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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 unprivileged fchroot() into failfs is refused when the process is already chrooted: moving the root of a chrooted task into failfs would allow it to escape its chroot via openat(fd, "..") with a pre-opened directory fd, so the kernel refuses the syscall with EPERM. Signed-off-by: Andrea Cervesato --- runtest/staging | 1 + testcases/kernel/syscalls/fchroot/.gitignore | 1 + testcases/kernel/syscalls/fchroot/fchroot13.c | 63 +++++++++++++++++++++++++++ 3 files changed, 65 insertions(+) diff --git a/runtest/staging b/runtest/staging index 1655b6813..95e777ffb 100644 --- a/runtest/staging +++ b/runtest/staging @@ -12,3 +12,4 @@ fchroot09 fchroot09 fchroot10 fchroot10 fchroot11 fchroot11 fchroot12 fchroot12 +fchroot13 fchroot13 diff --git a/testcases/kernel/syscalls/fchroot/.gitignore b/testcases/kernel/syscalls/fchroot/.gitignore index de8ca0688..0c4461611 100644 --- a/testcases/kernel/syscalls/fchroot/.gitignore +++ b/testcases/kernel/syscalls/fchroot/.gitignore @@ -10,3 +10,4 @@ fchroot09 fchroot10 fchroot11 fchroot12 +fchroot13 diff --git a/testcases/kernel/syscalls/fchroot/fchroot13.c b/testcases/kernel/syscalls/fchroot/fchroot13.c new file mode 100644 index 000000000..e90e6f663 --- /dev/null +++ b/testcases/kernel/syscalls/fchroot/fchroot13.c @@ -0,0 +1,63 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Copyright (C) 2026 SUSE LLC Andrea Cervesato + */ + +/*\ + * Test that unprivileged :manpage:`fchroot(2)` into failfs is refused + * when the process is already chrooted. + * + * The root directory is what confines ".." resolution and the failfs root + * can never be reached by walking up a real mount tree. Moving the root + * of a chrooted task into failfs would allow it to escape its chroot via + * ``openat(fd, "..")`` with a pre-opened directory fd, so the kernel refuses + * the syscall with ``EPERM``. + * + * Root is required to create the chroot jail before dropping to an + * unprivileged user in the forked child. + */ + +#define _GNU_SOURCE +#include +#include +#include "tst_test.h" +#include "lapi/fcntl.h" +#include "lapi/prctl.h" +#include "lapi/syscalls.h" + +#define JAILDIR "jail" + +static struct passwd *ltpuser; + +static void run(void) +{ + if (SAFE_FORK()) + return; + + SAFE_CHROOT(JAILDIR); + SAFE_CHDIR("/"); + + SAFE_SETRESUID(ltpuser->pw_uid, ltpuser->pw_uid, + ltpuser->pw_uid); + + SAFE_PRCTL(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0); + + TST_EXP_FAIL(tst_syscall(__NR_fchroot, FD_FAILFS_ROOT, 0), + EPERM, "fchroot() from a chrooted process"); + + exit(0); +} + +static void setup(void) +{ + ltpuser = SAFE_GETPWNAM("nobody"); + SAFE_MKDIR(JAILDIR, 0755); +} + +static struct tst_test test = { + .setup = setup, + .test_all = run, + .needs_root = 1, + .needs_tmpdir = 1, + .forks_child = 1, +}; -- 2.51.0 -- Mailing list info: https://lists.linux.it/listinfo/ltp