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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: ltp-bounces+ltp=archiver.kernel.org@lists.linux.it Sender: "ltp" From: Andrea Cervesato Verify that entering failfs with fchroot() is hard to undo: a process inside counts as chrooted, so the remaining way out is a pre-opened mount namespace fd. setns() into it resets both the root and the working directory. Signed-off-by: Andrea Cervesato --- runtest/staging | 1 + testcases/kernel/syscalls/fchroot/.gitignore | 1 + testcases/kernel/syscalls/fchroot/fchroot09.c | 86 +++++++++++++++++++++++++++ 3 files changed, 88 insertions(+) diff --git a/runtest/staging b/runtest/staging index 8dfe95c4a..23f6c6a20 100644 --- a/runtest/staging +++ b/runtest/staging @@ -8,3 +8,4 @@ fchroot05 fchroot05 fchroot06 fchroot06 fchroot07 fchroot07 fchroot08 fchroot08 +fchroot09 fchroot09 diff --git a/testcases/kernel/syscalls/fchroot/.gitignore b/testcases/kernel/syscalls/fchroot/.gitignore index 0a2510d8a..b577da61f 100644 --- a/testcases/kernel/syscalls/fchroot/.gitignore +++ b/testcases/kernel/syscalls/fchroot/.gitignore @@ -7,3 +7,4 @@ fchroot06 fchroot07 fchroot07_child fchroot08 +fchroot09 diff --git a/testcases/kernel/syscalls/fchroot/fchroot09.c b/testcases/kernel/syscalls/fchroot/fchroot09.c new file mode 100644 index 000000000..a6bca5085 --- /dev/null +++ b/testcases/kernel/syscalls/fchroot/fchroot09.c @@ -0,0 +1,86 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Copyright (C) 2026 SUSE LLC Andrea Cervesato + */ + +/*\ + * Test that :manpage:`setns(2)` escapes the failfs root. + * + * Entering failfs with :manpage:`fchroot(2)` is hard to undo: a process + * inside counts as chrooted, so :manpage:`chroot(2)` and fchroot() back + * out require ``CAP_SYS_CHROOT``. The remaining way out is a pre-opened mount + * namespace file descriptor: setns() into it resets both the root and the + * working directory. + * + * Root is required because entering failfs requires ``CAP_SYS_CHROOT`` and + * :manpage:`setns(2)` into the mount namespace requires ``CAP_SYS_ADMIN``. + * + * The test runs in a forked child so the root of the parent process is + * left untouched. + */ + +#define _GNU_SOURCE +#include +#include +#include "tst_test.h" +#include "lapi/fcntl.h" +#include "lapi/sched.h" +#include "lapi/setns.h" +#include "lapi/syscalls.h" + +#define ABSDIR "abs" + +static void run(void) +{ + if (SAFE_FORK()) + return; + + struct stat realroot, st; + int nsfd; + + SAFE_STAT("/", &realroot); + nsfd = SAFE_OPEN("/proc/self/ns/mnt", O_RDONLY); + + TST_EXP_PASS(tst_syscall(__NR_fchroot, FD_FAILFS_ROOT, 0), + "fchroot() with the FD_FAILFS_ROOT sentinel"); + + TST_EXP_FAIL2(open(ABSDIR, O_PATH), EOPNOTSUPP, + "absolute lookup after entering failfs"); + + TST_EXP_PASS(setns(nsfd, CLONE_NEWNS), + "setns() back into the mount namespace"); + + SAFE_CLOSE(nsfd); + + SAFE_STAT("/", &st); + TST_EXP_EXPR(st.st_dev == realroot.st_dev && + st.st_ino == realroot.st_ino, + "root restored after setns()"); + + SAFE_STAT(".", &st); + TST_EXP_EXPR(st.st_dev == realroot.st_dev && + st.st_ino == realroot.st_ino, + "working directory restored after setns()"); + + exit(0); +} + +static void setup(void) +{ + char *tmpdir; + char abs_path[PATH_MAX]; + + tmpdir = tst_tmpdir_path(); + snprintf(abs_path, sizeof(abs_path), "%s/%s", tmpdir, "target"); + + SAFE_TOUCH("target", 0644, NULL); + SAFE_SYMLINK(abs_path, ABSDIR); +} + +static struct tst_test test = { + .test_all = run, + .setup = setup, + .needs_root = 1, + .forks_child = 1, + .needs_tmpdir = 1, +}; -- 2.51.0 -- Mailing list info: https://lists.linux.it/listinfo/ltp