On Wed, Feb 19, 2025 at 11:02 AM Christian Brauner <brauner@xxxxxxxxxx> wrote:
>
> Add a simple test to verify that the new "override_creds" option works.
>
> Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
> .../filesystems/overlayfs/set_layers_via_fds.c | 80 ++++++++++++++++++++++
> tools/testing/selftests/filesystems/utils.c | 27 ++++++++
> tools/testing/selftests/filesystems/utils.h | 1 +
> 3 files changed, 108 insertions(+)
>
> diff --git a/tools/testing/selftests/filesystems/overlayfs/set_layers_via_fds.c b/tools/testing/selftests/filesystems/overlayfs/set_layers_via_fds.c
> index 6b65e3610578..fd1e5d7c13a3 100644
> --- a/tools/testing/selftests/filesystems/overlayfs/set_layers_via_fds.c
> +++ b/tools/testing/selftests/filesystems/overlayfs/set_layers_via_fds.c
> @@ -8,6 +8,7 @@
> #include <string.h>
> #include <sys/socket.h>
> #include <sys/stat.h>
> +#include <sys/sysmacros.h>
> #include <sys/mount.h>
> #include <unistd.h>
>
> @@ -442,4 +443,83 @@ TEST_F(set_layers_via_fds, set_override_creds_invalid)
> ASSERT_EQ(close(fd_userns2), 0);
> }
>
> +TEST_F(set_layers_via_fds, set_override_creds_nomknod)
> +{
> + int fd_context, fd_tmpfs, fd_overlay;
> + int layer_fds[] = { [0 ... 3] = -EBADF };
> + pid_t pid;
> + int pidfd;
> +
> + ASSERT_EQ(unshare(CLONE_NEWNS), 0);
> + ASSERT_EQ(sys_mount(NULL, "/", NULL, MS_SLAVE | MS_REC, NULL), 0);
> +
> + fd_context = sys_fsopen("tmpfs", 0);
> + ASSERT_GE(fd_context, 0);
> +
> + ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_CMD_CREATE, NULL, NULL, 0), 0);
> + fd_tmpfs = sys_fsmount(fd_context, 0, 0);
> + ASSERT_GE(fd_tmpfs, 0);
> + ASSERT_EQ(close(fd_context), 0);
> +
> + ASSERT_EQ(mkdirat(fd_tmpfs, "w", 0755), 0);
> + ASSERT_EQ(mkdirat(fd_tmpfs, "u", 0755), 0);
> + ASSERT_EQ(mkdirat(fd_tmpfs, "l1", 0755), 0);
> + ASSERT_EQ(mkdirat(fd_tmpfs, "l2", 0755), 0);
> +
> + layer_fds[0] = openat(fd_tmpfs, "w", O_DIRECTORY);
> + ASSERT_GE(layer_fds[0], 0);
> +
> + layer_fds[1] = openat(fd_tmpfs, "u", O_DIRECTORY);
> + ASSERT_GE(layer_fds[1], 0);
> +
> + layer_fds[2] = openat(fd_tmpfs, "l1", O_DIRECTORY);
> + ASSERT_GE(layer_fds[2], 0);
> +
> + layer_fds[3] = openat(fd_tmpfs, "l2", O_DIRECTORY);
> + ASSERT_GE(layer_fds[3], 0);
> +
> + ASSERT_EQ(sys_move_mount(fd_tmpfs, "", -EBADF, "/tmp", MOVE_MOUNT_F_EMPTY_PATH), 0);
> + ASSERT_EQ(close(fd_tmpfs), 0);
> +
> + fd_context = sys_fsopen("overlay", 0);
> + ASSERT_GE(fd_context, 0);
> +
> + ASSERT_NE(sys_fsconfig(fd_context, FSCONFIG_SET_FD, "lowerdir", NULL, layer_fds[2]), 0);
> +
> + ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_SET_FD, "workdir", NULL, layer_fds[0]), 0);
> + ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_SET_FD, "upperdir", NULL, layer_fds[1]), 0);
> + ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_SET_FD, "lowerdir+", NULL, layer_fds[2]), 0);
> + ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_SET_FD, "lowerdir+", NULL, layer_fds[3]), 0);
> + ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_SET_FLAG, "userxattr", NULL, 0), 0);
> +
> + pid = create_child(&pidfd, 0);
> + ASSERT_GE(pid, 0);
> + if (pid == 0) {
> + if (!cap_down(CAP_MKNOD))
> + _exit(EXIT_FAILURE);
> +
> + if (!cap_down(CAP_SYS_ADMIN))
> + _exit(EXIT_FAILURE);
> +
> + if (sys_fsconfig(fd_context, FSCONFIG_SET_FLAG, "override_creds", NULL, 0))
> + _exit(EXIT_FAILURE);
> +
> + _exit(EXIT_SUCCESS);
> + }
> + ASSERT_EQ(sys_waitid(P_PID, pid, NULL, WEXITED), 0);
> + ASSERT_GE(close(pidfd), 0);
> +
> + ASSERT_EQ(sys_fsconfig(fd_context, FSCONFIG_CMD_CREATE, NULL, NULL, 0), 0);
> +
> + fd_overlay = sys_fsmount(fd_context, 0, 0);
> + ASSERT_GE(fd_overlay, 0);
> +
> + ASSERT_EQ(sys_move_mount(fd_overlay, "", -EBADF, "/set_layers_via_fds", MOVE_MOUNT_F_EMPTY_PATH), 0);
> + ASSERT_EQ(mknodat(fd_overlay, "dev-zero", S_IFCHR | 0644, makedev(1, 5)), -1);
> + ASSERT_EQ(errno, EPERM);
> +
> + ASSERT_EQ(close(fd_context), 0);
> + ASSERT_EQ(close(fd_overlay), 0);
> +}
> +
> TEST_HARNESS_MAIN
> diff --git a/tools/testing/selftests/filesystems/utils.c b/tools/testing/selftests/filesystems/utils.c
> index 0e8080bd0aea..e553c89c5b19 100644
> --- a/tools/testing/selftests/filesystems/utils.c
> +++ b/tools/testing/selftests/filesystems/utils.c
> @@ -472,3 +472,30 @@ int caps_down(void)
> cap_free(caps);
> return fret;
> }
> +
> +/* cap_down - lower an effective cap */
> +int cap_down(cap_value_t down)
> +{
> + bool fret = false;
> + cap_t caps = NULL;
> + cap_value_t cap = down;
> + int ret = -1;
> +
> + caps = cap_get_proc();
> + if (!caps)
> + goto out;
> +
> + ret = cap_set_flag(caps, CAP_EFFECTIVE, 1, &cap, 0);
> + if (ret)
> + goto out;
> +
> + ret = cap_set_proc(caps);
> + if (ret)
> + goto out;
> +
> + fret = true;
> +
> +out:
> + cap_free(caps);
> + return fret;
> +}
> diff --git a/tools/testing/selftests/filesystems/utils.h b/tools/testing/selftests/filesystems/utils.h
> index f35001a75f99..7f1df2a3e94c 100644
> --- a/tools/testing/selftests/filesystems/utils.h
> +++ b/tools/testing/selftests/filesystems/utils.h
> @@ -24,6 +24,7 @@ extern int get_userns_fd(unsigned long nsid, unsigned long hostid,
> unsigned long range);
>
> extern int caps_down(void);
> +extern int cap_down(cap_value_t down);
>
> extern bool switch_ids(uid_t uid, gid_t gid);
>
>
> --
> 2.47.2
>
