[PATCH 1/2] exec: Add KUnit test for bprm_stack_limits()
From: Kees Cook
Date: Sun May 19 2024 - 22:16:45 EST
Since bprm_stack_limits() operates with very limited side-effects, add
it as the first exec.c KUnit test. Add to Kconfig and adjust MAINTAINERS
file to include it.
Tested on 64-bit UML:
$ tools/testing/kunit/kunit.py run exec
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Justin Stitt <justinstitt@xxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
---
MAINTAINERS | 2 +
fs/Kconfig.binfmt | 8 ++++
fs/exec.c | 13 ++++++
fs/exec_test.c | 113 ++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 136 insertions(+)
create mode 100644 fs/exec_test.c
diff --git a/MAINTAINERS b/MAINTAINERS
index 7c121493f43d..845165dbb756 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8039,7 +8039,9 @@ S: Supported
T: git git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/execve
F: Documentation/userspace-api/ELF.rst
F: fs/*binfmt_*.c
+F: fs/Kconfig.binfmt
F: fs/exec.c
+F: fs/exec_test.c
F: include/linux/binfmts.h
F: include/linux/elf.h
F: include/uapi/linux/binfmts.h
diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
index f5693164ca9a..58657f2d9719 100644
--- a/fs/Kconfig.binfmt
+++ b/fs/Kconfig.binfmt
@@ -176,4 +176,12 @@ config COREDUMP
certainly want to say Y here. Not necessary on systems that never
need debugging or only ever run flawless code.
+config EXEC_KUNIT_TEST
+ bool "Build execve tests" if !KUNIT_ALL_TESTS
+ depends on KUNIT
+ default KUNIT_ALL_TESTS
+ help
+ This builds the exec KUnit tests, which tests boundary conditions
+ of various aspects of the exec internals.
+
endmenu
diff --git a/fs/exec.c b/fs/exec.c
index b3c40fbb325f..1d45e1a2d620 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -475,6 +475,15 @@ static int count_strings_kernel(const char *const *argv)
return i;
}
+/*
+ * Calculate bprm->argmin from:
+ * - _STK_LIM
+ * - ARG_MAX
+ * - bprm->rlim_stack.rlim_cur
+ * - bprm->argc
+ * - bprm->envc
+ * - bprm->p
+ */
static int bprm_stack_limits(struct linux_binprm *bprm)
{
unsigned long limit, ptr_size;
@@ -2200,3 +2209,7 @@ static int __init init_fs_exec_sysctls(void)
fs_initcall(init_fs_exec_sysctls);
#endif /* CONFIG_SYSCTL */
+
+#ifdef CONFIG_EXEC_KUNIT_TEST
+#include "exec_test.c"
+#endif
diff --git a/fs/exec_test.c b/fs/exec_test.c
new file mode 100644
index 000000000000..32a90c6f47e7
--- /dev/null
+++ b/fs/exec_test.c
@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <kunit/test.h>
+
+struct bprm_stack_limits_result {
+ struct linux_binprm bprm;
+ int expected_rc;
+ unsigned long expected_argmin;
+};
+
+static const struct bprm_stack_limits_result bprm_stack_limits_results[] = {
+ /* Giant values produce -E2BIG */
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ULONG_MAX,
+ .argc = INT_MAX, .envc = INT_MAX }, .expected_rc = -E2BIG },
+ /*
+ * 0 rlim_stack will get raised to ARG_MAX. With 1 string pointer,
+ * we should see p - ARG_MAX + sizeof(void *).
+ */
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0,
+ .argc = 1, .envc = 0 }, .expected_argmin = ULONG_MAX - ARG_MAX + sizeof(void *)},
+ /* Validate that argc is always raised to a minimum of 1. */
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0,
+ .argc = 0, .envc = 0 }, .expected_argmin = ULONG_MAX - ARG_MAX + sizeof(void *)},
+ /*
+ * 0 rlim_stack will get raised to ARG_MAX. With pointers filling ARG_MAX,
+ * we should see -E2BIG. (Note argc is always raised to at least 1.)
+ */
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0,
+ .argc = ARG_MAX / sizeof(void *), .envc = 0 }, .expected_rc = -E2BIG },
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0,
+ .argc = 0, .envc = ARG_MAX / sizeof(void *) - 1 }, .expected_rc = -E2BIG },
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0,
+ .argc = ARG_MAX / sizeof(void *) + 1, .envc = 0 }, .expected_rc = -E2BIG },
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0,
+ .argc = 0, .envc = ARG_MAX / sizeof(void *) }, .expected_rc = -E2BIG },
+ /* And with one less, we see space for exactly 1 pointer. */
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0,
+ .argc = (ARG_MAX / sizeof(void *)) - 1, .envc = 0 },
+ .expected_argmin = ULONG_MAX - sizeof(void *) },
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 0,
+ .argc = 0, .envc = (ARG_MAX / sizeof(void *)) - 2, },
+ .expected_argmin = ULONG_MAX - sizeof(void *) },
+ /* If we raise rlim_stack / 4 to exactly ARG_MAX, nothing changes. */
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ARG_MAX * 4,
+ .argc = ARG_MAX / sizeof(void *), .envc = 0 }, .expected_rc = -E2BIG },
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ARG_MAX * 4,
+ .argc = 0, .envc = ARG_MAX / sizeof(void *) - 1 }, .expected_rc = -E2BIG },
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ARG_MAX * 4,
+ .argc = ARG_MAX / sizeof(void *) + 1, .envc = 0 }, .expected_rc = -E2BIG },
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ARG_MAX * 4,
+ .argc = 0, .envc = ARG_MAX / sizeof(void *) }, .expected_rc = -E2BIG },
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ARG_MAX * 4,
+ .argc = (ARG_MAX / sizeof(void *)) - 1, .envc = 0 },
+ .expected_argmin = ULONG_MAX - sizeof(void *) },
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = ARG_MAX * 4,
+ .argc = 0, .envc = (ARG_MAX / sizeof(void *)) - 2, },
+ .expected_argmin = ULONG_MAX - sizeof(void *) },
+ /* But raising it another pointer * 4 will provide space for 1 more pointer. */
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = (ARG_MAX + sizeof(void *)) * 4,
+ .argc = ARG_MAX / sizeof(void *), .envc = 0 },
+ .expected_argmin = ULONG_MAX - sizeof(void *) },
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = (ARG_MAX + sizeof(void *)) * 4,
+ .argc = 0, .envc = ARG_MAX / sizeof(void *) - 1 },
+ .expected_argmin = ULONG_MAX - sizeof(void *) },
+ /* Raising rlim_stack / 4 to _STK_LIM / 4 * 3 will see more space. */
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 4 * (_STK_LIM / 4 * 3),
+ .argc = 0, .envc = 0 },
+ .expected_argmin = ULONG_MAX - (_STK_LIM / 4 * 3) + sizeof(void *) },
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 4 * (_STK_LIM / 4 * 3),
+ .argc = 0, .envc = 0 },
+ .expected_argmin = ULONG_MAX - (_STK_LIM / 4 * 3) + sizeof(void *) },
+ /* But raising it any further will see no increase. */
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 4 * (_STK_LIM / 4 * 3 + sizeof(void *)),
+ .argc = 0, .envc = 0 },
+ .expected_argmin = ULONG_MAX - (_STK_LIM / 4 * 3) + sizeof(void *) },
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 4 * (_STK_LIM / 4 * + sizeof(void *)),
+ .argc = 0, .envc = 0 },
+ .expected_argmin = ULONG_MAX - (_STK_LIM / 4 * 3) + sizeof(void *) },
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 4 * _STK_LIM,
+ .argc = 0, .envc = 0 },
+ .expected_argmin = ULONG_MAX - (_STK_LIM / 4 * 3) + sizeof(void *) },
+ { { .p = ULONG_MAX, .rlim_stack.rlim_cur = 4 * _STK_LIM,
+ .argc = 0, .envc = 0 },
+ .expected_argmin = ULONG_MAX - (_STK_LIM / 4 * 3) + sizeof(void *) },
+};
+
+static void exec_test_bprm_stack_limits(struct kunit *test)
+{
+ /* Double-check the constants. */
+ KUNIT_EXPECT_EQ(test, _STK_LIM, SZ_8M);
+ KUNIT_EXPECT_EQ(test, ARG_MAX, 32 * SZ_4K);
+
+ for (int i = 0; i < ARRAY_SIZE(bprm_stack_limits_results); i++) {
+ const struct bprm_stack_limits_result *result = &bprm_stack_limits_results[i];
+ struct linux_binprm bprm = result->bprm;
+ int rc;
+
+ rc = bprm_stack_limits(&bprm);
+ KUNIT_EXPECT_EQ_MSG(test, rc, result->expected_rc, "on loop %d", i);
+ KUNIT_EXPECT_EQ_MSG(test, bprm.argmin, result->expected_argmin, "on loop %d", i);
+ }
+}
+
+static struct kunit_case exec_test_cases[] = {
+ KUNIT_CASE(exec_test_bprm_stack_limits),
+ {},
+};
+
+static struct kunit_suite exec_test_suite = {
+ .name = "exec",
+ .test_cases = exec_test_cases,
+};
+
+kunit_test_suite(exec_test_suite);
--
2.34.1