selftests/memfd: add tests for F_SEAL_EXEC

Basic tests to ensure that user/group/other execute bits cannot be changed
after applying F_SEAL_EXEC to a memfd.

Link: https://lkml.kernel.org/r/20221215001205.51969-3-jeffxu@google.com
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>
Cc: David Herrmann <dh.herrmann@gmail.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jorge Lucangeli Obes <jorgelo@chromium.org>
Cc: kernel test robot <lkp@intel.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c
index 94df269..f18a15a 100644 (file)
--- 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", "");