[PATCH v4 2/4] generic/574: corrupt btrfs merkle tree data

[Boris Burkov <boris@bur.io>]

generic/574 has tests for corrupting the merkle tree data stored by the
filesystem. Since btrfs uses a different scheme for storing this data,
the existing logic for corrupting it doesn't work out of the box. Adapt
it to properly corrupt btrfs merkle items.

This test relies on the btrfs implementation of fsverity in the patches
titled:
btrfs: initial fsverity support
btrfs: check verity for reads of inline extents and holes
btrfs: fallback to buffered io for verity files

A fix for fiemap in the patch titled:
btrfs: return whole extents in fiemap

and on btrfs-corrupt-block for corruption in the patches titled:
btrfs-progs: corrupt generic item data with btrfs-corrupt-block
btrfs-progs: expand corrupt_file_extent in btrfs-corrupt-block

Signed-off-by: Boris Burkov <boris@bur.io>
---
 common/verity     | 18 ++++++++++++++++++
 tests/generic/574 |  5 +++++
 2 files changed, 23 insertions(+)

diff --git a/common/verity b/common/verity
index d2c1ea24..1636e88b 100644
--- a/common/verity
+++ b/common/verity
@@ -315,6 +315,24 @@ _fsv_scratch_corrupt_merkle_tree()
 		(( offset += ($(_get_filesize $file) + 65535) & ~65535 ))
 		_fsv_scratch_corrupt_bytes $file $offset
 		;;
+	btrfs)
+		local ino=$(stat -c '%i' $file)
+		_scratch_unmount
+		local byte=""
+		while read -n 1 byte; do
+			if [ -z $byte ]; then
+				break
+			fi
+			local ascii=$(printf "%d" "'$byte'")
+			# This command will find a Merkle tree item for the inode (-I $ino,37,0)
+			# in the default filesystem tree (-r 5) and corrupt one byte (-b 1) at
+			# $offset (-o $offset) with the ascii representation of the byte we read
+			# (-v $ascii)
+			$BTRFS_CORRUPT_BLOCK_PROG -r 5 -I $ino,37,0 -v $ascii -o $offset -b 1 $SCRATCH_DEV
+			(( offset += 1 ))
+		done
+		_scratch_mount
+		;;
 	*)
 		_fail "_fsv_scratch_corrupt_merkle_tree() unimplemented on $FSTYP"
 		;;
diff --git a/tests/generic/574 b/tests/generic/574
index 1e296618..e4370dae 100755
--- a/tests/generic/574
+++ b/tests/generic/574
@@ -43,6 +43,11 @@ _scratch_mount
 fsv_orig_file=$SCRATCH_MNT/file
 fsv_file=$SCRATCH_MNT/file.fsv
 
+# utility needed for corrupting Merkle data itself in btrfs
+if [ $FSTYP == "btrfs" ]; then
+	_require_command "$BTRFS_CORRUPT_BLOCK_PROG" btrfs_corrupt_block
+fi
+
 setup_zeroed_file()
 {
 	local len=$1
-- 
2.30.2