[PATCH 2/2] selftests/memfd: add F_SEAL_PUNCH_HOLE tests

[Samiullah Khawaja <skhawaja@google.com>]

Add tests for the new F_SEAL_PUNCH_HOLE seal. Like the rest of
memfd_test, they run on shmem memfds by default and on hugetlbfs memfds
when memfd_test is invoked with the "hugetlbfs" argument.

mfd_assert_write() checks that the file can be written, and then also
checks that a hole can be punched into it. The second check no longer
holds once F_SEAL_PUNCH_HOLE is set. Move the write checks into
__mfd_assert_write() and the punch check into mfd_assert_punch_hole(),
and have mfd_assert_write() call both, so the existing tests keep doing
exactly what they did before.

Add mfd_fail_punch_hole(), which checks that both
fallocate(FALLOC_FL_PUNCH_HOLE) and madvise(MADV_REMOVE) fail with
EPERM, and use it in two new tests. SEAL-PUNCH-HOLE sets only the new
seal and checks that punching a hole fails, while writing, shrinking and
growing the file still work. SEAL-PUNCH-HOLE-SHRINK adds F_SEAL_SHRINK
as well and checks that the file can neither have holes punched into it
nor be shrunk, while it can still grow.

Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
---
 tools/testing/selftests/memfd/memfd_test.c | 111 ++++++++++++++++++++-
 1 file changed, 110 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c
index cdab3a837624..095c5eb255af 100644
--- a/tools/testing/selftests/memfd/memfd_test.c
+++ b/tools/testing/selftests/memfd/memfd_test.c
@@ -35,6 +35,10 @@
 
 #define F_SEAL_EXEC	0x0020
 
+#ifndef F_SEAL_PUNCH_HOLE
+#define F_SEAL_PUNCH_HOLE	0x0040
+#endif
+
 #define F_WX_SEALS (F_SEAL_SHRINK | \
 		    F_SEAL_GROW | \
 		    F_SEAL_WRITE | \
@@ -455,7 +459,7 @@ static void mfd_assert_fork_private_write(int fd)
 	munmap(p, mfd_def_size);
 }
 
-static void mfd_assert_write(int fd)
+static void __mfd_assert_write(int fd)
 {
 	ssize_t l;
 	void *p;
@@ -523,6 +527,11 @@ static void mfd_assert_write(int fd)
 
 	*(char *)p = 0;
 	munmap(p, mfd_def_size);
+}
+
+static void mfd_assert_punch_hole(int fd)
+{
+	int r;
 
 	/* verify PUNCH_HOLE works */
 	r = fallocate(fd,
@@ -535,6 +544,49 @@ static void mfd_assert_write(int fd)
 	}
 }
 
+static void mfd_fail_punch_hole(int fd)
+{
+	void *p;
+	int r;
+
+	/* verify PUNCH_HOLE fails */
+	r = fallocate(fd,
+		      FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+		      0,
+		      mfd_def_size);
+	if (r >= 0 || errno != EPERM) {
+		printf("expected EPERM on fallocate(PUNCH_HOLE), but got %d: %m\n",
+		       r);
+		abort();
+	}
+
+	/* verify MADV_REMOVE fails, it punches a hole as well */
+	p = mmap(NULL,
+		 mfd_def_size,
+		 PROT_READ | PROT_WRITE,
+		 MAP_SHARED,
+		 fd,
+		 0);
+	if (p == MAP_FAILED) {
+		printf("mmap() failed: %m\n");
+		abort();
+	}
+
+	r = madvise(p, mfd_def_size, MADV_REMOVE);
+	if (r >= 0 || errno != EPERM) {
+		printf("expected EPERM on madvise(MADV_REMOVE), but got %d: %m\n",
+		       r);
+		abort();
+	}
+	munmap(p, mfd_def_size);
+}
+
+static void mfd_assert_write(int fd)
+{
+	__mfd_assert_write(fd);
+	mfd_assert_punch_hole(fd);
+}
+
 static void mfd_fail_write(int fd)
 {
 	ssize_t l;
@@ -1117,6 +1169,61 @@ static void test_seal_resize(void)
 	close(fd);
 }
 
+/*
+ * Test SEAL_PUNCH_HOLE
+ * Test whether SEAL_PUNCH_HOLE actually prevents punching holes, but still
+ * allows writing and resizing
+ */
+static void test_seal_punch_hole(void)
+{
+	int fd;
+
+	printf("%s SEAL-PUNCH-HOLE\n", memfd_str);
+
+	fd = mfd_assert_new("kern_memfd_seal_punch_hole",
+			    mfd_def_size,
+			    MFD_CLOEXEC | MFD_ALLOW_SEALING);
+	mfd_assert_has_seals(fd, 0);
+	mfd_assert_add_seals(fd, F_SEAL_PUNCH_HOLE);
+	mfd_assert_has_seals(fd, F_SEAL_PUNCH_HOLE);
+
+	mfd_assert_read(fd);
+	__mfd_assert_write(fd);
+	mfd_fail_punch_hole(fd);
+	mfd_assert_shrink(fd);
+	mfd_assert_grow(fd);
+	mfd_assert_grow_write(fd);
+
+	close(fd);
+}
+
+/*
+ * Test SEAL_PUNCH_HOLE | SEAL_SHRINK
+ * Test whether SEAL_PUNCH_HOLE | SEAL_SHRINK prevents removing pages from
+ * the file
+ */
+static void test_seal_punch_hole_shrink(void)
+{
+	int fd;
+
+	printf("%s SEAL-PUNCH-HOLE-SHRINK\n", memfd_str);
+
+	fd = mfd_assert_new("kern_memfd_seal_punch_hole_shrink",
+			    mfd_def_size,
+			    MFD_CLOEXEC | MFD_ALLOW_SEALING);
+	mfd_assert_has_seals(fd, 0);
+	mfd_assert_add_seals(fd, F_SEAL_PUNCH_HOLE | F_SEAL_SHRINK);
+	mfd_assert_has_seals(fd, F_SEAL_PUNCH_HOLE | F_SEAL_SHRINK);
+
+	mfd_assert_read(fd);
+	__mfd_assert_write(fd);
+	mfd_fail_punch_hole(fd);
+	mfd_fail_shrink(fd);
+	mfd_assert_grow(fd);
+
+	close(fd);
+}
+
 /*
  * Test SEAL_EXEC
  * Test fd is created with exec and allow sealing.
@@ -1736,6 +1843,8 @@ int main(int argc, char **argv)
 	test_seal_shrink();
 	test_seal_grow();
 	test_seal_resize();
+	test_seal_punch_hole();
+	test_seal_punch_hole_shrink();
 
 	if (pid_ns_supported()) {
 		test_sysctl_simple();
-- 
2.56.0.307.g5fe7bd680c-goog