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Subject[PATCH v3 2/2] selftests/memfd: Add tests for F_SEAL_FS_WRITE seal
Date
Add tests to verify sealing memfds with the F_SEAL_FS_WRITE works as
expected.

Cc: dancol@google.com
Cc: minchan@kernel.org
Reviewed-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
tools/testing/selftests/memfd/memfd_test.c | 74 ++++++++++++++++++++++
1 file changed, 74 insertions(+)

diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c
index 10baa1652fc2..32b207ca7372 100644
--- a/tools/testing/selftests/memfd/memfd_test.c
+++ b/tools/testing/selftests/memfd/memfd_test.c
@@ -692,6 +692,79 @@ static void test_seal_write(void)
close(fd);
}

+/*
+ * Test SEAL_FUTURE_WRITE
+ * Test whether SEAL_FUTURE_WRITE actually prevents modifications.
+ */
+static void test_seal_future_write(void)
+{
+ int fd;
+ void *p;
+
+ printf("%s SEAL-FUTURE-WRITE\n", memfd_str);
+
+ fd = mfd_assert_new("kern_memfd_seal_future_write",
+ mfd_def_size,
+ MFD_CLOEXEC | MFD_ALLOW_SEALING);
+
+ p = mfd_assert_mmap_shared(fd);
+
+ mfd_assert_has_seals(fd, 0);
+ /* Not adding grow/shrink seals makes the future write
+ * seal fail to get added
+ */
+ mfd_fail_add_seals(fd, F_SEAL_FUTURE_WRITE);
+
+ mfd_assert_add_seals(fd, F_SEAL_GROW);
+ mfd_assert_has_seals(fd, F_SEAL_GROW);
+
+ /* Should still fail since shrink seal has
+ * not yet been added
+ */
+ mfd_fail_add_seals(fd, F_SEAL_FUTURE_WRITE);
+
+ mfd_assert_add_seals(fd, F_SEAL_SHRINK);
+ mfd_assert_has_seals(fd, F_SEAL_GROW |
+ F_SEAL_SHRINK);
+
+ /* Now should succeed, also verifies that the seal
+ * could be added with an existing writable mmap
+ */
+ mfd_assert_add_seals(fd, F_SEAL_FUTURE_WRITE);
+ mfd_assert_has_seals(fd, F_SEAL_SHRINK |
+ F_SEAL_GROW |
+ F_SEAL_FUTURE_WRITE);
+
+ /* read should pass, writes should fail */
+ mfd_assert_read(fd);
+ mfd_fail_write(fd);
+
+ munmap(p, mfd_def_size);
+ close(fd);
+
+ /* Test adding all seals (grow, shrink, future write) at once */
+ fd = mfd_assert_new("kern_memfd_seal_future_write2",
+ mfd_def_size,
+ MFD_CLOEXEC | MFD_ALLOW_SEALING);
+
+ p = mfd_assert_mmap_shared(fd);
+
+ mfd_assert_has_seals(fd, 0);
+ mfd_assert_add_seals(fd, F_SEAL_SHRINK |
+ F_SEAL_GROW |
+ F_SEAL_FUTURE_WRITE);
+ mfd_assert_has_seals(fd, F_SEAL_SHRINK |
+ F_SEAL_GROW |
+ F_SEAL_FUTURE_WRITE);
+
+ /* read should pass, writes should fail */
+ mfd_assert_read(fd);
+ mfd_fail_write(fd);
+
+ munmap(p, mfd_def_size);
+ close(fd);
+}
+
/*
* Test SEAL_SHRINK
* Test whether SEAL_SHRINK actually prevents shrinking
@@ -945,6 +1018,7 @@ int main(int argc, char **argv)
test_basic();

test_seal_write();
+ test_seal_future_write();
test_seal_shrink();
test_seal_grow();
test_seal_resize();
--
2.19.1.331.ge82ca0e54c-goog
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