[PATCH v5] kconfig: warn about malformed KCONFIG_PROBABILITY values

[Dmitrii Tulnov <tulnov.dl@gmail.com>]

randconfig checks the numeric range of each probability but does not
validate where strtol() stops. For example, KCONFIG_PROBABILITY=50% is
accepted as 50:0:0: the '%' is parsed repeatedly as zero. For the
documented value 50, tristate y/m/n probabilities are 25%/25%/50%.
With 50%, both y/m probabilities silently become zero, reducing the
coverage of random configuration builds. Empty fields and extra fields
are also accepted.

Warn when the value does not follow the documented decimal format. For
malformed inputs whose parsed probabilities are in range, preserve the
existing interpretation unless KCONFIG_WERROR is set. In that case, exit
with an error before writing the configuration. Leading whitespace and
signs are accepted by strtol(), but also trigger the warning because they
are outside the documented format.

Keep the strtol() result as long until the range check. This rejects
out-of-range values that narrowing to int previously made valid, such as
4294967296 becoming zero on a 64-bit host, regardless of KCONFIG_WERROR.

Add regression tests for one warning per malformed input, preserved
configurations, KCONFIG_WERROR, out-of-range values, the supported
probability formats, and the documented empty-value default.

Fixes: e43956e60769 ("kconfig: implement KCONFIG_PROBABILITY for randconfig")
Assisted-by: LLM
Signed-off-by: Dmitrii Tulnov <tulnov.dl@gmail.com>
---
Thanks, Julian. I've replaced the parametrization with loops and removed
the unused pytest import. All input combinations and checks are preserved.
Assertion messages identify the failing input and, where applicable, the
seed and KCONFIG_WERROR value. Each test function now stops at its first
failing case.

Changes since v4:
- Replace pytest.mark.parametrize with loops and remove the unused pytest
  import from the probability test module, as requested by Julian.
- Include the probability and, where applicable, seed and WERROR value in
  assertion messages. Preserve all input combinations and checks.

Changes since v3:
- Move the KCONFIG_WERROR cleanup fixture to the shared conftest.py,
  as requested by Julian. Explicit extra_env settings still enable WERROR.

Changes since v2:
- Move the expected tristate distribution into the problem description.
- Simplify the initial format check to !isdigit((unsigned char)*env).
- Pass probability values and seeds through conf._run_conf(extra_env=...).
  Use monkeypatch.delenv only to remove inherited variables.
- Add -0, +0, bare + and - warning cases, and the +101 range-error case.
- Honor KCONFIG_WERROR for malformed format warnings, as discussed with
  Julian. Check unset, empty, 0 and 1 flag behavior.
- Compare 50% with 50:0:0 and -0 with 0 across 20 fixed seeds and check
  that each malformed input produces exactly one warning.
- Clarify that compatibility applies to malformed in-range inputs with
  KCONFIG_WERROR unset; values previously accepted by narrowing now fail.

Changes since v1:
- Warn about malformed in-range values while retaining their previous
  interpretation by default.
- Warn about leading whitespace and signs as undocumented input.
- Clarify that 50 gives tristate y/m/n probabilities of 25%/25%/50%, and
  compare it with the equivalent input 50:25:25 across 20 fixed seeds.

Validation on kbuild-next, x86_64, GCC 13.3.0:
- make testconfig with HOSTCFLAGS=-Werror: 28 passed, both normally and
  with KCONFIG_WERROR=1 inherited from the test runner. Explicit strict
  cases for empty, 0 and 1 flag values still pass.
- The same suite passed on the existing ASan/UBSan build at -O1, with
  leak detection disabled: 28 passed in each environment.
- The probability module now reports 7 tests instead of 117. Tracing
  confirms that all 178 actual conf calls match v4 in order, inputs,
  exit status, stdout, stderr and generated configuration.
- The new suite gives 4 expected failures and 24 passes on the original
  binary; the version before WERROR gives 1 expected failure and 27
  passes. Loops stop at their first failure, so these counts differ
  from the earlier parametrized regression results.
- C code, test Kconfig and shared fixtures are unchanged from v4.
  Earlier C compatibility and file-preservation checks were not rerun.
- No vmlinux build or boot test; this changes the host configuration tool.
  32-bit hosts and other libc implementations were not tested.

 scripts/kconfig/conf.c                        |  16 +-
 scripts/kconfig/tests/conftest.py             |   6 +
 .../tests/randconfig_probability/Kconfig      |  12 ++
 .../tests/randconfig_probability/__init__.py  | 139 ++++++++++++++++++
 4 files changed, 172 insertions(+), 1 deletion(-)
 create mode 100644 scripts/kconfig/tests/randconfig_probability/Kconfig
 create mode 100644 scripts/kconfig/tests/randconfig_probability/__init__.py

diff --git a/scripts/kconfig/conf.c b/scripts/kconfig/conf.c
index fe8ba09b0..ca6d9d735 100644
--- a/scripts/kconfig/conf.c
+++ b/scripts/kconfig/conf.c
@@ -186,12 +186,23 @@ static void conf_set_all_new_symbols(enum conf_def_mode mode)
 
 	if (mode == def_random) {
 		int n, p[3];
+		bool warned = false;
 		char *env = getenv("KCONFIG_PROBABILITY");
 
 		n = 0;
 		while (env && *env) {
 			char *endp;
-			int tmp = strtol(env, &endp, 10);
+			long tmp = strtol(env, &endp, 10);
+
+			if (!isdigit((unsigned char)*env) ||
+			    (*endp && *endp != ':') ||
+			    (*endp == ':' && (!endp[1] || n == 2))) {
+				if (!warned) {
+					fprintf(stderr,
+						"warning: KCONFIG_PROBABILITY has malformed format\n");
+					warned = true;
+				}
+			}
 
 			if (tmp >= 0 && tmp <= 100) {
 				p[n++] = tmp;
@@ -227,6 +238,9 @@ static void conf_set_all_new_symbols(enum conf_def_mode mode)
 			perror("KCONFIG_PROBABILITY");
 			exit(1);
 		}
+
+		if (warned && getenv("KCONFIG_WERROR"))
+			exit(1);
 	}
 
 	menu_for_each_entry(menu) {
diff --git a/scripts/kconfig/tests/conftest.py b/scripts/kconfig/tests/conftest.py
index 66f95e4ed..2263bd2a3 100644
--- a/scripts/kconfig/tests/conftest.py
+++ b/scripts/kconfig/tests/conftest.py
@@ -312,6 +312,12 @@ class Conf:
         return self._matches('stderr', expected)
 
 
+@pytest.fixture(autouse=True)
+def clear_werror(monkeypatch):
+    # extra_env can set strict mode, but cannot remove an inherited flag.
+    monkeypatch.delenv('KCONFIG_WERROR', raising=False)
+
+
 @pytest.fixture(scope="module")
 def conf(request):
     """Create a Conf instance and provide it to test functions."""
diff --git a/scripts/kconfig/tests/randconfig_probability/Kconfig b/scripts/kconfig/tests/randconfig_probability/Kconfig
new file mode 100644
index 000000000..84f4e5fcc
--- /dev/null
+++ b/scripts/kconfig/tests/randconfig_probability/Kconfig
@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+config MODULES
+	bool
+	default y
+	modules
+
+config BOOL
+	bool "Bool"
+
+config TRI
+	tristate "Tristate"
diff --git a/scripts/kconfig/tests/randconfig_probability/__init__.py b/scripts/kconfig/tests/randconfig_probability/__init__.py
new file mode 100644
index 000000000..5f9c90e17
--- /dev/null
+++ b/scripts/kconfig/tests/randconfig_probability/__init__.py
@@ -0,0 +1,139 @@
+# SPDX-License-Identifier: GPL-2.0-only
+"""Validate KCONFIG_PROBABILITY without changing the supported distributions."""
+
+
+def test_malformed_warns(conf):
+    probabilities = [
+        'invalid', ' ', '50%', '50 ', '0x32', '10 20', '10:20x',
+        '10:20:invalid', '10:20:30x',
+        ':50', '50:', '10::20', '10:20:', '10:20:30:', '10:20:30:40',
+        '-0', '+0', '+', '-', '+100:0', ' \t100:0', '0: \t100:0',
+    ]
+    for probability in probabilities:
+        assert conf._run_conf('--randconfig', extra_env={
+            'KCONFIG_PROBABILITY': probability,
+            'KCONFIG_SEED': '0',
+        }) == 0, repr(probability)
+        assert ('warning: KCONFIG_PROBABILITY has malformed format' in
+                conf.stderr), repr(probability)
+        assert conf.stderr.count('warning:') == 1, repr(probability)
+        assert conf.config is not None, repr(probability)
+
+
+def test_malformed_preserves_config(conf):
+    probabilities = [('50%', '50:0:0'), ('-0', '0')]
+    for seed in range(20):
+        for probability, equivalent in probabilities:
+            context = 'probability={!r}, equivalent={!r}, seed={}'.format(
+                probability, equivalent, seed)
+            assert conf._run_conf('--randconfig', extra_env={
+                'KCONFIG_PROBABILITY': probability,
+                'KCONFIG_SEED': hex(seed),
+            }) == 0, context
+            assert ('warning: KCONFIG_PROBABILITY has malformed format' in
+                    conf.stderr), context
+            assert conf.stderr.count('warning:') == 1, context
+            malformed = conf.config
+
+            assert conf._run_conf('--randconfig', extra_env={
+                'KCONFIG_PROBABILITY': equivalent,
+                'KCONFIG_SEED': hex(seed),
+            }) == 0, context
+            assert 'warning:' not in conf.stderr, context
+            assert conf.config == malformed, context
+
+
+def test_werror(conf):
+    probabilities = [
+        ('', 0), ('50', 0), ('50%', 1), ('-0', 1), ('10:20:30:40', 1),
+    ]
+    for probability, status in probabilities:
+        for werror in ['', '0', '1']:
+            context = 'probability={!r}, werror={!r}'.format(
+                probability, werror)
+            assert conf._run_conf('--randconfig', extra_env={
+                'KCONFIG_PROBABILITY': probability,
+                'KCONFIG_SEED': '0',
+                'KCONFIG_WERROR': werror,
+            }) == status, context
+            if status:
+                assert ('warning: KCONFIG_PROBABILITY has malformed format' in
+                        conf.stderr), context
+                assert conf.stderr.count('warning:') == 1, context
+            else:
+                assert 'warning:' not in conf.stderr, context
+
+
+def test_out_of_range(conf):
+    probabilities = [
+        '-1', '101', '+101', '0:101', '0:0:101', '60:41', '0:60:41',
+        '4294967296', '-4294967296',
+        '999999999999999999999999', '-999999999999999999999999',
+    ]
+    for probability in probabilities:
+        assert conf._run_conf('--randconfig', extra_env={
+            'KCONFIG_PROBABILITY': probability,
+            'KCONFIG_SEED': '0',
+        }) == 1, repr(probability)
+        assert 'KCONFIG_PROBABILITY:' in conf.stderr, repr(probability)
+
+
+def test_valid(conf):
+    probabilities = [
+        ('0', 'n', 'n'),
+        ('0:0', 'n', 'n'),
+        ('100:0', 'y', 'y'),
+        ('0:100', 'y', 'm'),
+        ('100:0:0', 'y', 'n'),
+        ('0:100:0', 'n', 'y'),
+        ('0:0:100', 'n', 'm'),
+        ('000:000:100', 'n', 'm'),
+    ]
+    for probability, boolean, tristate in probabilities:
+        assert conf._run_conf('--randconfig', extra_env={
+            'KCONFIG_PROBABILITY': probability,
+            'KCONFIG_SEED': '0',
+        }) == 0, repr(probability)
+        assert 'warning:' not in conf.stderr, repr(probability)
+        for symbol, value in [('BOOL', boolean), ('TRI', tristate)]:
+            if value == 'n':
+                expected = '# CONFIG_{} is not set'.format(symbol)
+            else:
+                expected = 'CONFIG_{}={}'.format(symbol, value)
+            assert expected in conf.config.splitlines(), repr(probability)
+
+
+def test_single_probability_matches_tristate_split(conf):
+    for seed in range(20):
+        context = 'seed={}'.format(seed)
+        assert conf._run_conf('--randconfig', extra_env={
+            'KCONFIG_PROBABILITY': '50',
+            'KCONFIG_SEED': hex(seed),
+        }) == 0, context
+        assert 'warning:' not in conf.stderr, context
+        single = conf.config
+
+        # 50% boolean y; 25% tristate y, 25% m, and 50% n.
+        assert conf._run_conf('--randconfig', extra_env={
+            'KCONFIG_PROBABILITY': '50:25:25',
+            'KCONFIG_SEED': hex(seed),
+        }) == 0, context
+        assert 'warning:' not in conf.stderr, context
+        assert conf.config == single, context
+
+
+def test_empty(conf, monkeypatch):
+    # extra_env overrides inherited variables, but cannot remove them.
+    monkeypatch.delenv('KCONFIG_PROBABILITY', raising=False)
+    assert conf._run_conf('--randconfig', extra_env={
+        'KCONFIG_SEED': '0',
+    }) == 0
+    assert 'warning:' not in conf.stderr
+    default_config = conf.config
+
+    assert conf._run_conf('--randconfig', extra_env={
+        'KCONFIG_PROBABILITY': '',
+        'KCONFIG_SEED': '0',
+    }) == 0
+    assert 'warning:' not in conf.stderr
+    assert conf.config == default_config

base-commit: cee9395acd8043be0644b25c34bfa86623f2b935