[PATCH v4 2/2] selftests/memfd: Add tests for F_SEAL_FUTURE_WRITE seal

[Joel Fernandes]

From: "Joel Fernandes (Google)" <j...@joelfernandes.org>

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

Cc: dan...@google.com
Cc: minc...@kernel.org
Cc: Jann Horn <ja...@google.com>
Cc: John Stultz <john.stu...@linaro.org>
Signed-off-by: Joel Fernandes (Google) <j...@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..c67d32eeb668 100644
--- a/tools/testing/selftests/memfd/memfd_test.c
+++ b/tools/testing/selftests/memfd/memfd_test.c
@@ -54,6 +54,22 @@ static int mfd_assert_new(const char *name, loff_t sz, 
unsigned int flags)
        return fd;
 }
 
+static int mfd_assert_reopen_fd(int fd_in)
+{
+       int r, fd;
+       char path[100];
+
+       sprintf(path, "/proc/self/fd/%d", fd_in);
+
+       fd = open(path, O_RDWR);
+       if (fd < 0) {
+               printf("re-open of existing fd %d failed\n", fd_in);
+               abort();
+       }
+
+       return fd;
+}
+
 static void mfd_fail_new(const char *name, unsigned int flags)
 {
        int r;
@@ -255,6 +271,25 @@ static void mfd_assert_read(int fd)
        munmap(p, mfd_def_size);
 }
 
+/* Test that PROT_READ + MAP_SHARED mappings work. */
+static void mfd_assert_read_shared(int fd)
+{
+       void *p;
+
+       /* verify PROT_READ and MAP_SHARED *is* allowed */
+       p = mmap(NULL,
+                mfd_def_size,
+                PROT_READ,
+                MAP_SHARED,
+                fd,
+                0);
+       if (p == MAP_FAILED) {
+               printf("mmap() failed: %m\n");
+               abort();
+       }
+       munmap(p, mfd_def_size);
+}
+
 static void mfd_assert_write(int fd)
 {
        ssize_t l;
@@ -692,6 +727,44 @@ 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, fd2;
+       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);
+
+       mfd_assert_add_seals(fd, F_SEAL_FUTURE_WRITE);
+       mfd_assert_has_seals(fd, F_SEAL_FUTURE_WRITE);
+
+       /* read should pass, writes should fail */
+       mfd_assert_read(fd);
+       mfd_assert_read_shared(fd);
+       mfd_fail_write(fd);
+
+       fd2 = mfd_assert_reopen_fd(fd);
+       /* read should pass, writes should still fail */
+       mfd_assert_read(fd2);
+       mfd_assert_read_shared(fd2);
+       mfd_fail_write(fd2);
+
+       munmap(p, mfd_def_size);
+       close(fd2);
+       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();
-- 
2.20.1.97.g81188d93c3-goog