--- /dev/null
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <sched.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/fsuid.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+
+#include <linux/mount.h>
+#include <linux/types.h>
+
+#include "kselftest_harness.h"
+#include "wrappers.h"
+#include "utils.h"
+
+/*
+ * The test mount maps caller-visible ids [0, MAP_RANGE) onto the on-disk range
+ * [MAP_HOST, MAP_HOST + MAP_RANGE). An id outside [0, MAP_RANGE) therefore has
+ * no mapping in the mount and is not representable in the filesystem.
+ */
+#define MAP_HOST 10000
+#define MAP_RANGE 10000
+#define UNMAPPED 50000
+
+#ifndef MOUNT_ATTR_IDMAP
+#define MOUNT_ATTR_IDMAP 0x00100000
+#endif
+
+#ifndef __NR_mount_setattr
+#define __NR_mount_setattr 442
+#endif
+
+static inline int sys_mount_setattr(int dfd, const char *path,
+ unsigned int flags,
+ struct mount_attr *attr, size_t size)
+{
+ return syscall(__NR_mount_setattr, dfd, path, flags, attr, size);
+}
+
+/*
+ * Clone @path into a detached mount idmapped so that caller-visible ids
+ * [0, MAP_RANGE) map onto the on-disk ids [MAP_HOST, MAP_HOST + MAP_RANGE).
+ * Returns the mount fd, or -1 if idmapped mounts are not available.
+ */
+static int idmapped_clone(const char *path)
+{
+ struct mount_attr attr = {
+ .attr_set = MOUNT_ATTR_IDMAP,
+ };
+ int fd_tree, userns_fd, ret;
+
+ fd_tree = sys_open_tree(AT_FDCWD, path,
+ OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC);
+ if (fd_tree < 0)
+ return -1;
+
+ userns_fd = get_userns_fd(MAP_HOST, 0, MAP_RANGE);
+ if (userns_fd < 0) {
+ close(fd_tree);
+ return -1;
+ }
+
+ attr.userns_fd = userns_fd;
+ ret = sys_mount_setattr(fd_tree, "", AT_EMPTY_PATH, &attr, sizeof(attr));
+ close(userns_fd);
+ if (ret) {
+ close(fd_tree);
+ return -1;
+ }
+
+ return fd_tree;
+}
+
+FIXTURE(idmapped_tmpfile) {
+ char dir[64]; /* non-idmapped path to the layer directory */
+};
+
+FIXTURE_SETUP(idmapped_tmpfile)
+{
+ /* Private mount namespace so test mounts need no cleanup. */
+ ASSERT_EQ(unshare(CLONE_NEWNS), 0);
+ ASSERT_EQ(sys_mount(NULL, "/", NULL, MS_SLAVE | MS_REC, NULL), 0);
+ ASSERT_EQ(sys_mount("tmpfs", "/tmp", "tmpfs", 0, NULL), 0);
+
+ snprintf(self->dir, sizeof(self->dir), "/tmp/d");
+ ASSERT_EQ(mkdir(self->dir, 0777), 0);
+ /* World-writable so an unmapped caller still passes permission(). */
+ ASSERT_EQ(chmod(self->dir, 0777), 0);
+}
+
+FIXTURE_TEARDOWN(idmapped_tmpfile)
+{
+}
+
+/*
+ * A caller whose fsuid/fsgid have no mapping in the idmapped mount must not be
+ * able to create an O_TMPFILE. Without the check in vfs_tmpfile() the inode
+ * would be created owned by (uid_t)-1 and could then be linked into the
+ * namespace.
+ */
+TEST_F(idmapped_tmpfile, unmapped_caller_is_refused)
+{
+ int mfd, fd;
+
+ mfd = idmapped_clone(self->dir);
+ if (mfd < 0)
+ SKIP(return, "idmapped mounts not supported");
+
+ /* Become a caller outside the mount's [0, MAP_RANGE) range. */
+ setfsgid(UNMAPPED);
+ setfsuid(UNMAPPED);
+ ASSERT_EQ(setfsuid(-1), UNMAPPED);
+
+ fd = openat(mfd, ".", O_TMPFILE | O_WRONLY, 0644);
+ ASSERT_LT(fd, 0);
+ EXPECT_EQ(errno, EOVERFLOW);
+ if (fd >= 0)
+ close(fd);
+
+ EXPECT_EQ(close(mfd), 0);
+}
+
+/*
+ * A mapped caller can create an O_TMPFILE and link it into the namespace; the
+ * ownership round-trips through the mount idmap. This is what makes refusing
+ * the unmapped case above necessary in the first place.
+ */
+TEST_F(idmapped_tmpfile, mapped_caller_creates_and_links)
+{
+ char path[PATH_MAX];
+ struct stat st;
+ int mfd, fd;
+
+ mfd = idmapped_clone(self->dir);
+ if (mfd < 0)
+ SKIP(return, "idmapped mounts not supported");
+
+ /* Caller is uid/gid 0, which maps to MAP_HOST through the mount. */
+ fd = openat(mfd, ".", O_TMPFILE | O_RDWR, 0600);
+ ASSERT_GE(fd, 0);
+
+ ASSERT_EQ(fstat(fd, &st), 0);
+ EXPECT_EQ(st.st_uid, 0);
+ EXPECT_EQ(st.st_gid, 0);
+
+ /* The tmpfile is linkable: splice it into the directory. */
+ ASSERT_EQ(linkat(fd, "", mfd, "linked", AT_EMPTY_PATH), 0);
+ EXPECT_EQ(close(fd), 0);
+
+ ASSERT_EQ(fstatat(mfd, "linked", &st, 0), 0);
+ EXPECT_EQ(st.st_uid, 0);
+ EXPECT_EQ(st.st_gid, 0);
+
+ /* On the underlying, non-idmapped tmpfs it is stored as MAP_HOST. */
+ snprintf(path, sizeof(path), "%s/linked", self->dir);
+ ASSERT_EQ(stat(path, &st), 0);
+ EXPECT_EQ(st.st_uid, MAP_HOST);
+ EXPECT_EQ(st.st_gid, MAP_HOST);
+
+ EXPECT_EQ(close(mfd), 0);
+}
+
+TEST_HARNESS_MAIN
projects / thirdparty / linux.git / commitdiff
