MFC r305209: MFV r302660: 6314 buffer overflow in dsl_dataset_name

illumos/illumos-gate@9adfa60d484ce2435f5af77cc99dcd4e692b6660
https://github.com/illumos/illumos-gate/commit/9adfa60d484ce2435f5af77cc99dcd4e6
92b6660

https://www.illumos.org/issues/6314
  Callers of dsl_dataset_name pass a buffer of size ZFS_MAXNAMELEN, but
  dsl_dataset_name copies the datasets' name PLUS the snapshot name to it,
  resulting in a max of 2 * ZFS_MAXNAMELEN + '@'.

Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Reviewed by: Igor Kozhukhov <ikozhukhov@gmail.com>
Approved by: Dan McDonald <danmcd@omniti.com>
Author: Matthew Ahrens <mahrens@delphix.com>

23 files changed, 134 insertions, 126 deletions

diff --git a/sys/cddl/contrib/opensolaris/common/zfs/zfs_namecheck.c b/sys/cddl/contrib/opensolaris/common/zfs/zfs_namecheck.c
index a32955f..439d449 100644
--- a/sys/cddl/contrib/opensolaris/common/zfs/zfs_namecheck.c
+++ b/sys/cddl/contrib/opensolaris/common/zfs/zfs_namecheck.c
@@ -69,7 +69,7 @@ zfs_component_namecheck(const char *path, namecheck_err_t *why, char *what)
 {
 	const char *loc;
 
-	if (strlen(path) >= MAXNAMELEN) {
+	if (strlen(path) >= ZFS_MAX_DATASET_NAME_LEN) {
 		if (why)
 			*why = NAME_ERR_TOOLONG;
 		return (-1);
@@ -140,14 +140,9 @@ dataset_namecheck(const char *path, namecheck_err_t *why, char *what)
 
 	/*
 	 * Make sure the name is not too long.
-	 *
-	 * ZFS_MAXNAMELEN is the maximum dataset length used in the userland
-	 * which is the same as MAXNAMELEN used in the kernel.
-	 * If ZFS_MAXNAMELEN value is changed, make sure to cleanup all
-	 * places using MAXNAMELEN.
 	 */
 
-	if (strlen(path) >= MAXNAMELEN) {
+	if (strlen(path) >= ZFS_MAX_DATASET_NAME_LEN) {
 		if (why)
 			*why = NAME_ERR_TOOLONG;
 		return (-1);
@@ -276,7 +271,7 @@ mountpoint_namecheck(const char *path, namecheck_err_t *why)
 		while (*end != '/' && *end != '\0')
 			end++;
 
-		if (end - start >= MAXNAMELEN) {
+		if (end - start >= ZFS_MAX_DATASET_NAME_LEN) {
 			if (why)
 				*why = NAME_ERR_TOOLONG;
 			return (-1);
@@ -301,13 +296,8 @@ pool_namecheck(const char *pool, namecheck_err_t *why, char *what)
 
 	/*
 	 * Make sure the name is not too long.
-	 *
-	 * ZPOOL_MAXNAMELEN is the maximum pool length used in the userland
-	 * which is the same as MAXNAMELEN used in the kernel.
-	 * If ZPOOL_MAXNAMELEN value is changed, make sure to cleanup all
-	 * places using MAXNAMELEN.
 	 */
-	if (strlen(pool) >= MAXNAMELEN) {
+	if (strlen(pool) >= ZFS_MAX_DATASET_NAME_LEN) {
 		if (why)
 			*why = NAME_ERR_TOOLONG;
 		return (-1);
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_objset.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_objset.c
index 82c5854..78ab962 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_objset.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_objset.c
@@ -621,7 +621,7 @@ dmu_objset_refresh_ownership(objset_t *os, void *tag)
 {
 	dsl_pool_t *dp;
 	dsl_dataset_t *ds, *newds;
-	char name[MAXNAMELEN];
+	char name[ZFS_MAX_DATASET_NAME_LEN];
 
 	ds = os->os_dsl_dataset;
 	VERIFY3P(ds, !=, NULL);
@@ -839,6 +839,9 @@ dmu_objset_create_check(void *arg, dmu_tx_t *tx)
 	if (strchr(doca->doca_name, '@') != NULL)
 		return (SET_ERROR(EINVAL));
 
+	if (strlen(doca->doca_name) >= ZFS_MAX_DATASET_NAME_LEN)
+		return (SET_ERROR(ENAMETOOLONG));
+
 	error = dsl_dir_hold(dp, doca->doca_name, FTAG, &pdd, &tail);
 	if (error != 0)
 		return (error);
@@ -923,6 +926,9 @@ dmu_objset_clone_check(void *arg, dmu_tx_t *tx)
 	if (strchr(doca->doca_clone, '@') != NULL)
 		return (SET_ERROR(EINVAL));
 
+	if (strlen(doca->doca_clone) >= ZFS_MAX_DATASET_NAME_LEN)
+		return (SET_ERROR(ENAMETOOLONG));
+
 	error = dsl_dir_hold(dp, doca->doca_clone, FTAG, &pdd, &tail);
 	if (error != 0)
 		return (error);
@@ -962,7 +968,7 @@ dmu_objset_clone_sync(void *arg, dmu_tx_t *tx)
 	const char *tail;
 	dsl_dataset_t *origin, *ds;
 	uint64_t obj;
-	char namebuf[MAXNAMELEN];
+	char namebuf[ZFS_MAX_DATASET_NAME_LEN];
 
 	VERIFY0(dsl_dir_hold(dp, doca->doca_clone, FTAG, &pdd, &tail));
 	VERIFY0(dsl_dataset_hold(dp, doca->doca_origin, FTAG, &origin));
@@ -1973,7 +1979,7 @@ dmu_objset_get_user(objset_t *os)
 
 /*
  * Determine name of filesystem, given name of snapshot.
- * buf must be at least MAXNAMELEN bytes
+ * buf must be at least ZFS_MAX_DATASET_NAME_LEN bytes
  */
 int
 dmu_fsname(const char *snapname, char *buf)
@@ -1981,7 +1987,7 @@ dmu_fsname(const char *snapname, char *buf)
 	char *atp = strchr(snapname, '@');
 	if (atp == NULL)
 		return (SET_ERROR(EINVAL));
-	if (atp - snapname >= MAXNAMELEN)
+	if (atp - snapname >= ZFS_MAX_DATASET_NAME_LEN)
 		return (SET_ERROR(ENAMETOOLONG));
 	(void) strlcpy(buf, snapname, atp - snapname + 1);
 	return (0);
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_send.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_send.c
index 9e8d86e..874a1ca 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_send.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_send.c
@@ -1347,7 +1347,7 @@ dmu_recv_begin_check(void *arg, dmu_tx_t *tx)
 		dsl_dataset_rele(ds, FTAG);
 	} else if (error == ENOENT) {
 		/* target fs does not exist; must be a full backup or clone */
-		char buf[MAXNAMELEN];
+		char buf[ZFS_MAX_DATASET_NAME_LEN];
 
 		/*
 		 * If it's a non-clone incremental, we are missing the
@@ -1367,7 +1367,7 @@ dmu_recv_begin_check(void *arg, dmu_tx_t *tx)
 			return (SET_ERROR(EINVAL));
 
 		/* Open the parent of tofs */
-		ASSERT3U(strlen(tofs), <, MAXNAMELEN);
+		ASSERT3U(strlen(tofs), <, sizeof (buf));
 		(void) strlcpy(buf, tofs, strrchr(tofs, '/') - tofs + 1);
 		error = dsl_dataset_hold(dp, buf, FTAG, &ds);
 		if (error != 0)
@@ -1551,7 +1551,8 @@ dmu_recv_resume_begin_check(void *arg, dmu_tx_t *tx)
 	    !spa_feature_is_enabled(dp->dp_spa, SPA_FEATURE_LZ4_COMPRESS))
 		return (SET_ERROR(ENOTSUP));
 
-	char recvname[ZFS_MAXNAMELEN];
+	/* 6 extra bytes for /%recv */
+	char recvname[ZFS_MAX_DATASET_NAME_LEN + 6];
 
 	(void) snprintf(recvname, sizeof (recvname), "%s/%s",
 	    tofs, recv_clone_name);
@@ -1624,7 +1625,8 @@ dmu_recv_resume_begin_sync(void *arg, dmu_tx_t *tx)
 	const char *tofs = drba->drba_cookie->drc_tofs;
 	dsl_dataset_t *ds;
 	uint64_t dsobj;
-	char recvname[ZFS_MAXNAMELEN];
+	/* 6 extra bytes for /%recv */
+	char recvname[ZFS_MAX_DATASET_NAME_LEN + 6];
 
 	(void) snprintf(recvname, sizeof (recvname), "%s/%s",
 	    tofs, recv_clone_name);
@@ -2364,7 +2366,7 @@ dmu_recv_cleanup_ds(dmu_recv_cookie_t *drc)
 		txg_wait_synced(drc->drc_ds->ds_dir->dd_pool, 0);
 		dsl_dataset_disown(drc->drc_ds, dmu_recv_tag);
 	} else {
-		char name[MAXNAMELEN];
+		char name[ZFS_MAX_DATASET_NAME_LEN];
 		dsl_dataset_name(drc->drc_ds, name);
 		dsl_dataset_disown(drc->drc_ds, dmu_recv_tag);
 		(void) dsl_destroy_head(name);
@@ -3183,13 +3185,13 @@ static int
 dmu_recv_existing_end(dmu_recv_cookie_t *drc)
 {
 	int error;
-	char name[MAXNAMELEN];
 
 #ifdef _KERNEL
 	/*
 	 * We will be destroying the ds; make sure its origin is unmounted if
 	 * necessary.
 	 */
+	char name[ZFS_MAX_DATASET_NAME_LEN];
 	dsl_dataset_name(drc->drc_ds, name);
 	zfs_destroy_unmount_origin(name);
 #endif
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_bookmark.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_bookmark.c
index bc08d1c..39d572c 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_bookmark.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_bookmark.c
@@ -34,10 +34,10 @@ static int
 dsl_bookmark_hold_ds(dsl_pool_t *dp, const char *fullname,
     dsl_dataset_t **dsp, void *tag, char **shortnamep)
 {
-	char buf[MAXNAMELEN];
+	char buf[ZFS_MAX_DATASET_NAME_LEN];
 	char *hashp;
 
-	if (strlen(fullname) >= MAXNAMELEN)
+	if (strlen(fullname) >= ZFS_MAX_DATASET_NAME_LEN)
 		return (SET_ERROR(ENAMETOOLONG));
 	hashp = strchr(fullname, '#');
 	if (hashp == NULL)
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c
index 00b9c7e..8d97789 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dataset.c
@@ -676,22 +676,37 @@ dsl_dataset_name(dsl_dataset_t *ds, char *name)
 		dsl_dir_name(ds->ds_dir, name);
 		VERIFY0(dsl_dataset_get_snapname(ds));
 		if (ds->ds_snapname[0]) {
-			(void) strcat(name, "@");
+			VERIFY3U(strlcat(name, "@", ZFS_MAX_DATASET_NAME_LEN),
+			    <, ZFS_MAX_DATASET_NAME_LEN);
 			/*
 			 * We use a "recursive" mutex so that we
 			 * can call dprintf_ds() with ds_lock held.
 			 */
 			if (!MUTEX_HELD(&ds->ds_lock)) {
 				mutex_enter(&ds->ds_lock);
-				(void) strcat(name, ds->ds_snapname);
+				VERIFY3U(strlcat(name, ds->ds_snapname,
+				    ZFS_MAX_DATASET_NAME_LEN), <,
+				    ZFS_MAX_DATASET_NAME_LEN);
 				mutex_exit(&ds->ds_lock);
 			} else {
-				(void) strcat(name, ds->ds_snapname);
+				VERIFY3U(strlcat(name, ds->ds_snapname,
+				    ZFS_MAX_DATASET_NAME_LEN), <,
+				    ZFS_MAX_DATASET_NAME_LEN);
 			}
 		}
 	}
 }
 
+int
+dsl_dataset_namelen(dsl_dataset_t *ds)
+{
+	VERIFY0(dsl_dataset_get_snapname(ds));
+	mutex_enter(&ds->ds_lock);
+	int len = dsl_dir_namelen(ds->ds_dir) + 1 + strlen(ds->ds_snapname);
+	mutex_exit(&ds->ds_lock);
+	return (len);
+}
+
 void
 dsl_dataset_rele(dsl_dataset_t *ds, void *tag)
 {
@@ -1296,10 +1311,10 @@ dsl_dataset_snapshot_check(void *arg, dmu_tx_t *tx)
 		int error = 0;
 		dsl_dataset_t *ds;
 		char *name, *atp;
-		char dsname[MAXNAMELEN];
+		char dsname[ZFS_MAX_DATASET_NAME_LEN];
 
 		name = nvpair_name(pair);
-		if (strlen(name) >= MAXNAMELEN)
+		if (strlen(name) >= ZFS_MAX_DATASET_NAME_LEN)
 			error = SET_ERROR(ENAMETOOLONG);
 		if (error == 0) {
 			atp = strchr(name, '@');
@@ -1474,7 +1489,7 @@ dsl_dataset_snapshot_sync(void *arg, dmu_tx_t *tx)
 	    pair != NULL; pair = nvlist_next_nvpair(ddsa->ddsa_snaps, pair)) {
 		dsl_dataset_t *ds;
 		char *name, *atp;
-		char dsname[MAXNAMELEN];
+		char dsname[ZFS_MAX_DATASET_NAME_LEN];
 
 		name = nvpair_name(pair);
 		atp = strchr(name, '@');
@@ -1520,7 +1535,7 @@ dsl_dataset_snapshot(nvlist_t *snaps, nvlist_t *props, nvlist_t *errors)
 		suspended = fnvlist_alloc();
 		for (pair = nvlist_next_nvpair(snaps, NULL); pair != NULL;
 		    pair = nvlist_next_nvpair(snaps, pair)) {
-			char fsname[MAXNAMELEN];
+			char fsname[ZFS_MAX_DATASET_NAME_LEN];
 			char *snapname = nvpair_name(pair);
 			char *atp;
 			void *cookie;
@@ -1738,7 +1753,7 @@ get_clones_stat(dsl_dataset_t *ds, nvlist_t *nv)
 	    zap_cursor_retrieve(&zc, &za) == 0;
 	    zap_cursor_advance(&zc)) {
 		dsl_dataset_t *clone;
-		char buf[ZFS_MAXNAMELEN];
+		char buf[ZFS_MAX_DATASET_NAME_LEN];
 		VERIFY0(dsl_dataset_hold_obj(ds->ds_dir->dd_pool,
 		    za.za_first_integer, FTAG, &clone));
 		dsl_dir_name(clone->ds_dir, buf);
@@ -1846,7 +1861,7 @@ dsl_dataset_stats(dsl_dataset_t *ds, nvlist_t *nv)
 		get_clones_stat(ds, nv);
 	} else {
 		if (ds->ds_prev != NULL && ds->ds_prev != dp->dp_origin_snap) {
-			char buf[MAXNAMELEN];
+			char buf[ZFS_MAX_DATASET_NAME_LEN];
 			dsl_dataset_name(ds->ds_prev, buf);
 			dsl_prop_nvlist_add_string(nv, ZFS_PROP_PREV_SNAP, buf);
 		}
@@ -1907,12 +1922,15 @@ dsl_dataset_stats(dsl_dataset_t *ds, nvlist_t *nv)
 		 * stats set on our child named "%recv".  Check the child
 		 * for the prop.
 		 */
-		char recvname[ZFS_MAXNAMELEN];
+		/* 6 extra bytes for /%recv */
+		char recvname[ZFS_MAX_DATASET_NAME_LEN + 6];
 		dsl_dataset_t *recv_ds;
 		dsl_dataset_name(ds, recvname);
-		(void) strcat(recvname, "/");
-		(void) strcat(recvname, recv_clone_name);
-		if (dsl_dataset_hold(dp, recvname, FTAG, &recv_ds) == 0) {
+		if (strlcat(recvname, "/", sizeof (recvname)) <
+		    sizeof (recvname) &&
+		    strlcat(recvname, recv_clone_name, sizeof (recvname)) <
+		    sizeof (recvname) &&
+		    dsl_dataset_hold(dp, recvname, FTAG, &recv_ds) == 0) {
 			get_receive_resume_stats(recv_ds, nv);
 			dsl_dataset_rele(recv_ds, FTAG);
 		}
@@ -2039,7 +2057,7 @@ dsl_dataset_rename_snapshot_check_impl(dsl_pool_t *dp,
 
 	/* dataset name + 1 for the "@" + the new snapshot name must fit */
 	if (dsl_dir_namelen(hds->ds_dir) + 1 +
-	    strlen(ddrsa->ddrsa_newsnapname) >= MAXNAMELEN)
+	    strlen(ddrsa->ddrsa_newsnapname) >= ZFS_MAX_DATASET_NAME_LEN)
 		error = SET_ERROR(ENAMETOOLONG);
 
 	return (error);
@@ -2287,7 +2305,7 @@ dsl_dataset_rollback_sync(void *arg, dmu_tx_t *tx)
 	dsl_pool_t *dp = dmu_tx_pool(tx);
 	dsl_dataset_t *ds, *clone;
 	uint64_t cloneobj;
-	char namebuf[ZFS_MAXNAMELEN];
+	char namebuf[ZFS_MAX_DATASET_NAME_LEN];
 
 	VERIFY0(dsl_dataset_hold(dp, ddra->ddra_fsname, FTAG, &ds));
 
@@ -2863,7 +2881,7 @@ promote_rele(dsl_dataset_promote_arg_t *ddpa, void *tag)
  * Promote a clone.
  *
  * If it fails due to a conflicting snapshot name, "conflsnap" will be filled
- * in with the name.  (It must be at least MAXNAMELEN bytes long.)
+ * in with the name.  (It must be at least ZFS_MAX_DATASET_NAME_LEN bytes long.)
  */
 int
 dsl_dataset_promote(const char *name, char *conflsnap)
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_deleg.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_deleg.c
index 9e9c19d..7870b49 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_deleg.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_deleg.c
@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2007, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2011, 2014 by Delphix. All rights reserved.
+ * Copyright (c) 2011, 2015 by Delphix. All rights reserved.
  */
 
 /*
@@ -330,7 +330,7 @@ dsl_deleg_get(const char *ddname, nvlist_t **nvp)
 		zap_attribute_t baseza;
 		nvlist_t *sp_nvp;
 		uint64_t n;
-		char source[MAXNAMELEN];
+		char source[ZFS_MAX_DATASET_NAME_LEN];
 
 		if (dsl_dir_phys(dd)->dd_deleg_zapobj == 0 ||
 		    zap_count(mos,
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dir.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dir.c
index 00341ad..224575e 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dir.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_dir.c
@@ -303,13 +303,14 @@ dsl_dir_async_rele(dsl_dir_t *dd, void *tag)
 	dmu_buf_rele(dd->dd_dbuf, tag);
 }
 
-/* buf must be long enough (MAXNAMELEN + strlen(MOS_DIR_NAME) + 1 should do) */
+/* buf must be at least ZFS_MAX_DATASET_NAME_LEN bytes */
 void
 dsl_dir_name(dsl_dir_t *dd, char *buf)
 {
 	if (dd->dd_parent) {
 		dsl_dir_name(dd->dd_parent, buf);
-		(void) strcat(buf, "/");
+		VERIFY3U(strlcat(buf, "/", ZFS_MAX_DATASET_NAME_LEN), <,
+		    ZFS_MAX_DATASET_NAME_LEN);
 	} else {
 		buf[0] = '\0';
 	}
@@ -319,10 +320,12 @@ dsl_dir_name(dsl_dir_t *dd, char *buf)
 		 * dprintf_dd() with dd_lock held
 		 */
 		mutex_enter(&dd->dd_lock);
-		(void) strcat(buf, dd->dd_myname);
+		VERIFY3U(strlcat(buf, dd->dd_myname, ZFS_MAX_DATASET_NAME_LEN),
+		    <, ZFS_MAX_DATASET_NAME_LEN);
 		mutex_exit(&dd->dd_lock);
 	} else {
-		(void) strcat(buf, dd->dd_myname);
+		VERIFY3U(strlcat(buf, dd->dd_myname, ZFS_MAX_DATASET_NAME_LEN),
+		    <, ZFS_MAX_DATASET_NAME_LEN);
 	}
 }
 
@@ -371,12 +374,12 @@ getcomponent(const char *path, char *component, const char **nextp)
 		if (p != NULL &&
 		    (p[0] != '@' || strpbrk(path+1, "/@") || p[1] == '\0'))
 			return (SET_ERROR(EINVAL));
-		if (strlen(path) >= MAXNAMELEN)
+		if (strlen(path) >= ZFS_MAX_DATASET_NAME_LEN)
 			return (SET_ERROR(ENAMETOOLONG));
 		(void) strcpy(component, path);
 		p = NULL;
 	} else if (p[0] == '/') {
-		if (p - path >= MAXNAMELEN)
+		if (p - path >= ZFS_MAX_DATASET_NAME_LEN)
 			return (SET_ERROR(ENAMETOOLONG));
 		(void) strncpy(component, path, p - path);
 		component[p - path] = '\0';
@@ -388,7 +391,7 @@ getcomponent(const char *path, char *component, const char **nextp)
 		 */
 		if (strchr(path, '/'))
 			return (SET_ERROR(EINVAL));
-		if (p - path >= MAXNAMELEN)
+		if (p - path >= ZFS_MAX_DATASET_NAME_LEN)
 			return (SET_ERROR(ENAMETOOLONG));
 		(void) strncpy(component, path, p - path);
 		component[p - path] = '\0';
@@ -410,7 +413,7 @@ int
 dsl_dir_hold(dsl_pool_t *dp, const char *name, void *tag,
     dsl_dir_t **ddp, const char **tailp)
 {
-	char buf[MAXNAMELEN];
+	char buf[ZFS_MAX_DATASET_NAME_LEN];
 	const char *spaname, *next, *nextnext = NULL;
 	int err;
 	dsl_dir_t *dd;
@@ -977,7 +980,7 @@ dsl_dir_stats(dsl_dir_t *dd, nvlist_t *nv)
 
 	if (dsl_dir_is_clone(dd)) {
 		dsl_dataset_t *ds;
-		char buf[MAXNAMELEN];
+		char buf[ZFS_MAX_DATASET_NAME_LEN];
 
 		VERIFY0(dsl_dataset_hold_obj(dd->dd_pool,
 		    dsl_dir_phys(dd)->dd_origin_obj, FTAG, &ds));
@@ -1685,11 +1688,11 @@ static int
 dsl_valid_rename(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
 {
 	int *deltap = arg;
-	char namebuf[MAXNAMELEN];
+	char namebuf[ZFS_MAX_DATASET_NAME_LEN];
 
 	dsl_dataset_name(ds, namebuf);
 
-	if (strlen(namebuf) + *deltap >= MAXNAMELEN)
+	if (strlen(namebuf) + *deltap >= ZFS_MAX_DATASET_NAME_LEN)
 		return (SET_ERROR(ENAMETOOLONG));
 	return (0);
 }
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_prop.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_prop.c
index 25a7d96..f57a511 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_prop.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_prop.c
@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
  * Copyright 2015, Joyent, Inc.
  */
 
@@ -1059,7 +1059,7 @@ dsl_prop_get_all_ds(dsl_dataset_t *ds, nvlist_t **nvp,
 	dsl_pool_t *dp = dd->dd_pool;
 	objset_t *mos = dp->dp_meta_objset;
 	int err = 0;
-	char setpoint[MAXNAMELEN];
+	char setpoint[ZFS_MAX_DATASET_NAME_LEN];
 
 	VERIFY(nvlist_alloc(nvp, NV_UNIQUE_NAME, KM_SLEEP) == 0);
 
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c
index f6408c8..89c8eba 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c
@@ -1115,7 +1115,7 @@ dsl_scan_visitds(dsl_scan_t *scn, uint64_t dsobj, dmu_tx_t *tx)
 	dmu_buf_will_dirty(ds->ds_dbuf, tx);
 	dsl_scan_visit_rootbp(scn, ds, &dsl_dataset_phys(ds)->ds_bp, tx);
 
-	char *dsname = kmem_alloc(ZFS_MAXNAMELEN, KM_SLEEP);
+	char *dsname = kmem_alloc(ZFS_MAX_DATASET_NAME_LEN, KM_SLEEP);
 	dsl_dataset_name(ds, dsname);
 	zfs_dbgmsg("scanned dataset %llu (%s) with min=%llu max=%llu; "
 	    "pausing=%u",
@@ -1123,7 +1123,7 @@ dsl_scan_visitds(dsl_scan_t *scn, uint64_t dsobj, dmu_tx_t *tx)
 	    (longlong_t)scn->scn_phys.scn_cur_min_txg,
 	    (longlong_t)scn->scn_phys.scn_cur_max_txg,
 	    (int)scn->scn_pausing);
-	kmem_free(dsname, ZFS_MAXNAMELEN);
+	kmem_free(dsname, ZFS_MAX_DATASET_NAME_LEN);
 
 	if (scn->scn_pausing)
 		goto out;
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_userhold.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_userhold.c
index a67db5f..54a15e1 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_userhold.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_userhold.c
@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
  * Copyright (c) 2013 Steven Hartland. All rights reserved.
  */
 
@@ -180,7 +180,7 @@ dsl_dataset_user_hold_sync_one_impl(nvlist_t *tmpholds, dsl_dataset_t *ds,
 }
 
 typedef struct zfs_hold_cleanup_arg {
-	char zhca_spaname[MAXNAMELEN];
+	char zhca_spaname[ZFS_MAX_DATASET_NAME_LEN];
 	uint64_t zhca_spa_load_guid;
 	nvlist_t *zhca_holds;
 } zfs_hold_cleanup_arg_t;
@@ -574,7 +574,7 @@ dsl_dataset_user_release_impl(nvlist_t *holds, nvlist_t *errlist,
 			error = dsl_dataset_hold_obj_string(tmpdp,
 			    nvpair_name(pair), FTAG, &ds);
 			if (error == 0) {
-				char name[MAXNAMELEN];
+				char name[ZFS_MAX_DATASET_NAME_LEN];
 				dsl_dataset_name(ds, name);
 				dsl_pool_config_exit(tmpdp, FTAG);
 				dsl_dataset_rele(ds, FTAG);
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa.c
index 581b845..cc24390 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa.c
@@ -370,8 +370,7 @@ spa_prop_get(spa_t *spa, nvlist_t **nvp)
 					break;
 				}
 
-				strval = kmem_alloc(
-				    MAXNAMELEN + strlen(MOS_DIR_NAME) + 1,
+				strval = kmem_alloc(ZFS_MAX_DATASET_NAME_LEN,
 				    KM_SLEEP);
 				dsl_dataset_name(ds, strval);
 				dsl_dataset_rele(ds, FTAG);
@@ -384,8 +383,7 @@ spa_prop_get(spa_t *spa, nvlist_t **nvp)
 			spa_prop_add_list(*nvp, prop, strval, intval, src);
 
 			if (strval != NULL)
-				kmem_free(strval,
-				    MAXNAMELEN + strlen(MOS_DIR_NAME) + 1);
+				kmem_free(strval, ZFS_MAX_DATASET_NAME_LEN);
 
 			break;
 
@@ -2000,11 +1998,8 @@ spa_load_verify_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
 int
 verify_dataset_name_len(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
 {
-	char namebuf[MAXPATHLEN];
-	dsl_dataset_name(ds, namebuf);
-	if (strlen(namebuf) > MAXNAMELEN) {
+	if (dsl_dataset_namelen(ds) >= ZFS_MAX_DATASET_NAME_LEN)
 		return (SET_ERROR(ENAMETOOLONG));
-	}
 
 	return (0);
 }
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa_history.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa_history.c
index 8965686..02147b4 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa_history.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa_history.c
@@ -21,7 +21,7 @@
 
 /*
  * Copyright (c) 2006, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2011, 2014 by Delphix. All rights reserved.
+ * Copyright (c) 2011, 2015 by Delphix. All rights reserved.
  * Copyright (c) 2014 Integros [integros.com]
  */
 
@@ -501,7 +501,7 @@ spa_history_log_internal_ds(dsl_dataset_t *ds, const char *operation,
     dmu_tx_t *tx, const char *fmt, ...)
 {
 	va_list adx;
-	char namebuf[MAXNAMELEN];
+	char namebuf[ZFS_MAX_DATASET_NAME_LEN];
 	nvlist_t *nvl = fnvlist_alloc();
 
 	ASSERT(tx != NULL);
@@ -520,7 +520,7 @@ spa_history_log_internal_dd(dsl_dir_t *dd, const char *operation,
     dmu_tx_t *tx, const char *fmt, ...)
 {
 	va_list adx;
-	char namebuf[MAXNAMELEN];
+	char namebuf[ZFS_MAX_DATASET_NAME_LEN];
 	nvlist_t *nvl = fnvlist_alloc();
 
 	ASSERT(tx != NULL);
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h
index 8a8f29c..6452828 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h
@@ -816,7 +816,7 @@ typedef struct dmu_objset_stats {
 	dmu_objset_type_t dds_type;
 	uint8_t dds_is_snapshot;
 	uint8_t dds_inconsistent;
-	char dds_origin[MAXNAMELEN];
+	char dds_origin[ZFS_MAX_DATASET_NAME_LEN];
 } dmu_objset_stats_t;
 
 /*
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_dataset.h b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_dataset.h
index 766ae3c..17d15d7 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_dataset.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_dataset.h
@@ -221,7 +221,7 @@ typedef struct dsl_dataset {
 	uint8_t ds_feature_activation_needed[SPA_FEATURES];
 
 	/* Protected by ds_lock; keep at end of struct for better locality */
-	char ds_snapname[MAXNAMELEN];
+	char ds_snapname[ZFS_MAX_DATASET_NAME_LEN];
 } dsl_dataset_t;
 
 inline dsl_dataset_phys_t *
@@ -256,6 +256,7 @@ int dsl_dataset_own_obj(struct dsl_pool *dp, uint64_t dsobj,
 void dsl_dataset_disown(dsl_dataset_t *ds, void *tag);
 void dsl_dataset_name(dsl_dataset_t *ds, char *name);
 boolean_t dsl_dataset_tryown(dsl_dataset_t *ds, void *tag);
+int dsl_dataset_namelen(dsl_dataset_t *ds);
 boolean_t dsl_dataset_has_owner(dsl_dataset_t *ds);
 uint64_t dsl_dataset_create_sync(dsl_dir_t *pds, const char *lastname,
     dsl_dataset_t *origin, uint64_t flags, cred_t *, dmu_tx_t *);
@@ -347,10 +348,10 @@ void dsl_dataset_deactivate_feature(uint64_t dsobj,
 #ifdef ZFS_DEBUG
 #define	dprintf_ds(ds, fmt, ...) do { \
 	if (zfs_flags & ZFS_DEBUG_DPRINTF) { \
-	char *__ds_name = kmem_alloc(MAXNAMELEN, KM_SLEEP); \
+	char *__ds_name = kmem_alloc(ZFS_MAX_DATASET_NAME_LEN, KM_SLEEP); \
 	dsl_dataset_name(ds, __ds_name); \
 	dprintf("ds=%s " fmt, __ds_name, __VA_ARGS__); \
-	kmem_free(__ds_name, MAXNAMELEN); \
+	kmem_free(__ds_name, ZFS_MAX_DATASET_NAME_LEN); \
 	} \
 _NOTE(CONSTCOND) } while (0)
 #else
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_dir.h b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_dir.h
index 93fb73f..ab2d740 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_dir.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_dir.h
@@ -112,7 +112,7 @@ struct dsl_dir {
 	int64_t dd_space_towrite[TXG_SIZE];
 
 	/* protected by dd_lock; keep at end of struct for better locality */
-	char dd_myname[MAXNAMELEN];
+	char dd_myname[ZFS_MAX_DATASET_NAME_LEN];
 };
 
 inline dsl_dir_phys_t *
@@ -176,11 +176,10 @@ boolean_t dsl_dir_is_zapified(dsl_dir_t *dd);
 #ifdef ZFS_DEBUG
 #define	dprintf_dd(dd, fmt, ...) do { \
 	if (zfs_flags & ZFS_DEBUG_DPRINTF) { \
-	char *__ds_name = kmem_alloc(MAXNAMELEN + strlen(MOS_DIR_NAME) + 1, \
-	    KM_SLEEP); \
+	char *__ds_name = kmem_alloc(ZFS_MAX_DATASET_NAME_LEN, KM_SLEEP); \
 	dsl_dir_name(dd, __ds_name); \
 	dprintf("dd=%s " fmt, __ds_name, __VA_ARGS__); \
-	kmem_free(__ds_name, MAXNAMELEN + strlen(MOS_DIR_NAME) + 1); \
+	kmem_free(__ds_name, ZFS_MAX_DATASET_NAME_LEN); \
 	} \
 _NOTE(CONSTCOND) } while (0)
 #else
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/spa_impl.h b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/spa_impl.h
index 0a25b6c..0e24c56 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/spa_impl.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/spa_impl.h
@@ -127,7 +127,7 @@ struct spa {
 	/*
 	 * Fields protected by spa_namespace_lock.
 	 */
-	char		spa_name[MAXNAMELEN];	/* pool name */
+	char		spa_name[ZFS_MAX_DATASET_NAME_LEN];	/* pool name */
 	char		*spa_comment;		/* comment */
 	avl_node_t	spa_avl;		/* node in spa_namespace_avl */
 	nvlist_t	*spa_config;		/* last synced config */
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zap.h b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zap.h
index 9c3783f..2f5ce88 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zap.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zap.h
@@ -344,7 +344,7 @@ typedef struct {
 	boolean_t za_normalization_conflict;
 	uint64_t za_num_integers;
 	uint64_t za_first_integer;	/* no sign extension for <8byte ints */
-	char za_name[MAXNAMELEN];
+	char za_name[ZAP_MAXNAMELEN];
 } zap_attribute_t;
 
 /*
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_znode.h b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_znode.h
index 7649295..79728c1 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_znode.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zfs_znode.h
@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
  * Copyright (c) 2014 Integros [integros.com]
  */
 
@@ -135,17 +135,6 @@ extern "C" {
 #define	ZFS_SA_ATTRS		"SA_ATTRS"
 
 /*
- * Path component length
- *
- * The generic fs code uses MAXNAMELEN to represent
- * what the largest component length is.  Unfortunately,
- * this length includes the terminating NULL.  ZFS needs
- * to tell the users via pathconf() and statvfs() what the
- * true maximum length of a component is, excluding the NULL.
- */
-#define	ZFS_MAXNAMELEN	(MAXNAMELEN - 1)
-
-/*
  * Convert mode bits (zp_mode) to BSD-style DT_* values for storing in
  * the directory entries.
  */
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ctldir.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ctldir.c
index cbafa03..9eaa7d2 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ctldir.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ctldir.c
@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2013 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
  * Copyright 2015, OmniTI Computer Consulting, Inc. All rights reserved.
  */
 
@@ -787,8 +787,8 @@ zfsctl_snapdir_rename(vnode_t *sdvp, char *snm, vnode_t *tdvp, char *tnm,
 	zfs_snapentry_t search, *sep;
 	zfsvfs_t *zfsvfs;
 	avl_index_t where;
-	char from[MAXNAMELEN], to[MAXNAMELEN];
-	char real[MAXNAMELEN], fsname[MAXNAMELEN];
+	char from[ZFS_MAX_DATASET_NAME_LEN], to[ZFS_MAX_DATASET_NAME_LEN];
+	char real[ZFS_MAX_DATASET_NAME_LEN], fsname[ZFS_MAX_DATASET_NAME_LEN];
 	int err;
 
 	zfsvfs = sdvp->v_vfsp->vfs_data;
@@ -796,7 +796,7 @@ zfsctl_snapdir_rename(vnode_t *sdvp, char *snm, vnode_t *tdvp, char *tnm,
 
 	if ((flags & FIGNORECASE) || zfsvfs->z_case == ZFS_CASE_INSENSITIVE) {
 		err = dmu_snapshot_realname(zfsvfs->z_os, snm, real,
-		    MAXNAMELEN, NULL);
+		    sizeof (real), NULL);
 		if (err == 0) {
 			snm = real;
 		} else if (err != ENOTSUP) {
@@ -809,9 +809,9 @@ zfsctl_snapdir_rename(vnode_t *sdvp, char *snm, vnode_t *tdvp, char *tnm,
 
 	dmu_objset_name(zfsvfs->z_os, fsname);
 
-	err = zfsctl_snapshot_zname(sdvp, snm, MAXNAMELEN, from);
+	err = zfsctl_snapshot_zname(sdvp, snm, sizeof (from), from);
 	if (err == 0)
-		err = zfsctl_snapshot_zname(tdvp, tnm, MAXNAMELEN, to);
+		err = zfsctl_snapshot_zname(tdvp, tnm, sizeof (to), to);
 	if (err == 0)
 		err = zfs_secpolicy_rename_perms(from, to, cr);
 	if (err != 0)
@@ -854,8 +854,8 @@ zfsctl_snapdir_remove(vnode_t *dvp, char *name, vnode_t *cwd, cred_t *cr,
 	zfs_snapentry_t *sep;
 	zfs_snapentry_t search;
 	zfsvfs_t *zfsvfs;
-	char snapname[MAXNAMELEN];
-	char real[MAXNAMELEN];
+	char snapname[ZFS_MAX_DATASET_NAME_LEN];
+	char real[ZFS_MAX_DATASET_NAME_LEN];
 	int err;
 
 	zfsvfs = dvp->v_vfsp->vfs_data;
@@ -864,7 +864,7 @@ zfsctl_snapdir_remove(vnode_t *dvp, char *name, vnode_t *cwd, cred_t *cr,
 	if ((flags & FIGNORECASE) || zfsvfs->z_case == ZFS_CASE_INSENSITIVE) {
 
 		err = dmu_snapshot_realname(zfsvfs->z_os, name, real,
-		    MAXNAMELEN, NULL);
+		    sizeof (real), NULL);
 		if (err == 0) {
 			name = real;
 		} else if (err != ENOTSUP) {
@@ -875,7 +875,7 @@ zfsctl_snapdir_remove(vnode_t *dvp, char *name, vnode_t *cwd, cred_t *cr,
 
 	ZFS_EXIT(zfsvfs);
 
-	err = zfsctl_snapshot_zname(dvp, name, MAXNAMELEN, snapname);
+	err = zfsctl_snapshot_zname(dvp, name, sizeof (snapname), snapname);
 	if (err == 0)
 		err = zfs_secpolicy_destroy_perms(snapname, cr);
 	if (err != 0)
@@ -911,7 +911,7 @@ zfsctl_snapdir_mkdir(vnode_t *dvp, char *dirname, vattr_t *vap, vnode_t  **vpp,
     cred_t *cr, caller_context_t *cc, int flags, vsecattr_t *vsecp)
 {
 	zfsvfs_t *zfsvfs = dvp->v_vfsp->vfs_data;
-	char name[MAXNAMELEN];
+	char name[ZFS_MAX_DATASET_NAME_LEN];
 	int err;
 	static enum symfollow follow = NO_FOLLOW;
 	static enum uio_seg seg = UIO_SYSSPACE;
@@ -973,8 +973,8 @@ zfsctl_snapdir_lookup(ap)
 	char nm[NAME_MAX + 1];
 	zfsctl_snapdir_t *sdp = dvp->v_data;
 	objset_t *snap;
-	char snapname[MAXNAMELEN];
-	char real[MAXNAMELEN];
+	char snapname[ZFS_MAX_DATASET_NAME_LEN];
+	char real[ZFS_MAX_DATASET_NAME_LEN];
 	char *mountpoint;
 	zfs_snapentry_t *sep, search;
 	size_t mountpoint_len;
@@ -1019,7 +1019,7 @@ zfsctl_snapdir_lookup(ap)
 		boolean_t conflict = B_FALSE;
 
 		err = dmu_snapshot_realname(zfsvfs->z_os, nm, real,
-		    MAXNAMELEN, &conflict);
+		    sizeof (real), &conflict);
 		if (err == 0) {
 			strlcpy(nm, real, sizeof(nm));
 		} else if (err != ENOTSUP) {
@@ -1060,7 +1060,7 @@ relookup:
 	/*
 	 * The requested snapshot is not currently mounted, look it up.
 	 */
-	err = zfsctl_snapshot_zname(dvp, nm, MAXNAMELEN, snapname);
+	err = zfsctl_snapshot_zname(dvp, nm, sizeof (snapname), snapname);
 	if (err != 0) {
 		mutex_exit(&sdp->sd_lock);
 		ZFS_EXIT(zfsvfs);
@@ -1197,7 +1197,7 @@ zfsctl_snapdir_readdir_cb(vnode_t *vp, void *dp, int *eofp,
     offset_t *offp, offset_t *nextp, void *data, int flags)
 {
 	zfsvfs_t *zfsvfs = vp->v_vfsp->vfs_data;
-	char snapname[MAXNAMELEN];
+	char snapname[ZFS_MAX_DATASET_NAME_LEN];
 	uint64_t id, cookie;
 	boolean_t case_conflict;
 	int error;
@@ -1206,8 +1206,8 @@ zfsctl_snapdir_readdir_cb(vnode_t *vp, void *dp, int *eofp,
 
 	cookie = *offp;
 	dsl_pool_config_enter(dmu_objset_pool(zfsvfs->z_os), FTAG);
-	error = dmu_snapshot_list_next(zfsvfs->z_os, MAXNAMELEN, snapname, &id,
-	    &cookie, &case_conflict);
+	error = dmu_snapshot_list_next(zfsvfs->z_os,
+	    sizeof (snapname), snapname, &id, &cookie, &case_conflict);
 	dsl_pool_config_exit(dmu_objset_pool(zfsvfs->z_os), FTAG);
 	if (error) {
 		ZFS_EXIT(zfsvfs);
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ioctl.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ioctl.c
index ae2a4ad..ec6c698 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ioctl.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ioctl.c
@@ -639,7 +639,7 @@ zfs_secpolicy_setprop(const char *dsname, zfs_prop_t prop, nvpair_t *propval,
 	case ZFS_PROP_SNAPSHOT_LIMIT:
 		if (!INGLOBALZONE(curthread)) {
 			uint64_t zoned;
-			char setpoint[MAXNAMELEN];
+			char setpoint[ZFS_MAX_DATASET_NAME_LEN];
 			/*
 			 * Unprivileged users are allowed to modify the
 			 * limit on things *under* (ie. contained by)
@@ -875,7 +875,7 @@ zfs_secpolicy_destroy_snaps(zfs_cmd_t *zc, nvlist_t *innvl, cred_t *cr)
 int
 zfs_secpolicy_rename_perms(const char *from, const char *to, cred_t *cr)
 {
-	char	parentname[MAXNAMELEN];
+	char	parentname[ZFS_MAX_DATASET_NAME_LEN];
 	int	error;
 
 	if ((error = zfs_secpolicy_write_perms(from,
@@ -947,7 +947,7 @@ zfs_secpolicy_promote(zfs_cmd_t *zc, nvlist_t *innvl, cred_t *cr)
 	error = dsl_dataset_hold(dp, zc->zc_name, FTAG, &clone);
 
 	if (error == 0) {
-		char parentname[MAXNAMELEN];
+		char parentname[ZFS_MAX_DATASET_NAME_LEN];
 		dsl_dataset_t *origin = NULL;
 		dsl_dir_t *dd;
 		dd = clone->ds_dir;
@@ -1116,7 +1116,7 @@ zfs_secpolicy_log_history(zfs_cmd_t *zc, nvlist_t *innvl, cred_t *cr)
 static int
 zfs_secpolicy_create_clone(zfs_cmd_t *zc, nvlist_t *innvl, cred_t *cr)
 {
-	char	parentname[MAXNAMELEN];
+	char	parentname[ZFS_MAX_DATASET_NAME_LEN];
 	int	error;
 	char	*origin;
 
@@ -1259,7 +1259,7 @@ zfs_secpolicy_hold(zfs_cmd_t *zc, nvlist_t *innvl, cred_t *cr)
 
 	for (pair = nvlist_next_nvpair(holds, NULL); pair != NULL;
 	    pair = nvlist_next_nvpair(holds, pair)) {
-		char fsname[MAXNAMELEN];
+		char fsname[ZFS_MAX_DATASET_NAME_LEN];
 		error = dmu_fsname(nvpair_name(pair), fsname);
 		if (error != 0)
 			return (error);
@@ -1280,7 +1280,7 @@ zfs_secpolicy_release(zfs_cmd_t *zc, nvlist_t *innvl, cred_t *cr)
 
 	for (pair = nvlist_next_nvpair(innvl, NULL); pair != NULL;
 	    pair = nvlist_next_nvpair(innvl, pair)) {
-		char fsname[MAXNAMELEN];
+		char fsname[ZFS_MAX_DATASET_NAME_LEN];
 		error = dmu_fsname(nvpair_name(pair), fsname);
 		if (error != 0)
 			return (error);
@@ -2352,7 +2352,8 @@ zfs_ioc_snapshot_list_next(zfs_cmd_t *zc)
 	 * A dataset name of maximum length cannot have any snapshots,
 	 * so exit immediately.
 	 */
-	if (strlcat(zc->zc_name, "@", sizeof (zc->zc_name)) >= MAXNAMELEN) {
+	if (strlcat(zc->zc_name, "@", sizeof (zc->zc_name)) >=
+	    ZFS_MAX_DATASET_NAME_LEN) {
 		dmu_objset_rele(os, FTAG);
 		return (SET_ERROR(ESRCH));
 	}
@@ -3156,7 +3157,7 @@ zfs_fill_zplprops(const char *dataset, nvlist_t *createprops,
 	boolean_t fuids_ok, sa_ok;
 	uint64_t zplver = ZPL_VERSION;
 	objset_t *os = NULL;
-	char parentname[MAXNAMELEN];
+	char parentname[ZFS_MAX_DATASET_NAME_LEN];
 	char *cp;
 	spa_t *spa;
 	uint64_t spa_vers;
@@ -3535,7 +3536,7 @@ zfs_destroy_unmount_origin(const char *fsname)
 		return;
 	ds = dmu_objset_ds(os);
 	if (dsl_dir_is_clone(ds->ds_dir) && DS_IS_DEFER_DESTROY(ds->ds_prev)) {
-		char originname[MAXNAMELEN];
+		char originname[ZFS_MAX_DATASET_NAME_LEN];
 		dsl_dataset_name(ds->ds_prev, originname);
 		dmu_objset_rele(os, FTAG);
 		(void) zfs_unmount_snap(originname);
@@ -3755,7 +3756,7 @@ static int
 recursive_unmount(const char *fsname, void *arg)
 {
 	const char *snapname = arg;
-	char fullname[MAXNAMELEN];
+	char fullname[ZFS_MAX_DATASET_NAME_LEN];
 
 	(void) snprintf(fullname, sizeof (fullname), "%s@%s", fsname, snapname);
 	return (zfs_unmount_snap(fullname));
@@ -4290,7 +4291,7 @@ zfs_ioc_recv(zfs_cmd_t *zc)
 	nvlist_t *delayprops = NULL; /* sent properties applied post-receive */
 	char *origin = NULL;
 	char *tosnap;
-	char tofs[ZFS_MAXNAMELEN];
+	char tofs[ZFS_MAX_DATASET_NAME_LEN];
 	cap_rights_t rights;
 	boolean_t first_recvd_props = B_FALSE;
 
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vfsops.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vfsops.c
index a9da14c..fbaa324 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vfsops.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vfsops.c
@@ -1790,7 +1790,7 @@ zfs_statfs(vfs_t *vfsp, struct statfs *statp)
 	strlcpy(statp->f_mntonname, vfsp->mnt_stat.f_mntonname,
 	    sizeof(statp->f_mntonname));
 
-	statp->f_namemax = ZFS_MAXNAMELEN;
+	statp->f_namemax = MAXNAMELEN - 1;
 
 	ZFS_EXIT(zfsvfs);
 	return (0);
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zil.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zil.c
index 993a468..31ff734 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zil.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zil.c
@@ -1970,7 +1970,7 @@ typedef struct zil_replay_arg {
 static int
 zil_replay_error(zilog_t *zilog, lr_t *lr, int error)
 {
-	char name[MAXNAMELEN];
+	char name[ZFS_MAX_DATASET_NAME_LEN];
 
 	zilog->zl_replaying_seq--;	/* didn't actually replay this one */
 
diff --git a/sys/cddl/contrib/opensolaris/uts/common/sys/fs/zfs.h b/sys/cddl/contrib/opensolaris/uts/common/sys/fs/zfs.h
index ef24fc3..7e129e6 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/sys/fs/zfs.h
+++ b/sys/cddl/contrib/opensolaris/uts/common/sys/fs/zfs.h
@@ -74,9 +74,13 @@ typedef enum dmu_objset_type {
 #define	ZFS_TYPE_DATASET	\
 	(ZFS_TYPE_FILESYSTEM | ZFS_TYPE_VOLUME | ZFS_TYPE_SNAPSHOT)
 
+/*
+ * All of these include the terminating NUL byte.
+ */
 #define	ZAP_MAXNAMELEN 256
 #define	ZAP_MAXVALUELEN (1024 * 8)
 #define	ZAP_OLDMAXVALUELEN 1024
+#define	ZFS_MAX_DATASET_NAME_LEN 256
 
 /*
  * Dataset properties are identified by these constants and must be added to