btrfs-progs: tests: add fuzzing of superblock

Use btrfs-sb-mod and do some arbitrary changes to super blocks. Then run
'btrfs check'. Check will fail to read the filesystem most of the time
and cannot do any actual repair but must not crash.

Signed-off-by: David Sterba <dsterba@suse.com>

Makefile

@@ -550,7 +550,7 @@ test-mkfs: btrfs mkfs.btrfs
 	@echo "    [TEST]   mkfs-tests.sh"
 	$(Q)bash tests/mkfs-tests.sh
 
-test-fuzz: btrfs btrfs-image
+test-fuzz: btrfs btrfs-image btrfs-sb-mod
 	@echo "    [TEST]   fuzz-tests.sh"
 	$(Q)bash tests/fuzz-tests.sh
 

tests/common

@@ -410,7 +410,7 @@ check_prereq()
 {
 	# Internal tools for testing, not shipped with the package
 	case "$1" in
-	btrfs-corrupt-block|btrfs-find-root|btrfs-select-super|fssum)
+	btrfs-corrupt-block|btrfs-find-root|btrfs-select-super|fssum|btrfs-sb-mod)
 		if ! [ -f "$INTERNAL_BIN/$1" ]; then
 			_fail "Failed prerequisites: $INTERNAL_BIN/$1";
 		fi

tests/fuzz-tests/010-simple-sb/test.sh

@@ -0,0 +1,68 @@
+#!/bin/bash
+# Change fields in super block and do test run of 'btrfs check'
+
+source "$TEST_TOP/common" || exit
+source "$TEST_TOP/common.convert" || exit
+
+check_prereq btrfs-sb-mod
+
+setup_root_helper
+prepare_test_dev
+
+run_check_mkfs_test_dev
+run_check_mount_test_dev
+#populate_fs
+generate_dataset "small"
+generate_dataset "sparse"
+run_check_umount_test_dev
+
+# See btrfs-sb-mod --help
+fields=(
+bytenr
+flags
+magic
+generation
+root
+chunk_root
+log_root
+total_bytes
+bytes_used
+root_dir_objectid
+num_devices
+sectorsize
+nodesize
+stripesize
+sys_chunk_array_size
+chunk_root_generation
+compat_flags
+compat_ro_flags
+incompat_flags
+csum_type
+root_level
+chunk_root_level
+log_root_level
+cache_generation
+uuid_tree_generation
+dev_item.devid
+dev_item.total_bytes
+dev_item.bytes_used
+dev_item.io_align
+dev_item.io_width
+dev_item.sector_size
+dev_item.type
+dev_item.generation
+dev_item.start_offset
+dev_item.dev_group
+dev_item.seek_speed
+dev_item.bandwidth)
+
+for field in "${fields[@]}"; do
+	for op in -1 +1 ^2 ^4 ^256 +4096 -4096 @; do
+		run_check $SUDO_HELPER truncate -s 0 image.test
+		run_check $SUDO_HELPER cp --reflink=auto --sparse=auto "$TEST_DEV" image.test
+		run_check $SUDO_HELPER "$TOP/btrfs-sb-mod" image.test "$field" "$op"
+		run_mayfail $SUDO_HELPER "$TOP/btrfs" check image.test
+	done
+done
+
+run_check $SUDO_HELPER rm -f -- image.test