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user_get_super() is now backed by the global device-to-superblock table instead of a walk of the super_blocks list. ustat(2) is its most direct user-visible consumer but nothing in the tree exercises it. Add a small regression test: the device number of a mounted tmpfs (an anonymous device, registered in the table by sget_fc()) must resolve, it must stop resolving after the unmount (the entry is dropped again in kill_super_notify()), and bogus device numbers keep reporting EINVAL. The test passes on kernels before the conversion: it pins down the semantics the table-backed lookup must preserve. Link: https://patch.msgid.link/20260616-work-super-bdev_holder_global-v2-18-7df6b864028e@kernel.org Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
136 lines
3.1 KiB
C
136 lines
3.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Test ustat(2): looking up superblocks by device number.
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*
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* ustat() resolves a device number to a mounted superblock via
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* user_get_super(). Check that the device number of a mounted tmpfs (an
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* anonymous device) resolves, that it stops resolving once the filesystem
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* is unmounted and that bogus device numbers report EINVAL.
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*/
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#define _GNU_SOURCE
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#include <errno.h>
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#include <fcntl.h>
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#include <sched.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/mount.h>
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#include <sys/stat.h>
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#include <sys/syscall.h>
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#include <unistd.h>
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#include "../kselftest_harness.h"
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/* struct ustat is not exported through UAPI, mirror include/linux/types.h. */
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struct ustat_buf {
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int f_tfree;
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unsigned long f_tinode;
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char f_fname[6];
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char f_fpack[6];
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/* slack in case an architecture lays the struct out differently */
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char pad[64];
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};
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#ifdef __NR_ustat
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/*
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* The kernel decodes @dev with new_decode_dev(), which matches the low 32
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* bits of the st_dev encoding stat(2) returns for any major below 4096.
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*/
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static int sys_ustat(unsigned int dev, struct ustat_buf *buf)
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{
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return syscall(__NR_ustat, dev, buf);
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}
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static int write_string(const char *path, const char *string)
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{
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ssize_t len = strlen(string);
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int fd;
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fd = open(path, O_WRONLY);
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if (fd < 0)
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return -1;
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if (write(fd, string, len) != len) {
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close(fd);
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return -1;
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}
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return close(fd);
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}
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/* Enter namespaces in which mounting a tmpfs instance is allowed. */
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static int setup_namespaces(void)
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{
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uid_t uid = getuid();
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gid_t gid = getgid();
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char map[64];
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if (unshare(CLONE_NEWNS | (uid ? CLONE_NEWUSER : 0)))
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return -1;
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if (uid) {
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if (write_string("/proc/self/setgroups", "deny"))
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return -1;
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snprintf(map, sizeof(map), "0 %d 1", uid);
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if (write_string("/proc/self/uid_map", map))
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return -1;
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snprintf(map, sizeof(map), "0 %d 1", gid);
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if (write_string("/proc/self/gid_map", map))
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return -1;
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}
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return mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, NULL);
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}
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TEST(resolves_mounted_superblock)
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{
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char dir[] = "/tmp/ustat_test.XXXXXX";
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struct ustat_buf ub;
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struct stat st;
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ASSERT_NE(NULL, mkdtemp(dir));
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if (setup_namespaces()) {
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rmdir(dir);
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SKIP(return, "cannot set up namespaces: %s", strerror(errno));
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}
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ASSERT_EQ(0, mount("ustat_test", dir, "tmpfs", 0, NULL));
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ASSERT_EQ(0, stat(dir, &st));
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memset(&ub, 0xff, sizeof(ub));
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ASSERT_EQ(0, sys_ustat(st.st_dev, &ub))
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TH_LOG("ustat(%u): %s", (unsigned int)st.st_dev,
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strerror(errno));
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ASSERT_EQ(0, umount(dir));
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/* The unmount removed the superblock, the device is gone. */
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ASSERT_EQ(-1, sys_ustat(st.st_dev, &ub));
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ASSERT_EQ(EINVAL, errno);
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rmdir(dir);
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}
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TEST(bogus_device_numbers)
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{
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struct ustat_buf ub;
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ASSERT_EQ(-1, sys_ustat(0, &ub));
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ASSERT_EQ(EINVAL, errno);
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/* major 4095, minor 1048575: nothing plausible lives there */
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ASSERT_EQ(-1, sys_ustat((0xfffu << 8) | 0xffu | (0xfff00u << 12), &ub));
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ASSERT_EQ(EINVAL, errno);
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}
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#else /* !__NR_ustat */
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TEST(unsupported)
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{
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SKIP(return, "ustat(2) is not available on this architecture");
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}
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#endif /* __NR_ustat */
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TEST_HARNESS_MAIN
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