Handle compressed buffers in __dbuf_hold_impl()

In __dbuf_hold_impl(), if a buffer is currently syncing and is still
referenced from db_data, a copy is made in case it is dirtied again in
the txg.  Previously, the buffer for the copy was simply allocated with
arc_alloc_buf() which doesn't handle compressed or encrypted buffers
(which are a special case of a compressed buffer).  The result was
typically an invalid memory access because the newly-allocated buffer
was of the uncompressed size.

This commit fixes the problem by handling the 2 compressed cases,
encrypted and unencrypted, respectively, with arc_alloc_raw_buf() and
arc_alloc_compressed_buf().

Although using the proper allocation functions fixes the invalid memory
access by allocating a buffer of the compressed size, another unrelated
issue made it impossible to properly detect compressed buffers in the
first place.  The header's compression flag was set to ZIO_COMPRESS_OFF
in arc_write() when it was possible that an attached buffer was actually
compressed.  This commit adds logic to only set ZIO_COMPRESS_OFF in
the non-ZIO_RAW case which wil handle both cases of compressed buffers
(encrypted or unencrypted).

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Tim Chase <[email protected]>
Closes openzfs#5742 
Closes openzfs#6797

module/zfs/arc.c

@@ -6936,7 +6936,8 @@ arc_write(zio_t *pio, spa_t *spa, uint64_t txg,
 	if (HDR_HAS_RABD(hdr))
 		arc_hdr_free_abd(hdr, B_TRUE);
 
-	arc_hdr_set_compress(hdr, ZIO_COMPRESS_OFF);
+	if (!(zio_flags & ZIO_FLAG_RAW))
+		arc_hdr_set_compress(hdr, ZIO_COMPRESS_OFF);
 
 	ASSERT(!arc_buf_is_shared(buf));
 	ASSERT3P(hdr->b_l1hdr.b_pabd, ==, NULL);

module/zfs/dbuf.c

@@ -2700,8 +2700,8 @@ dbuf_prefetch(dnode_t *dn, int64_t level, uint64_t blkid, zio_priority_t prio,
 
 /*
  * Helper function for __dbuf_hold_impl() to copy a buffer. Handles
- * the case of compressed and uncompressed buffers by allocating the
- * new buffer, respectively, with arc_alloc_raw_buf(),
+ * the case of encrypted, compressed and uncompressed buffers by
+ * allocating the new buffer, respectively, with arc_alloc_raw_buf(),
  * arc_alloc_compressed_buf() or arc_alloc_buf().*
  *
  * NOTE: Declared noinline to avoid stack bloat in __dbuf_hold_impl().
@@ -2716,7 +2716,18 @@ dbuf_hold_copy(struct dbuf_hold_impl_data *dh)
 
 	enum zio_compress compress_type = arc_get_compression(data);
 
-	if (compress_type != ZIO_COMPRESS_OFF) {
+	if (arc_is_encrypted(data)) {
+		boolean_t byteorder;
+		uint8_t salt[ZIO_DATA_SALT_LEN];
+		uint8_t iv[ZIO_DATA_IV_LEN];
+		uint8_t mac[ZIO_DATA_MAC_LEN];
+
+		arc_get_raw_params(data, &byteorder, salt, iv, mac);
+		dbuf_set_data(db, arc_alloc_raw_buf(dn->dn_objset->os_spa, db,
+		    dmu_objset_id(dn->dn_objset), byteorder, salt, iv, mac,
+		    dn->dn_type, arc_buf_size(data), arc_buf_lsize(data),
+		    compress_type));
+	} else if (compress_type != ZIO_COMPRESS_OFF) {
 		dbuf_set_data(db, arc_alloc_compressed_buf(
 		    dn->dn_objset->os_spa, db, arc_buf_size(data),
 		    arc_buf_lsize(data), compress_type));