[PATCH v2 2/2] selftests/memfd: Add tests for F_SEAL_FS_WRITE seal

[Joel Fernandes (Google)]

Add tests to verify sealing memfds with the F_SEAL_FS_WRITE works as
expected.

Cc: dan...@google.com
Cc: minc...@google.com
Signed-off-by: Joel Fernandes (Google) <j...@joelfernandes.org>
---
 tools/testing/selftests/memfd/memfd_test.c | 51 +++++++++++++++++++++-
 1 file changed, 50 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/memfd/memfd_test.c 
b/tools/testing/selftests/memfd/memfd_test.c
index 10baa1652fc2..4bd2b6c87bb4 100644
--- a/tools/testing/selftests/memfd/memfd_test.c
+++ b/tools/testing/selftests/memfd/memfd_test.c
@@ -27,7 +27,7 @@
 
 #define MFD_DEF_SIZE 8192
 #define STACK_SIZE 65536
-
+#define F_SEAL_FS_WRITE         0x0010
 /*
  * Default is not to test hugetlbfs
  */
@@ -170,6 +170,24 @@ static void *mfd_assert_mmap_shared(int fd)
        return p;
 }
 
+static void *mfd_fail_mmap_shared(int fd)
+{
+       void *p;
+
+       p = mmap(NULL,
+                mfd_def_size,
+                PROT_READ | PROT_WRITE,
+                MAP_SHARED,
+                fd,
+                0);
+       if (p != MAP_FAILED) {
+               printf("mmap() didn't fail as expected\n");
+               abort();
+       }
+
+       return p;
+}
+
 static void *mfd_assert_mmap_private(int fd)
 {
        void *p;
@@ -692,6 +710,36 @@ static void test_seal_write(void)
        close(fd);
 }
 
+/*
+ * Test SEAL_WRITE
+ * Test whether SEAL_WRITE actually prevents modifications.
+ */
+static void test_seal_fs_write(void)
+{
+       int fd;
+       void *p;
+
+       printf("%s SEAL-FS-WRITE\n", memfd_str);
+
+       fd = mfd_assert_new("kern_memfd_seal_fs_write",
+                           mfd_def_size,
+                           MFD_CLOEXEC | MFD_ALLOW_SEALING);
+
+       p = mfd_assert_mmap_shared(fd);
+
+       /* FS_WRITE seal can be added even with existing
+        * writeable mappings */
+       mfd_assert_has_seals(fd, 0);
+       mfd_assert_add_seals(fd, F_SEAL_FS_WRITE);
+       mfd_assert_has_seals(fd, F_SEAL_FS_WRITE);
+
+       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 +993,7 @@ int main(int argc, char **argv)
        test_basic();
 
        test_seal_write();
+       test_seal_fs_write();
        test_seal_shrink();
        test_seal_grow();
        test_seal_resize();
-- 
2.19.0.605.g01d371f741-goog