selftests/ovl: add third selftest for "override_creds"

Add a simple test to verify that the new "override_creds" option works.

Link: https://lore.kernel.org/r/20250219-work-overlayfs-v3-4-46af55e4ceda@kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

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 6b65e36105786446d9b0a75516c8fcadf8c9a6db..fd1e5d7c13a3481a08d94fb7e32c20956dd909d6 100644 (file)
--- 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 0e8080bd0aea57fa6badfac04e858a2763af179f..e553c89c5b19aea2bcec04f6b0ffe4571aeb0f9d 100644 (file)
--- a/tools/testing/selftests/filesystems/utils.c
+++ b/tools/testing/selftests/filesystems/utils.c
@@ -472,3 +472,30 @@ out:
        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 f35001a75f99d420b49d4e22002d47c42ca04343..7f1df2a3e94cfd6c78a3b38f3e92bb96ae2caca2 100644 (file)
--- 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);