update

tests/TC112-invalid-superblock.md

@@ -0,0 +1,56 @@
+# Test Case: Invalid Superblock Magic
+
+**Test ID**: TC112-invalid-superblock
+**Category**: Error Handling
+**Priority**: Critical
+
+## Objective
+
+Verify rejection of an invalid EROFS magic at the real field while provider
+length and all suffix bytes covered by repo22's production checksum verifier
+remain unchanged.
+
+## Fixture Qualification
+
+```sh
+work=$(mktemp -d /tmp/repo22-tc112.XXXXXX)
+tests/prepare_error_fixtures.sh "$work/fixtures"
+od -An -tx4 -j 1024 -N 4 "$work/fixtures/bad-magic.erofs"
+python3 tests/erofs_fixture.py inspect "$work/fixtures/bad-magic.erofs"
+grep '^bad-magic ' "$work/fixtures/fixture-evidence.txt"
+wc -c "$work/fixtures/valid-plain.erofs" \
+  "$work/fixtures/bad-magic.erofs"
+sha256 -q "$work/fixtures/bad-magic.erofs"
+```
+
+The mutator asserts magic `0xe0f5e1e2` at byte 1024 and replaces it with
+`0x21444142`. It intentionally leaves the stored checksum unchanged. The
+canonical checksum over the changed magic is invalid, but the production
+fixed-magic suffix calculation over `[1032,4096)` remains valid because no
+suffix byte changed. Magic validation occurs first.
+
+## FreeBSD Procedure
+
+```sh
+mkdir "$work/mnt"
+unit=$(mdconfig -a -t vnode -f "$work/fixtures/bad-magic.erofs")
+set +e
+mount -t erofs -o ro "/dev/$unit" "$work/mnt" \
+  >"$work/mount.out" 2>"$work/mount.err"
+status=$?
+set -e
+test "$status" -ne 0
+set +e
+truss -o "$work/mount.truss" mount -t erofs -o ro "/dev/$unit" \
+  "$work/mnt" >/dev/null 2>&1
+set -e
+grep -E 'nmount.*ERR#22' "$work/mount.truss"
+! mount -p | awk -v path="$work/mnt" '$2 == path { found=1 }
+  END { exit found ? 0 : 1 }'
+mdconfig -d -u "${unit#md}"
+```
+
+## Expected Results
+
+Mount returns errno 22 (`EINVAL`) before root vnode creation. No panic, mount,
+or md consumer remains.