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Subject[PATCH v8 2/5] selftests/memfd: add tests for F_SEAL_EXEC
Date
From: Daniel Verkamp <dverkamp@chromium.org>

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@chromium.org>
Co-developed-by: Jeff Xu <jeffxu@google.com>
Signed-off-by: Jeff Xu <jeffxu@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
tools/testing/selftests/memfd/memfd_test.c | 123 ++++++++++++++++++++-
1 file changed, 122 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c
index 94df2692e6e4..f18a15a1f275 100644
--- a/tools/testing/selftests/memfd/memfd_test.c
+++ b/tools/testing/selftests/memfd/memfd_test.c
@@ -28,12 +28,38 @@
#define MFD_DEF_SIZE 8192
#define STACK_SIZE 65536

+#define F_SEAL_EXEC 0x0020
+
/*
* Default is not to test hugetlbfs
*/
static size_t mfd_def_size = MFD_DEF_SIZE;
static const char *memfd_str = MEMFD_STR;

+static ssize_t fd2name(int fd, char *buf, size_t bufsize)
+{
+ char buf1[PATH_MAX];
+ int size;
+ ssize_t nbytes;
+
+ size = snprintf(buf1, PATH_MAX, "/proc/self/fd/%d", fd);
+ if (size < 0) {
+ printf("snprintf(%d) failed on %m\n", fd);
+ abort();
+ }
+
+ /*
+ * reserver one byte for string termination.
+ */
+ nbytes = readlink(buf1, buf, bufsize-1);
+ if (nbytes == -1) {
+ printf("readlink(%s) failed %m\n", buf1);
+ abort();
+ }
+ buf[nbytes] = '\0';
+ return nbytes;
+}
+
static int mfd_assert_new(const char *name, loff_t sz, unsigned int flags)
{
int r, fd;
@@ -98,11 +124,14 @@ static unsigned int mfd_assert_get_seals(int fd)

static void mfd_assert_has_seals(int fd, unsigned int seals)
{
+ char buf[PATH_MAX];
+ int nbytes;
unsigned int s;
+ fd2name(fd, buf, PATH_MAX);

s = mfd_assert_get_seals(fd);
if (s != seals) {
- printf("%u != %u = GET_SEALS(%d)\n", seals, s, fd);
+ printf("%u != %u = GET_SEALS(%s)\n", seals, s, buf);
abort();
}
}
@@ -594,6 +623,64 @@ static void mfd_fail_grow_write(int fd)
}
}

+static void mfd_assert_mode(int fd, int mode)
+{
+ struct stat st;
+ char buf[PATH_MAX];
+ int nbytes;
+
+ fd2name(fd, buf, PATH_MAX);
+
+ if (fstat(fd, &st) < 0) {
+ printf("fstat(%s) failed: %m\n", buf);
+ abort();
+ }
+
+ if ((st.st_mode & 07777) != mode) {
+ printf("fstat(%s) wrong file mode 0%04o, but expected 0%04o\n",
+ buf, (int)st.st_mode & 07777, mode);
+ abort();
+ }
+}
+
+static void mfd_assert_chmod(int fd, int mode)
+{
+ char buf[PATH_MAX];
+ int nbytes;
+
+ fd2name(fd, buf, PATH_MAX);
+
+ if (fchmod(fd, mode) < 0) {
+ printf("fchmod(%s, 0%04o) failed: %m\n", buf, mode);
+ abort();
+ }
+
+ mfd_assert_mode(fd, mode);
+}
+
+static void mfd_fail_chmod(int fd, int mode)
+{
+ struct stat st;
+ char buf[PATH_MAX];
+ int nbytes;
+
+ fd2name(fd, buf, PATH_MAX);
+
+ if (fstat(fd, &st) < 0) {
+ printf("fstat(%s) failed: %m\n", buf);
+ abort();
+ }
+
+ if (fchmod(fd, mode) == 0) {
+ printf("fchmod(%s, 0%04o) didn't fail as expected\n",
+ buf, mode);
+ 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 +967,39 @@ 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 +1179,7 @@ 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", "");
--
2.39.0.rc1.256.g54fd8350bd-goog
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