Re: [PATCH 3/4] selftests/memfd: add tests for F_SEAL_EXEC

[Jeff Xu]

Hi Shuah Khan

I will continue Daniel Verkamp's work on this patch.

Could you please take a look at the new patch set I sent to see if all
your comments are addressed ?

Much appreciated.

Best Regards,
Jeff.


On Thu, Jul 28, 2022 at 11:15 PM Jeff Xu <jeffxu@xxxxxxxxxx> wrote:
>
> From: Daniel Verkamp <dverkamp@xxxxxxxxxxxx>
>
> Basic tests to ensure that user/group/other execute bits cannot be
> changed after applying F_SEAL_EXEC to a memfd.
>
> Co-developed-by: Jeff Xu <jeffxu@xxxxxxxxxx>
> Signed-off-by: Jeff Xu <jeffxu@xxxxxxxxxx>
> Signed-off-by: Daniel Verkamp <dverkamp@xxxxxxxxxxxx>
> ---
>  tools/testing/selftests/memfd/memfd_test.c | 129 ++++++++++++++++++++-
>  1 file changed, 128 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c
> index 94df2692e6e4..1d7e7b36bbdd 100644
> --- a/tools/testing/selftests/memfd/memfd_test.c
> +++ b/tools/testing/selftests/memfd/memfd_test.c
> @@ -28,12 +28,44 @@
>  #define MFD_DEF_SIZE 8192
>  #define STACK_SIZE 65536
>
> +#ifndef F_SEAL_EXEC
> +#define F_SEAL_EXEC    0x0020
> +#endif
> +
> +#ifndef MAX_PATH
> +#define MAX_PATH 256
> +#endif
> +
>  /*
>   * 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[MAX_PATH];
> +       int size;
> +       ssize_t nbytes;
> +
> +       size = snprintf(buf1, MAX_PATH, "/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 +130,14 @@ static unsigned int mfd_assert_get_seals(int fd)
>
>  static void mfd_assert_has_seals(int fd, unsigned int seals)
>  {
> +       char buf[MAX_PATH];
> +       int nbytes;
>         unsigned int s;
> +       fd2name(fd, buf, MAX_PATH);
>
>         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 +629,64 @@ static void mfd_fail_grow_write(int fd)
>         }
>  }
>
> +static void mfd_assert_mode(int fd, int mode)
> +{
> +       struct stat st;
> +       char buf[MAX_PATH];
> +       int nbytes;
> +
> +       fd2name(fd, buf, MAX_PATH);
> +
> +       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[MAX_PATH];
> +       int nbytes;
> +
> +       fd2name(fd, buf, MAX_PATH);
> +
> +       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[MAX_PATH];
> +       int nbytes;
> +
> +       fd2name(fd, buf, MAX_PATH);
> +
> +       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 +973,39 @@ 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 +1185,7 @@ 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", "");
> --
> 2.37.1.455.g008518b4e5-goog
>