[PATCH v2 2/2] test/py: cover get_basename crash on paths with dotted directories

[Aristo Chen <aristo.chen@canonical.com>]

Add a parametrized regression test for the fix in the previous commit.
The test invokes mkimage in auto-FIT mode (-f auto) with a -b argument
whose directory component contains a '.' and whose leaf either lacks an
extension or is a plain identifier. Before the fix these inputs caused
get_basename() to compute a negative length and segfault inside memcpy.
The test asserts that mkimage exits successfully and that the fdt
sub-image description matches the expected stripped basename, covering
"./mydt", "./sub.d/leaf", and "./a.b/c". A control input of "./mydt.dtb"
is also exercised to confirm normal extension stripping still works.

Signed-off-by: Aristo Chen <aristo.chen@canonical.com>
---
 test/py/tests/test_fit_mkimage_validate.py | 57 ++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/test/py/tests/test_fit_mkimage_validate.py b/test/py/tests/test_fit_mkimage_validate.py
index 170b2a8cbbb..5922f071dd8 100644
--- a/test/py/tests/test_fit_mkimage_validate.py
+++ b/test/py/tests/test_fit_mkimage_validate.py
@@ -7,6 +7,7 @@ import os
 import subprocess
 import pytest
 import fit_util
+import utils
 import re
 
 @pytest.mark.boardspec('sandbox')
@@ -103,3 +104,59 @@ def test_fit_invalid_default_config(ubman):
 
     assert result.returncode != 0, "mkimage should fail due to missing default config"
     assert re.search(r"Default configuration '.*' not found under /configurations", result.stderr)
+
+@pytest.mark.boardspec('sandbox')
+@pytest.mark.requiredtool('dtc')
+@pytest.mark.requiredtool('fdtget')
+@pytest.mark.parametrize('dtb_relpath,expected_desc', [
+    # Crash triggers: last '.' precedes last '/', or leaf has no extension.
+    ('./mydt',       'mydt'),
+    ('./sub.d/leaf', 'leaf'),
+    ('./a.b/c',      'c'),
+    # Control case: extension lives in the leaf, no dotted directory.
+    ('./mydt.dtb',   'mydt'),
+])
+def test_fit_auto_basename_dotted_directory(ubman, dtb_relpath, expected_desc):
+    """Regression test: mkimage -f auto must not crash when a -b path has a
+    '.' in its directory portion.
+
+    Before the fix, get_basename() in tools/fit_image.c searched the whole
+    path for both the last '/' and the last '.'. When the '.' fell before
+    the '/', the computed length went negative and was passed unchanged to
+    memcpy(), which segfaulted. This test exercises three crashing paths
+    plus one control input.
+    """
+    build_dir = ubman.config.build_dir
+    kernel = fit_util.make_kernel(ubman, 'kernel.bin', 'kernel')
+    itb_fname = fit_util.make_fname(ubman, 'auto_basename.itb')
+
+    # Materialize the dtb at the requested relative path inside build_dir.
+    dtb_abs = os.path.join(build_dir, dtb_relpath)
+    os.makedirs(os.path.dirname(dtb_abs), exist_ok=True)
+    with open(dtb_abs, 'wb') as f:
+        f.write(b'dummy')
+
+    cmd = ['./tools/mkimage', '-f', 'auto',
+           '-A', 'arm', '-O', 'linux', '-T', 'kernel', '-C', 'none',
+           '-a', '0x80000000', '-e', '0x80000000', '-n', 'test',
+           '-d', kernel,
+           '-b', dtb_relpath,
+           itb_fname]
+    # Run with cwd=build_dir so both ./tools/mkimage and the relative -b
+    # path resolve the same way the bug originally reproduced.
+    result = subprocess.run(cmd, capture_output=True, text=True,
+                            cwd=build_dir)
+
+    assert result.returncode == 0, (
+        f"mkimage crashed or failed on -b {dtb_relpath!r}: "
+        f"rc={result.returncode}\nstdout:\n{result.stdout}\n"
+        f"stderr:\n{result.stderr}"
+    )
+    # The fdt sub-image description is set from get_basename(). Read it back
+    # from the produced FIT (a device tree) rather than parsing mkimage's
+    # console output.
+    desc = utils.run_and_log(
+        ubman, ['fdtget', itb_fname, '/images/fdt-1', 'description']).strip()
+    assert desc == expected_desc, (
+        f"Expected /images/fdt-1 description {expected_desc!r}, got {desc!r}"
+    )
-- 
2.43.0