linux-kernel - [PATCH 3/4] selftests/memfd: add tests for F_SEAL

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Date:   Fri,  1 Apr 2022 15:08:33 -0700
From:   Daniel Verkamp <dverkamp@...omium.org>
To:     linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Mattias Nissler <mnissler@...omium.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Daniel Verkamp <dverkamp@...omium.org>
Subject: [PATCH 3/4] selftests/memfd: add tests for F_SEAL_EXEC

Basic tests to ensure that user/group/other execute bits cannot be
changed after applying F_SEAL_EXEC to a memfd.

Signed-off-by: Daniel Verkamp <dverkamp@...omium.org>
---
 tools/testing/selftests/memfd/memfd_test.c | 80 ++++++++++++++++++++++
 1 file changed, 80 insertions(+)

diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c
index 94df2692e6e4..fdb0e46e9df9 100644
--- a/tools/testing/selftests/memfd/memfd_test.c
+++ b/tools/testing/selftests/memfd/memfd_test.c
@@ -28,6 +28,10 @@
 #define MFD_DEF_SIZE 8192
 #define STACK_SIZE 65536
 
+#ifndef F_SEAL_EXEC
+#define F_SEAL_EXEC	0x0020
+#endif
+
 /*
  * Default is not to test hugetlbfs
  */
@@ -594,6 +598,48 @@ static void mfd_fail_grow_write(int fd)
 	}
 }
 
+static void mfd_assert_mode(int fd, int mode)
+{
+	struct stat st;
+
+	if (fstat(fd, &st) < 0) {
+		printf("fstat(%d) failed: %m\n", fd);
+		abort();
+	} else if ((st.st_mode & 07777) != mode) {
+		printf("wrong file mode 0%04o, but expected 0%04o\n",
+		       (int)st.st_mode & 07777, mode);
+		abort();
+	}
+}
+
+static void mfd_assert_chmod(int fd, int mode)
+{
+	if (fchmod(fd, mode) < 0) {
+		printf("fchmod(0%04o) failed: %m\n", mode);
+		abort();
+	}
+
+	mfd_assert_mode(fd, mode);
+}
+
+static void mfd_fail_chmod(int fd, int mode)
+{
+	struct stat st;
+
+	if (fstat(fd, &st) < 0) {
+		printf("fstat(%d) failed: %m\n", fd);
+		abort();
+	}
+
+	if (fchmod(fd, mode) == 0) {
+		printf("fchmod(0%04o) didn't fail as expected\n");
+		abort();
+	}
+
+	/* verify that file mode bits did not change */
+	mfd_assert_mode(fd, st.st_mode & 07777);
+}
+
 static int idle_thread_fn(void *arg)
 {
 	sigset_t set;
@@ -880,6 +926,39 @@ static void test_seal_resize(void)
 	close(fd);
 }
 
+/*
+ * Test SEAL_EXEC
+ * Test that chmod() cannot change x bits after sealing
+ */
+static void test_seal_exec(void)
+{
+	int fd;
+
+	printf("%s SEAL-EXEC\n", memfd_str);
+
+	fd = mfd_assert_new("kern_memfd_seal_exec",
+			    mfd_def_size,
+			    MFD_CLOEXEC | MFD_ALLOW_SEALING);
+
+	mfd_assert_mode(fd, 0777);
+
+	mfd_assert_chmod(fd, 0644);
+
+	mfd_assert_has_seals(fd, 0);
+	mfd_assert_add_seals(fd, F_SEAL_EXEC);
+	mfd_assert_has_seals(fd, F_SEAL_EXEC);
+
+	mfd_assert_chmod(fd, 0600);
+	mfd_fail_chmod(fd, 0777);
+	mfd_fail_chmod(fd, 0670);
+	mfd_fail_chmod(fd, 0605);
+	mfd_fail_chmod(fd, 0700);
+	mfd_fail_chmod(fd, 0100);
+	mfd_assert_chmod(fd, 0666);
+
+	close(fd);
+}
+
 /*
  * Test sharing via dup()
  * Test that seals are shared between dupped FDs and they're all equal.
@@ -1059,6 +1138,7 @@ int main(int argc, char **argv)
 	test_seal_shrink();
 	test_seal_grow();
 	test_seal_resize();
+	test_seal_exec();
 
 	test_share_dup("SHARE-DUP", "");
 	test_share_mmap("SHARE-MMAP", "");
-- 
2.35.1.1094.g7c7d902a7c-goog