sysctl: move umh sysctl registration to its own file

Move the umh sysctl registration to its own file, the array is
already there. We do this to remove the clutter out of kernel/sysctl.c
to avoid merge conflicts.

This also lets the sysctls not be built at all now when CONFIG_SYSCTL
is not enabled.

This has a small penalty of 23 bytes but soon we'll be removing
all the empty entries on sysctl arrays so just do this cleanup
now:

./scripts/bloat-o-meter vmlinux.base vmlinux.1
add/remove: 2/0 grow/shrink: 0/1 up/down: 49/-26 (23)
Function old new delta
init_umh_sysctls - 33 +33
__pfx_init_umh_sysctls - 16 +16
sysctl_init_bases 111 85 -26
Total: Before=21256914, After=21256937, chg +0.00%

Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

freezer,umh: Clean up freezer/initrd interaction

handle_initrd() marks itself as PF_FREEZER_SKIP in order to ensure
that the UMH, which is going to freeze the system, doesn't
indefinitely wait for it's caller.

Rework things by adding UMH_FREEZABLE to indicate the completion is
freezable.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20220822114648.791019324@infradead.org

umh: Stop calling do_execve_file

With the user mode driver code changed to not set subprocess_info.file
there are no more users of subproces_info.file. Remove this field
from struct subprocess_info and remove the only user in
call_usermodehelper_exec_async that would call do_execve_file instead
of do_execve if file was set.

v1: https://lkml.kernel.org/r/877dvuf0i7.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87r1tx4p2a.fsf_-_@x220.int.ebiederm.org
Link: https://lkml.kernel.org/r/20200702164140.4468-9-ebiederm@xmission.com
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

umh: Separate the user mode driver and the user mode helper support

This makes it clear which code is part of the core user mode
helper support and which code is needed to implement user mode
drivers.

This makes the kernel smaller for everyone who does not use a usermode
driver.

v1: https://lkml.kernel.org/r/87tuyyf0ln.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87imf963s6.fsf_-_@x220.int.ebiederm.org
Link: https://lkml.kernel.org/r/20200702164140.4468-5-ebiederm@xmission.com
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

umh: Remove call_usermodehelper_setup_file.

The only caller of call_usermodehelper_setup_file is fork_usermode_blob.
In fork_usermode_blob replace call_usermodehelper_setup_file with
call_usermodehelper_setup and delete fork_usermodehelper_setup_file.

For this to work the argv_free is moved from umh_clean_and_save_pid
to fork_usermode_blob.

v1: https://lkml.kernel.org/r/87zh8qf0mp.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87o8p163u1.fsf_-_@x220.int.ebiederm.org
Link: https://lkml.kernel.org/r/20200702164140.4468-4-ebiederm@xmission.com
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

umh: Capture the pid in umh_pipe_setup

The pid in struct subprocess_info is only used by umh_clean_and_save_pid to
write the pid into umh_info.

Instead always capture the pid on struct umh_info in umh_pipe_setup, removing
code that is specific to user mode drivers from the common user path of
user mode helpers.

v1: https://lkml.kernel.org/r/87h7uygf9i.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/875zb97iix.fsf_-_@x220.int.ebiederm.org
Link: https://lkml.kernel.org/r/20200702164140.4468-1-ebiederm@xmission.com
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

umh: add exit routine for UMH process

A UMH process which is created by the fork_usermode_blob() such as
bpfilter needs to release members of the umh_info when process is
terminated.
But the do_exit() does not release members of the umh_info. hence module
which uses UMH needs own code to detect whether UMH process is
terminated or not.
But this implementation needs extra code for checking the status of
UMH process. it eventually makes the code more complex.

The new PF_UMH flag is added and it is used to identify UMH processes.
The exit_umh() does not release members of the umh_info.
Hence umh_info->cleanup callback should release both members of the
umh_info and the private data.

Suggested-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

umh: Add command line to user mode helpers

User mode helpers were spawned without a command line, and because
an empty command line is used by many tools to identify processes as
kernel threads, this could cause some issues.

Notably during killing spree on shutdown, since such helper would then
be skipped (i.e. not killed) which would result in the process remaining
alive, and thus preventing unmouting of the rootfs (as experienced with
the bpfilter umh).

Fixes: 449325b52b7a ("umh: introduce fork_usermode_blob() helper")
Signed-off-by: Olivier Brunel <jjk@jjacky.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

umh: introduce fork_usermode_blob() helper

Introduce helper:
int fork_usermode_blob(void *data, size_t len, struct umh_info *info);
struct umh_info {
struct file *pipe_to_umh;
struct file *pipe_from_umh;
pid_t pid;
};

that GPLed kernel modules (signed or unsigned) can use it to execute part
of its own data as swappable user mode process.

The kernel will do:
- allocate a unique file in tmpfs
- populate that file with [data, data + len] bytes
- user-mode-helper code will do_execve that file and, before the process
starts, the kernel will create two unix pipes for bidirectional
communication between kernel module and umh
- close tmpfs file, effectively deleting it
- the fork_usermode_blob will return zero on success and populate
'struct umh_info' with two unix pipes and the pid of the user process

As the first step in the development of the bpfilter project
the fork_usermode_blob() helper is introduced to allow user mode code
to be invoked from a kernel module. The idea is that user mode code plus
normal kernel module code are built as part of the kernel build
and installed as traditional kernel module into distro specified location,
such that from a distribution point of view, there is
no difference between regular kernel modules and kernel modules + umh code.
Such modules can be signed, modprobed, rmmod, etc. The use of this new helper
by a kernel module doesn't make it any special from kernel and user space
tooling point of view.

Such approach enables kernel to delegate functionality traditionally done
by the kernel modules into the user space processes (either root or !root) and
reduces security attack surface of the new code. The buggy umh code would crash
the user process, but not the kernel. Another advantage is that umh code
of the kernel module can be debugged and tested out of user space
(e.g. opening the possibility to run clang sanitizers, fuzzers or
user space test suites on the umh code).
In case of the bpfilter project such architecture allows complex control plane
to be done in the user space while bpf based data plane stays in the kernel.

Since umh can crash, can be oom-ed by the kernel, killed by the admin,
the kernel module that uses them (like bpfilter) needs to manage life
time of umh on its own via two unix pipes and the pid of umh.

The exit code of such kernel module should kill the umh it started,
so that rmmod of the kernel module will cleanup the corresponding umh.
Just like if the kernel module does kmalloc() it should kfree() it
in the exit code.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

kmod: split off umh headers into its own file

In the future usermode helper users do not need to carry in all the of
kmod headers declarations.

Since kmod.h still includes umh.h this change has no functional changes,
each umh user can be cleaned up separately later and with time.

Link: http://lkml.kernel.org/r/20170810180618.22457-4-mcgrof@kernel.org
Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Jessica Yu <jeyu@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Michal Marek <mmarek@suse.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Matt Redfearn <matt.redfearn@imgtec.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Colin Ian King <colin.king@canonical.com>
Cc: Daniel Mentz <danielmentz@google.com>
Cc: David Binderman <dcb314@hotmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>