reftable: fix resource leak in block.c error path

Add test coverage for corrupt zlib data. Fix memory leaks demonstrated by
unittest.

This problem was discovered by a Coverity scan.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

reftable/block.c

@@ -188,13 +188,16 @@ int block_reader_init(struct block_reader *br, struct reftable_block *block,
 	uint32_t full_block_size = table_block_size;
 	uint8_t typ = block->data[header_off];
 	uint32_t sz = get_be24(block->data + header_off + 1);
-
+	int err = 0;
 	uint16_t restart_count = 0;
 	uint32_t restart_start = 0;
 	uint8_t *restart_bytes = NULL;
+	uint8_t *uncompressed = NULL;
 
-	if (!reftable_is_block_type(typ))
+	if (!reftable_is_block_type(typ)) {
-		return REFTABLE_FORMAT_ERROR;
+		err =  REFTABLE_FORMAT_ERROR;
+		goto done;
+	}
 
 	if (typ == BLOCK_TYPE_LOG) {
 		int block_header_skip = 4 + header_off;
@@ -203,7 +206,7 @@ int block_reader_init(struct block_reader *br, struct reftable_block *block,
 		uLongf src_len = block->len - block_header_skip;
 		/* Log blocks specify the *uncompressed* size in their header.
 		 */
-		uint8_t *uncompressed = reftable_malloc(sz);
+		uncompressed = reftable_malloc(sz);
 
 		/* Copy over the block header verbatim. It's not compressed. */
 		memcpy(uncompressed, block->data, block_header_skip);
@@ -212,16 +215,19 @@ int block_reader_init(struct block_reader *br, struct reftable_block *block,
 		if (Z_OK !=
 		    uncompress2(uncompressed + block_header_skip, &dst_len,
 				block->data + block_header_skip, &src_len)) {
-			reftable_free(uncompressed);
+			err = REFTABLE_ZLIB_ERROR;
-			return REFTABLE_ZLIB_ERROR;
+			goto done;
 		}
 
-		if (dst_len + block_header_skip != sz)
+		if (dst_len + block_header_skip != sz) {
-			return REFTABLE_FORMAT_ERROR;
+			err = REFTABLE_FORMAT_ERROR;
+			goto done;
+		}
 
 		/* We're done with the input data. */
 		reftable_block_done(block);
 		block->data = uncompressed;
+		uncompressed = NULL;
 		block->len = sz;
 		block->source = malloc_block_source();
 		full_block_size = src_len + block_header_skip;
@@ -251,7 +257,9 @@ int block_reader_init(struct block_reader *br, struct reftable_block *block,
 	br->restart_count = restart_count;
 	br->restart_bytes = restart_bytes;
 
-	return 0;
+done:
+	reftable_free(uncompressed);
+	return err;
 }
 
 static uint32_t block_reader_restart_offset(struct block_reader *br, int i)

reftable/reader.c

@@ -290,28 +290,33 @@ int reader_init_block_reader(struct reftable_reader *r, struct block_reader *br,
 
 	err = reader_get_block(r, &block, next_off, guess_block_size);
 	if (err < 0)
-		return err;
+		goto done;
 
 	block_size = extract_block_size(block.data, &block_typ, next_off,
 					r->version);
-	if (block_size < 0)
+	if (block_size < 0) {
-		return block_size;
+		err = block_size;
-
+		goto done;
+	}
 	if (want_typ != BLOCK_TYPE_ANY && block_typ != want_typ) {
-		reftable_block_done(&block);
+		err = 1;
-		return 1;
+		goto done;
 	}
 
 	if (block_size > guess_block_size) {
 		reftable_block_done(&block);
 		err = reader_get_block(r, &block, next_off, block_size);
 		if (err < 0) {
-			return err;
+			goto done;
 		}
 	}
 
-	return block_reader_init(br, &block, header_off, r->block_size,
+	err = block_reader_init(br, &block, header_off, r->block_size,
-				 hash_size(r->hash_id));
+				hash_size(r->hash_id));
+done:
+	reftable_block_done(&block);
+
+	return err;
 }
 
 static int table_iter_next_block(struct table_iter *dest,

reftable/readwrite_test.c

@@ -254,6 +254,71 @@ static void test_log_write_read(void)
 	reader_close(&rd);
 }
 
+static void test_log_zlib_corruption(void)
+{
+	struct reftable_write_options opts = {
+		.block_size = 256,
+	};
+	struct reftable_iterator it = { 0 };
+	struct reftable_reader rd = { 0 };
+	struct reftable_block_source source = { 0 };
+	struct strbuf buf = STRBUF_INIT;
+	struct reftable_writer *w =
+		reftable_new_writer(&strbuf_add_void, &buf, &opts);
+	const struct reftable_stats *stats = NULL;
+	uint8_t hash1[GIT_SHA1_RAWSZ] = { 1 };
+	uint8_t hash2[GIT_SHA1_RAWSZ] = { 2 };
+	char message[100] = { 0 };
+	int err, i, n;
+
+	struct reftable_log_record log = {
+		.refname = "refname",
+		.value_type = REFTABLE_LOG_UPDATE,
+		.value = {
+			.update = {
+				.new_hash = hash1,
+				.old_hash = hash2,
+				.name = "My Name",
+				.email = "myname@invalid",
+				.message = message,
+			},
+		},
+	};
+
+	for (i = 0; i < sizeof(message) - 1; i++)
+		message[i] = (uint8_t)(rand() % 64 + ' ');
+
+	reftable_writer_set_limits(w, 1, 1);
+
+	err = reftable_writer_add_log(w, &log);
+	EXPECT_ERR(err);
+
+	n = reftable_writer_close(w);
+	EXPECT(n == 0);
+
+	stats = writer_stats(w);
+	EXPECT(stats->log_stats.blocks > 0);
+	reftable_writer_free(w);
+	w = NULL;
+
+	/* corrupt the data. */
+	buf.buf[50] ^= 0x99;
+
+	block_source_from_strbuf(&source, &buf);
+
+	err = init_reader(&rd, &source, "file.log");
+	EXPECT_ERR(err);
+
+	err = reftable_reader_seek_log(&rd, &it, "refname");
+	EXPECT(err == REFTABLE_ZLIB_ERROR);
+
+	reftable_iterator_destroy(&it);
+
+	/* cleanup. */
+	strbuf_release(&buf);
+	reader_close(&rd);
+}
+
 static void test_table_read_write_sequential(void)
 {
 	char **names;
@@ -633,6 +698,7 @@ static void test_corrupt_table(void)
 
 int readwrite_test_main(int argc, const char *argv[])
 {
+	RUN_TEST(test_log_zlib_corruption);
 	RUN_TEST(test_corrupt_table);
 	RUN_TEST(test_corrupt_table_empty);
 	RUN_TEST(test_log_write_read);