Fix 2 bugs in non-raw send with encryption

Bisecting identified the redacted send/receive as the source of the bug
for issue #12014. Specifically the call to
dsl_dataset_hold_obj(&fromds) has been replaced by
dsl_dataset_hold_obj_flags() which passes a DECRYPT flag and creates
a key mapping. A subsequent dsl_dataset_rele_flag(&fromds) is missing
and the key mapping is not cleared. This may be inadvertedly used, which
results in arc_untransform failing with ECKSUM in:
 arc_untransform+0x96/0xb0 [zfs]
 dbuf_read_verify_dnode_crypt+0x196/0x350 [zfs]
 dbuf_read+0x56/0x770 [zfs]
 dmu_buf_hold_by_dnode+0x4a/0x80 [zfs]
 zap_lockdir+0x87/0xf0 [zfs]
 zap_lookup_norm+0x5c/0xd0 [zfs]
 zap_lookup+0x16/0x20 [zfs]
 zfs_get_zplprop+0x8d/0x1d0 [zfs]
 setup_featureflags+0x267/0x2e0 [zfs]
 dmu_send_impl+0xe7/0xcb0 [zfs]
 dmu_send_obj+0x265/0x360 [zfs]
 zfs_ioc_send+0x10c/0x280 [zfs]

Fix this by restoring the call to dsl_dataset_hold_obj().

The same applies for to_ds: here replace dsl_dataset_rele(&to_ds) with
dsl_dataset_rele_flags().

Both leaked key mappings will cause a panic when exporting the
sending pool or unloading the zfs module after a non-raw send from
an encrypted filesystem.

Contributions-by: Hank Barta <[email protected]>
Contributions-by: Paul Dagnelie <[email protected]>
Reviewed-by: Alexander Motin <[email protected]>
Reviewed-by: Richard Yao <[email protected]>
Reviewed-by: Rob Norris <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: George Amanakis <[email protected]>
Closes #12014 
Closes #17340

Author: gamanakis

module/zfs/dmu_send.c

@@ -2687,8 +2687,8 @@ dmu_send_obj(const char *pool, uint64_t tosnap, uint64_t fromsnap,
 	}
 
 	if (fromsnap != 0) {
-		err = dsl_dataset_hold_obj_flags(dspp.dp, fromsnap, dsflags,
-		    FTAG, &fromds);
+		err = dsl_dataset_hold_obj(dspp.dp, fromsnap, FTAG, &fromds);
+
 		if (err != 0) {
 			dsl_dataset_rele_flags(dspp.to_ds, dsflags, FTAG);
 			dsl_pool_rele(dspp.dp, FTAG);
@@ -2740,7 +2740,7 @@ dmu_send_obj(const char *pool, uint64_t tosnap, uint64_t fromsnap,
 		kmem_free(dspp.fromredactsnaps,
 		    dspp.numfromredactsnaps * sizeof (uint64_t));
 
-	dsl_dataset_rele(dspp.to_ds, FTAG);
+	dsl_dataset_rele_flags(dspp.to_ds, dsflags, FTAG);
 	return (err);
 }