blob_to_mnt(): kern_unmount() is needed to undo kern_mount()

plain mntput() won't do.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

switch file_open_root() to struct path

... and provide file_open_root_mnt(), using the root of given mount.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

bpf: Fix umd memory leak in copy_process()

The syzbot reported a memleak as follows:

BUG: memory leak
unreferenced object 0xffff888101b41d00 (size 120):
comm "kworker/u4:0", pid 8, jiffies 4294944270 (age 12.780s)
backtrace:
[<ffffffff8125dc56>] alloc_pid+0x66/0x560
[<ffffffff81226405>] copy_process+0x1465/0x25e0
[<ffffffff81227943>] kernel_clone+0xf3/0x670
[<ffffffff812281a1>] kernel_thread+0x61/0x80
[<ffffffff81253464>] call_usermodehelper_exec_work
[<ffffffff81253464>] call_usermodehelper_exec_work+0xc4/0x120
[<ffffffff812591c9>] process_one_work+0x2c9/0x600
[<ffffffff81259ab9>] worker_thread+0x59/0x5d0
[<ffffffff812611c8>] kthread+0x178/0x1b0
[<ffffffff8100227f>] ret_from_fork+0x1f/0x30

unreferenced object 0xffff888110ef5c00 (size 232):
comm "kworker/u4:0", pid 8414, jiffies 4294944270 (age 12.780s)
backtrace:
[<ffffffff8154a0cf>] kmem_cache_zalloc
[<ffffffff8154a0cf>] __alloc_file+0x1f/0xf0
[<ffffffff8154a809>] alloc_empty_file+0x69/0x120
[<ffffffff8154a8f3>] alloc_file+0x33/0x1b0
[<ffffffff8154ab22>] alloc_file_pseudo+0xb2/0x140
[<ffffffff81559218>] create_pipe_files+0x138/0x2e0
[<ffffffff8126c793>] umd_setup+0x33/0x220
[<ffffffff81253574>] call_usermodehelper_exec_async+0xb4/0x1b0
[<ffffffff8100227f>] ret_from_fork+0x1f/0x30

After the UMD process exits, the pipe_to_umh/pipe_from_umh and
tgid need to be released.

Fixes: d71fa5c9763c ("bpf: Add kernel module with user mode driver that populates bpffs.")
Reported-by: syzbot+44908bb56d2bfe56b28e@syzkaller.appspotmail.com
Signed-off-by: Zqiang <qiang.zhang@windriver.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210317030915.2865-1-qiang.zhang@windriver.com

umd: Stop using split_argv

There is exactly one argument so there is nothing to split. All
split_argv does now is cause confusion and avoid the need for a cast
when passing a "const char *" string to call_usermodehelper_setup.

So avoid confusion and the possibility of an odd driver name causing
problems by just using a fixed argv array with a cast in the call to
call_usermodehelper_setup.

v1: https://lkml.kernel.org/r/87sged3a9n.fsf_-_@x220.int.ebiederm.org
Link: https://lkml.kernel.org/r/20200702164140.4468-16-ebiederm@xmission.com
Acked-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

umd: Remove exit_umh

The bpfilter code no longer uses the umd_info.cleanup callback. This
callback is what exit_umh exists to call. So remove exit_umh and all
of it's associated booking.

v1: https://lkml.kernel.org/r/87bll6dlte.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87y2o53abg.fsf_-_@x220.int.ebiederm.org
Link: https://lkml.kernel.org/r/20200702164140.4468-15-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>

umd: Track user space drivers with struct pid

Use struct pid instead of user space pid values that are prone to wrap
araound.

In addition track the entire thread group instead of just the first
thread that is started by exec. There are no multi-threaded user mode
drivers today but there is nothing preclucing user drivers from being
multi-threaded, so it is just a good idea to track the entire process.

Take a reference count on the tgid's in question to make it possible
to remove exit_umh in a future change.

As a struct pid is available directly use kill_pid_info.

The prior process signalling code was iffy in using a userspace pid
known to be in the initial pid namespace and then looking up it's task
in whatever the current pid namespace is. It worked only because
kernel threads always run in the initial pid namespace.

As the tgid is now refcounted verify the tgid is NULL at the start of
fork_usermode_driver to avoid the possibility of silent pid leaks.

v1: https://lkml.kernel.org/r/87mu4qdlv2.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/a70l4oy8.fsf_-_@x220.int.ebiederm.org
Link: https://lkml.kernel.org/r/20200702164140.4468-12-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>

umd: Transform fork_usermode_blob into fork_usermode_driver

Instead of loading a binary blob into a temporary file with
shmem_kernel_file_setup load a binary blob into a temporary tmpfs
filesystem. This means that the blob can be stored in an init section
and discared, and it means the binary blob will have a filename so can
be executed normally.

The only tricky thing about this code is that in the helper function
blob_to_mnt __fput_sync is used. That is because a file can not be
executed if it is still open for write, and the ordinary delayed close
for kernel threads does not happen soon enough, which causes the
following exec to fail. The function umd_load_blob is not called with
any locks so this should be safe.

Executing the blob normally winds up correcting several problems with
the user mode driver code discovered by Tetsuo Handa[1]. By passing
an ordinary filename into the exec, it is no longer necessary to
figure out how to turn a O_RDWR file descriptor into a properly
referende counted O_EXEC file descriptor that forbids all writes. For
path based LSMs there are no new special cases.

[1] https://lore.kernel.org/linux-fsdevel/2a8775b4-1dd5-9d5c-aa42-9872445e0942@i-love.sakura.ne.jp/
v1: https://lkml.kernel.org/r/87d05mf0j9.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87wo3p4p35.fsf_-_@x220.int.ebiederm.org
Link: https://lkml.kernel.org/r/20200702164140.4468-8-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>

umd: Rename umd_info.cmdline umd_info.driver_name

The only thing supplied in the cmdline today is the driver name so
rename the field to clarify the code.

As this value is always supplied stop trying to handle the case of
a NULL cmdline.

Additionally since we now have a name we can count on use the
driver_name any place where the code is looking for a name
of the binary.

v1: https://lkml.kernel.org/r/87imfef0k3.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87366d63os.fsf_-_@x220.int.ebiederm.org
Link: https://lkml.kernel.org/r/20200702164140.4468-7-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>

umd: For clarity rename umh_info umd_info

This structure is only used for user mode drivers so change
the prefix from umh to umd to make that clear.

v1: https://lkml.kernel.org/r/87o8p6f0kw.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/878sg563po.fsf_-_@x220.int.ebiederm.org
Link: https://lkml.kernel.org/r/20200702164140.4468-6-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>