint8_t level, uint64_t blkid)
+dbuf_find(objset_t *os, uint64_t obj, uint8_t level, uint64_t blkid)
 {
 	dbuf_hash_table_t *h = &dbuf_hash_table;
-	objset_t *os = dn->dn_objset;
-	uint64_t obj = dn->dn_object;
 	uint64_t hv = DBUF_HASH(os, obj, level, blkid);
 	uint64_t idx = hv & h->hash_table_mask;
 	dmu_buf_impl_t *db;
@@ -149,6 +147,24 @@ dbuf_find(dnode_t *dn, uint8_t level, uint64_t blkid)
 	return (NULL);
 }
 
+static dmu_buf_impl_t *
+dbuf_find_bonus(objset_t *os, uint64_t object)
+{
+	dnode_t *dn;
+	dmu_buf_impl_t *db = NULL;
+
+	if (dnode_hold(os, object, FTAG, &dn) == 0) {
+		rw_enter(&dn->dn_struct_rwlock, RW_READER);
+		if (dn->dn_bonus != NULL) {
+			db = dn->dn_bonus;
+			mutex_enter(&db->db_mtx);
+		}
+		rw_exit(&dn->dn_struct_rwlock);
+		dnode_rele(dn, FTAG);
+	}
+	return (db);
+}
+
 /*
  * Insert an entry into the hash table.  If there is already an element
  * equal to elem in the hash table, then the already existing element
@@ -1925,7 +1941,7 @@ dbuf_prefetch(dnode_t *dn, uint64_t blkid, zio_priority_t prio)
 		return;
 
 	/* dbuf_find() returns with db_mtx held */
-	if (db = dbuf_find(dn, 0, blkid)) {
+	if (db = dbuf_find(dn->dn_objset, dn->dn_object, 0, blkid)) {
 		/*
 		 * This dbuf is already in the cache.  We assume that
 		 * it is already CACHED, or else about to be either
@@ -1972,7 +1988,7 @@ dbuf_hold_impl(dnode_t *dn, uint8_t level, uint64_t blkid, int fail_sparse,
 	*dbp = NULL;
 top:
 	/* dbuf_find() returns with db_mtx held */
-	db = dbuf_find(dn, level, blkid);
+	db = dbuf_find(dn->dn_objset, dn->dn_object, level, blkid);
 
 	if (db == NULL) {
 		blkptr_t *bp = NULL;
@@ -2108,6 +2124,30 @@ dbuf_add_ref(dmu_buf_impl_t *db, void *tag)
 	ASSERT(holds > 1);
 }
 
+#pragma weak dmu_buf_try_add_ref = dbuf_try_add_ref
+boolean_t
+dbuf_try_add_ref(dmu_buf_t *db_fake, objset_t *os, uint64_t obj, uint64_t blkid,
+    void *tag)
+{
+	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
+	dmu_buf_impl_t *found_db;
+	boolean_t result = B_FALSE;
+
+	if (db->db_blkid == DMU_BONUS_BLKID)
+		found_db = dbuf_find_bonus(os, obj);
+	else
+		found_db = dbuf_find(os, obj, 0, blkid);
+
+	if (found_db != NULL) {
+		if (db == found_db && dbuf_refcount(db) > db->db_dirtycnt) {
+			(void) refcount_add(&db->db_holds, tag);
+			result = B_TRUE;
+		}
+		mutex_exit(&db->db_mtx);
+	}
+	return (result);
+}
+
 /*
  * If you call dbuf_rele() you had better not be referencing the dnode handle
  * unless you have some other direct or indirect hold on the dnode. (An indirect

usr/src/uts/common/fs/zfs/dnode_sync.c

@@ -77,7 +77,8 @@ dnode_increase_indirection(dnode_t *dn, dmu_tx_t *tx)
 
 	/* set dbuf's parent pointers to new indirect buf */
 	for (i = 0; i < nblkptr; i++) {
-		dmu_buf_impl_t *child = dbuf_find(dn, old_toplvl, i);
+		dmu_buf_impl_t *child =
+		    dbuf_find(dn->dn_objset, dn->dn_object, old_toplvl, i);
 
 		if (child == NULL)
 			continue;

usr/src/uts/common/fs/zfs/dsl_dataset.c

@@ -360,6 +360,13 @@ dsl_dataset_snap_remove(dsl_dataset_t *ds, const char *name, dmu_tx_t *tx,
 	return (err);
 }
 
+boolean_t
+dsl_dataset_try_add_ref(dsl_pool_t *dp, dsl_dataset_t *ds, void *tag)
+{
+	return (dmu_buf_try_add_ref(ds->ds_dbuf, dp->dp_meta_objset,
+	    ds->ds_object, DMU_BONUS_BLKID, tag));
+}
+
 int
 dsl_dataset_hold_obj(dsl_pool_t *dp, uint64_t dsobj, void *tag,
     dsl_dataset_t **dsp)

usr/src/uts/common/fs/zfs/dsl_prop.c

@@ -441,9 +441,31 @@ dsl_prop_notify_all_cb(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
 	    cbr = list_next(&dd->dd_prop_cbs, cbr)) {
 		uint64_t value;
 
+		/*
+		 * Callback entries do not have holds on their datasets
+		 * so that datasets with registered callbacks are still
+		 * eligible for eviction.  Unlike operations on callbacks
+		 * for a single dataset, we are performing a recursive
+		 * descent of related datasets and the calling context
+		 * for this iteration only has a dataset hold on the root.
+		 * Without a hold, the callback's pointer to the dataset
+		 * could be invalidated by eviction at any time.
+		 *
+		 * Use dsl_dataset_try_add_ref() to verify that the
+		 * dataset has not begun eviction processing and to
+		 * prevent eviction from occurring for the duration
+		 * of the callback.  If the hold attempt fails, this
+		 * object is already being evicted and the callback can
+		 * be safely ignored.
+		 */
+		if (!dsl_dataset_try_add_ref(dp, cbr->cbr_ds, FTAG))
+			continue;
+
 		if (dsl_prop_get_ds(cbr->cbr_ds, cbr->cbr_propname,
 		    sizeof (value), 1, &value, NULL) == 0)
 			cbr->cbr_func(cbr->cbr_arg, value);
+
+		dsl_dataset_rele(cbr->cbr_ds, FTAG);
 	}
 	mutex_exit(&dd->dd_lock);
 
@@ -496,19 +518,28 @@ dsl_prop_changed_notify(dsl_pool_t *dp, uint64_t ddobj,
 	mutex_enter(&dd->dd_lock);
 	for (cbr = list_head(&dd->dd_prop_cbs); cbr;
 	    cbr = list_next(&dd->dd_prop_cbs, cbr)) {
-		uint64_t propobj = dsl_dataset_phys(cbr->cbr_ds)->ds_props_obj;
+		uint64_t propobj;
 
-		if (strcmp(cbr->cbr_propname, propname) != 0)
+		/*
+		 * cbr->cbf_ds may be invalidated due to eviction,
+		 * requiring the use of dsl_dataset_try_add_ref().
+		 * See comment block in dsl_prop_notify_all_cb()
+		 * for details.
+		 */
+		if (strcmp(cbr->cbr_propname, propname) != 0 ||
+		    !dsl_dataset_try_add_ref(dp, cbr->cbr_ds, FTAG))
 			continue;
 
+		propobj = dsl_dataset_phys(cbr->cbr_ds)->ds_props_obj;
+
 		/*
-		 * If the property is set on this ds, then it is not
-		 * inherited here; don't call the callback.
+		 * If the property is not set on this ds, then it is
+		 * inherited here; call the callback.
 		 */
-		if (propobj && 0 == zap_contains(mos, propobj, propname))
-			continue;
+		if (propobj == 0 || zap_contains(mos, propobj, propname) != 0)
+			cbr->cbr_func(cbr->cbr_arg, value);
 
-		cbr->cbr_func(cbr->cbr_arg, value);
+		dsl_dataset_rele(cbr->cbr_ds, FTAG);
 	}
 	mutex_exit(&dd->dd_lock);
 

usr/src/uts/common/fs/zfs/sys/dbuf.h

@@ -264,12 +264,15 @@ int dbuf_hold_impl(struct dnode *dn, uint8_t level, uint64_t blkid, int create,
 void dbuf_prefetch(struct dnode *dn, uint64_t blkid, zio_priority_t prio);
 
 void dbuf_add_ref(dmu_buf_impl_t *db, void *tag);
+boolean_t dbuf_try_add_ref(dmu_buf_t *db, objset_t *os, uint64_t obj,
+    uint64_t blkid, void *tag);
 uint64_t dbuf_refcount(dmu_buf_impl_t *db);
 
 void dbuf_rele(dmu_buf_impl_t *db, void *tag);
 void dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag);
 
-dmu_buf_impl_t *dbuf_find(struct dnode *dn, uint8_t level, uint64_t blkid);
+dmu_buf_impl_t *dbuf_find(struct objset *os, uint64_t object, uint8_t level,
+    uint64_t blkid);
 
 int dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags);
 void dmu_buf_will_not_fill(dmu_buf_t *db, dmu_tx_t *tx);

usr/src/uts/common/fs/zfs/sys/dmu.h

@@ -457,7 +457,23 @@ int dmu_spill_hold_existing(dmu_buf_t *bonus, void *tag, dmu_buf_t **dbp);
  */
 int dmu_buf_hold(objset_t *os, uint64_t object, uint64_t offset,
     void *tag, dmu_buf_t **, int flags);
+
+/*
+ * Add a reference to a dmu buffer that has already been held via
+ * dmu_buf_hold() in the current context.
+ */
 void dmu_buf_add_ref(dmu_buf_t *db, void* tag);
+
+/*
+ * Attempt to add a reference to a dmu buffer that is in an unknown state,
+ * using a pointer that may have been invalidated by eviction processing.
+ * The request will succeed if the passed in dbuf still represents the
+ * same os/object/blkid, is ineligible for eviction, and has at least
+ * one hold by a user other than the syncer.
+ */
+boolean_t dmu_buf_try_add_ref(dmu_buf_t *, objset_t *os, uint64_t object,
+    uint64_t blkid, void *tag);
+
 void dmu_buf_rele(dmu_buf_t *db, void *tag);
 uint64_t dmu_buf_refcount(dmu_buf_t *db);
 

usr/src/uts/common/fs/zfs/sys/dsl_dataset.h

@@ -206,6 +206,8 @@ dsl_dataset_phys(dsl_dataset_t *ds)
 
 int dsl_dataset_hold(struct dsl_pool *dp, const char *name, void *tag,
     dsl_dataset_t **dsp);
+boolean_t dsl_dataset_try_add_ref(struct dsl_pool *dp, dsl_dataset_t *ds,
+    void *tag);
 int dsl_dataset_hold_obj(struct dsl_pool *dp, uint64_t dsobj, void *tag,
     dsl_dataset_t **);
 void dsl_dataset_rele(dsl_dataset_t *ds, void *tag);