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From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: "Eric W. Biederman" <ebiederm@xmission.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Casey Schaufler <casey@schaufler-ca.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	linux-kernel@vger.kernel.org, David Miller <davem@davemloft.net>,
	Greg Kroah-Hartman <greg@kroah.com>,
	Kees Cook <keescook@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexei Starovoitov <ast@kernel.org>, bpf <bpf@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	Gary Lin <GLin@suse.com>, Bruno Meneguele <bmeneg@redhat.com>,
	LSM List <linux-security-module@vger.kernel.org>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH v2 00/15] Make the user mode driver code a better citizen
Date: Fri, 3 Jul 2020 22:19:17 +0900
Message-ID: <d0266a24-dfab-83d0-e178-aa67c9f5ebc0@i-love.sakura.ne.jp> (raw)
In-Reply-To: <87h7upucqi.fsf@x220.int.ebiederm.org>

On 2020/07/02 22:08, Eric W. Biederman wrote:
>> By the way, commit 4a9d4b024a3102fc ("switch fput to task_work_add") says
>> that use of flush_delayed_fput() has to be careful. Al, is it safe to call
>> flush_delayed_fput() from blob_to_mnt() from umd_load_blob() (which might be
>> called from both kernel thread and from process context (e.g. init_module()
>> syscall by /sbin/insmod )) ?
> 
> And __fput_sync needs to be even more careful.
> umd_load_blob is called in these changes without any locks held.

But where is the guarantee that a thread which called flush_delayed_fput() waits for
the completion of processing _all_ "struct file" linked into delayed_fput_list ?
If some other thread or delayed_fput_work (scheduled by fput_many()) called
flush_delayed_fput() between blob_to_mnt()'s fput(file) and flush_delayed_fput()
sequence? blob_to_mnt()'s flush_delayed_fput() can miss the "struct file" which
needs to be processed before execve(), can't it?

Also, I don't know how convoluted the dependency of all "struct file" linked into
delayed_fput_list might be, for there can be "struct file" which will not be a
simple close of tmpfs file created by blob_to_mnt()'s file_open_root() request.

On the other hand, although __fput_sync() cannot be called from !PF_KTHREAD threads,
there is a guarantee that __fput_sync() waits for the completion of "struct file"
which needs to be flushed before execve(), isn't there?

> 
> We fundamentally AKA in any correct version of this code need to flush
> the file descriptor before we call exec or exec can not open it a
> read-only denying all writes from any other opens.
> 
> The use case of flush_delayed_fput is exactly the same as that used
> when loading the initramfs.

When loading the initramfs, the number of threads is quite few (which
means that the possibility of hitting the race window and convoluted
dependency is small).

But like EXPORT_SYMBOL_GPL(umd_load_blob) indicates, blob_to_mnt()'s
flush_delayed_fput() might be called after many number of threads already
started running.



On 2020/07/03 1:02, Eric W. Biederman wrote:
>>>> On 2020/06/30 21:29, Eric W. Biederman wrote:
>>>>> Hmm.  The wake up happens just of tgid->wait_pidfd happens just before
>>>>> release_task is called so there is a race.  As it is possible to wake
>>>>> up and then go back to sleep before pid_has_task becomes false.
>>>>
>>>> What is the reason we want to wait until pid_has_task() becomes false?
>>>>
>>>> - wait_event(tgid->wait_pidfd, !pid_has_task(tgid, PIDTYPE_TGID));
>>>> + while (!wait_event_timeout(tgid->wait_pidfd, !pid_has_task(tgid, PIDTYPE_TGID), 1));
>>>
>>> So that it is safe to call bpfilter_umh_cleanup.  The previous code
>>> performed the wait by having a callback in do_exit.
>>
>> But bpfilter_umh_cleanup() does only
>>
>> 	fput(info->pipe_to_umh);
>> 	fput(info->pipe_from_umh);
>> 	put_pid(info->tgid);
>> 	info->tgid = NULL;
>>
>> which is (I think) already safe regardless of the usermode process because
>> bpfilter_umh_cleanup() merely closes one side of two pipes used between
>> two processes and forgets about the usermode process.
> 
> It is not safe.
> 
> Baring bugs there is only one use of shtudown_umh that matters.  The one
> in fini_umh.  The use of the file by the mm must be finished before
> umd_unload_blob.  AKA unmount.  Which completely frees the filesystem.

Do we really need to mount upon umd_load_blob() and unmount upon umd_unload_blob() ?
LSM modules might prefer only one instance of filesystem for umd blobs.

For pathname based LSMs, since that filesystem is not visible from mount tree, only
info->driver_name can be used for distinction. Therefore, one instance of filesystem
with files created with file_open_root(O_CREAT | O_WRONLY | O_EXCL) might be preferable.

For inode based LSMs, reusing one instance of filesystem created upon early boot might
be convenient for labeling.

Also, we might want a dedicated filesystem (say, "umdfs") instead of regular tmpfs in
order to implement protections without labeling files. Then, we might also be able to
implement minimal protections without LSMs.


  reply index

Thread overview: 194+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200329005528.xeKtdz2A0%akpm@linux-foundation.org>
     [not found] ` <13fb3ab7-9ab1-b25f-52f2-40a6ca5655e1@i-love.sakura.ne.jp>
     [not found]   ` <202006051903.C44988B@keescook>
2020-06-06 19:20     ` [RFC][PATCH] net/bpfilter: Remove this broken and apparently unmantained Eric W. Biederman
2020-06-06 20:19       ` Alexei Starovoitov
2020-06-06 22:33         ` Linus Torvalds
2020-06-07  1:49           ` Alexei Starovoitov
2020-06-07  2:19             ` Linus Torvalds
2020-06-07 16:09               ` Eric W. Biederman
2020-06-08 16:20               ` Alexei Starovoitov
2020-06-08 16:40                 ` Greg KH
2020-06-08 18:35                 ` Kees Cook
2020-06-09  1:26                   ` Alexei Starovoitov
2020-06-09 15:37                     ` Kees Cook
2020-06-09 19:51                 ` Eric W. Biederman
2020-06-07  2:31             ` Tetsuo Handa
2020-06-08 16:23               ` Alexei Starovoitov
2020-06-08 23:22                 ` Tetsuo Handa
2020-06-09  1:28                   ` Alexei Starovoitov
2020-06-09  5:29                     ` Tetsuo Handa
2020-06-09 22:32                       ` Alexei Starovoitov
2020-06-09 23:30                         ` Tetsuo Handa
2020-06-10  0:05                           ` Alexei Starovoitov
2020-06-10  3:08                             ` Tetsuo Handa
2020-06-10  3:32                               ` Alexei Starovoitov
2020-06-10  7:30                                 ` Tetsuo Handa
2020-06-10 16:24                                   ` Casey Schaufler
2020-06-09 20:02                 ` Eric W. Biederman
2020-06-09 23:56                   ` Alexei Starovoitov
2020-06-10 21:12                     ` Eric W. Biederman
2020-06-11 23:31                       ` Alexei Starovoitov
2020-06-12  0:57                         ` Tetsuo Handa
2020-06-13  3:38                           ` Alexei Starovoitov
2020-06-13  4:22                             ` Tetsuo Handa
2020-06-13 14:08                         ` Eric W. Biederman
2020-06-13 15:33                           ` Alexei Starovoitov
2020-06-13 16:14                             ` Alexei Starovoitov
2020-06-14 14:51                               ` Eric W. Biederman
2020-06-16  1:55                                 ` Alexei Starovoitov
2020-06-16 16:21                                   ` Alexei Starovoitov
2020-06-23 18:04                                   ` Eric W. Biederman
2020-06-23 18:35                                     ` Alexei Starovoitov
2020-06-23 18:53                                       ` Eric W. Biederman
2020-06-23 19:40                                         ` Alexei Starovoitov
2020-06-24  1:51                                           ` Tetsuo Handa
2020-06-24  4:00                                             ` Alexei Starovoitov
2020-06-24  4:58                                               ` Tetsuo Handa
2020-06-24  6:39                                                 ` Alexei Starovoitov
2020-06-24  7:05                                                   ` Tetsuo Handa
2020-06-24 15:41                                                     ` Casey Schaufler
2020-06-24 17:54                                                       ` Alexei Starovoitov
2020-06-24 19:48                                                         ` Casey Schaufler
2020-06-24  6:05                                               ` Alexei Starovoitov
2020-06-24 14:18                                                 ` Alexei Starovoitov
2020-06-24 12:13                                           ` Eric W. Biederman
2020-06-24 14:26                                             ` Alexei Starovoitov
2020-06-24 23:14                                               ` Tetsuo Handa
2020-06-25  1:35                                                 ` Alexei Starovoitov
2020-06-25  6:38                                                   ` Tetsuo Handa
2020-06-25  9:57                                                     ` Greg KH
2020-06-25 11:03                                                       ` Tetsuo Handa
2020-06-25 12:07                                                         ` Greg KH
2020-06-25 14:21                                                           ` Tetsuo Handa
2020-06-25 19:34                                                           ` David Miller
2020-06-26  1:36                                                             ` Linus Torvalds
2020-06-26  1:51                                                               ` Alexei Starovoitov
2020-06-26  4:58                                                                 ` Tetsuo Handa
2020-06-26  5:41                                                                   ` Alexei Starovoitov
2020-06-26  6:20                                                                     ` Tetsuo Handa
2020-06-26  6:39                                                                       ` Alexei Starovoitov
2020-06-26 12:51                                                               ` [PATCH 00/14] Make the user mode driver code a better citizen Eric W. Biederman
2020-06-26 12:53                                                                 ` [PATCH 01/14] umh: Capture the pid in umh_pipe_setup Eric W. Biederman
2020-06-26 12:53                                                                 ` [PATCH 02/14] umh: Move setting PF_UMH into umh_pipe_setup Eric W. Biederman
2020-06-26 12:54                                                                 ` [PATCH 03/14] umh: Rename the user mode driver helpers for clarity Eric W. Biederman
2020-06-26 12:54                                                                 ` [PATCH 04/14] umh: Remove call_usermodehelper_setup_file Eric W. Biederman
2020-06-26 12:55                                                                 ` [PATCH 05/14] umh: Separate the user mode driver and the user mode helper support Eric W. Biederman
2020-06-26 14:17                                                                   ` kernel test robot
2020-06-26 16:22                                                                   ` Tetsuo Handa
2020-06-26 16:45                                                                     ` Eric W. Biederman
2020-06-27  1:26                                                                       ` Tetsuo Handa
2020-06-27  4:21                                                                         ` Eric W. Biederman
2020-06-27  4:36                                                                           ` Tetsuo Handa
2020-06-26 12:55                                                                 ` [PATCH 06/14] umd: For clarity rename umh_info umd_info Eric W. Biederman
2020-06-26 15:37                                                                   ` Kees Cook
2020-06-26 16:31                                                                     ` Eric W. Biederman
2020-06-26 12:56                                                                 ` [PATCH 07/14] umd: Rename umd_info.cmdline umd_info.driver_name Eric W. Biederman
2020-06-26 12:56                                                                 ` [PATCH 08/14] umd: Transform fork_usermode_blob into fork_usermode_driver Eric W. Biederman
2020-06-26 12:57                                                                 ` [PATCH 09/14] umh: Stop calling do_execve_file Eric W. Biederman
2020-06-26 12:57                                                                 ` [PATCH 10/14] exec: Remove do_execve_file Eric W. Biederman
2020-06-26 12:58                                                                 ` [PATCH 11/14] bpfilter: Move bpfilter_umh back into init data Eric W. Biederman
2020-06-26 12:58                                                                 ` [PATCH 12/14] umd: Track user space drivers with struct pid Eric W. Biederman
2020-06-26 12:59                                                                 ` [PATCH 13/14] bpfilter: Take advantage of the facilities of " Eric W. Biederman
2020-06-26 12:59                                                                 ` [PATCH 14/14] umd: Remove exit_umh Eric W. Biederman
2020-06-26 13:48                                                                 ` [PATCH 00/14] Make the user mode driver code a better citizen Eric W. Biederman
2020-06-29 19:55                                                                   ` [PATCH v2 00/15] " Eric W. Biederman
2020-06-29 19:56                                                                     ` [PATCH v2 01/15] umh: Capture the pid in umh_pipe_setup Eric W. Biederman
2020-06-29 19:57                                                                     ` [PATCH v2 02/15] umh: Move setting PF_UMH into umh_pipe_setup Eric W. Biederman
2020-06-29 19:57                                                                     ` [PATCH v2 03/15] umh: Rename the user mode driver helpers for clarity Eric W. Biederman
2020-06-29 19:59                                                                     ` [PATCH v2 04/15] umh: Remove call_usermodehelper_setup_file Eric W. Biederman
2020-06-29 20:00                                                                     ` [PATCH v2 05/15] umh: Separate the user mode driver and the user mode helper support Eric W. Biederman
2020-06-30 16:58                                                                       ` Linus Torvalds
2020-07-01 17:18                                                                         ` Eric W. Biederman
2020-07-01 17:42                                                                           ` Alexei Starovoitov
2020-06-29 20:01                                                                     ` [PATCH v2 06/15] umd: For clarity rename umh_info umd_info Eric W. Biederman
2020-06-29 20:02                                                                     ` [PATCH v2 07/15] umd: Rename umd_info.cmdline umd_info.driver_name Eric W. Biederman
2020-06-29 20:03                                                                     ` [PATCH v2 08/15] umd: Transform fork_usermode_blob into fork_usermode_driver Eric W. Biederman
2020-06-29 20:03                                                                     ` [PATCH v2 09/15] umh: Stop calling do_execve_file Eric W. Biederman
2020-06-29 20:04                                                                     ` [PATCH v2 10/15] exec: Remove do_execve_file Eric W. Biederman
2020-06-30  5:43                                                                       ` Christoph Hellwig
2020-06-30 12:14                                                                         ` Eric W. Biederman
2020-06-30 13:38                                                                           ` Christoph Hellwig
2020-06-30 14:28                                                                             ` Eric W. Biederman
2020-06-30 16:55                                                                               ` Alexei Starovoitov
2020-06-29 20:05                                                                     ` [PATCH v2 11/15] bpfilter: Move bpfilter_umh back into init data Eric W. Biederman
2020-06-29 20:06                                                                     ` [PATCH v2 12/15] umd: Track user space drivers with struct pid Eric W. Biederman
2020-06-29 20:06                                                                     ` [PATCH v2 13/15] bpfilter: Take advantage of the facilities of " Eric W. Biederman
2020-06-29 20:07                                                                     ` [PATCH v2 14/15] umd: Remove exit_umh Eric W. Biederman
2020-06-29 20:08                                                                     ` [PATCH v2 15/15] umd: Stop using split_argv Eric W. Biederman
2020-06-29 22:12                                                                     ` [PATCH v2 00/15] Make the user mode driver code a better citizen Alexei Starovoitov
2020-06-30  1:13                                                                       ` Eric W. Biederman
2020-06-30  6:16                                                                         ` Tetsuo Handa
2020-06-30 12:29                                                                       ` Eric W. Biederman
2020-06-30 13:21                                                                         ` Tetsuo Handa
2020-07-02 13:08                                                                           ` Eric W. Biederman
2020-07-02 13:40                                                                             ` Tetsuo Handa
2020-07-02 16:02                                                                               ` Eric W. Biederman
2020-07-03 13:19                                                                                 ` Tetsuo Handa [this message]
2020-07-03 22:25                                                                                   ` Eric W. Biederman
2020-07-04  6:57                                                                                     ` Tetsuo Handa
2020-07-08  4:46                                                                                       ` Eric W. Biederman
2020-06-30 16:52                                                                         ` Alexei Starovoitov
2020-07-01 17:12                                                                           ` Eric W. Biederman
2020-07-02 16:40                                                                     ` [PATCH v3 00/16] " Eric W. Biederman
2020-07-02 16:41                                                                       ` [PATCH v3 01/16] umh: Capture the pid in umh_pipe_setup Eric W. Biederman
2020-07-02 16:41                                                                       ` [PATCH v3 02/16] umh: Move setting PF_UMH into umh_pipe_setup Eric W. Biederman
2020-07-02 16:41                                                                       ` [PATCH v3 03/16] umh: Rename the user mode driver helpers for clarity Eric W. Biederman
2020-07-02 16:41                                                                       ` [PATCH v3 04/16] umh: Remove call_usermodehelper_setup_file Eric W. Biederman
2020-07-02 16:41                                                                       ` [PATCH v3 05/16] umh: Separate the user mode driver and the user mode helper support Eric W. Biederman
2020-07-02 16:41                                                                       ` [PATCH v3 06/16] umd: For clarity rename umh_info umd_info Eric W. Biederman
2020-07-02 16:41                                                                       ` [PATCH v3 07/16] umd: Rename umd_info.cmdline umd_info.driver_name Eric W. Biederman
2020-07-02 16:41                                                                       ` [PATCH v3 08/16] umd: Transform fork_usermode_blob into fork_usermode_driver Eric W. Biederman
2020-07-02 16:41                                                                       ` [PATCH v3 09/16] umh: Stop calling do_execve_file Eric W. Biederman
2020-07-02 16:41                                                                       ` [PATCH v3 10/16] exec: Remove do_execve_file Eric W. Biederman
2020-07-08  6:35                                                                         ` Luis Chamberlain
2020-07-08 12:41                                                                           ` Luis Chamberlain
2020-07-08 13:08                                                                             ` Eric W. Biederman
2020-07-08 13:32                                                                               ` Luis Chamberlain
2020-07-12 21:02                                                                         ` Pavel Machek
2020-07-02 16:41                                                                       ` [PATCH v3 11/16] bpfilter: Move bpfilter_umh back into init data Eric W. Biederman
2020-07-02 16:41                                                                       ` [PATCH v3 12/16] umd: Track user space drivers with struct pid Eric W. Biederman
2020-07-02 16:41                                                                       ` [PATCH v3 13/16] exit: Factor thread_group_exited out of pidfd_poll Eric W. Biederman
2020-07-03 20:30                                                                         ` Alexei Starovoitov
2020-07-03 21:37                                                                           ` Eric W. Biederman
2020-07-04  0:03                                                                             ` Alexei Starovoitov
2020-07-04 15:50                                                                             ` Christian Brauner
2020-07-07 17:09                                                                               ` Eric W. Biederman
2020-07-08  0:05                                                                                 ` Daniel Borkmann
2020-07-08  3:50                                                                                   ` Eric W. Biederman
2020-07-04 16:00                                                                         ` Christian Brauner
2020-07-02 16:41                                                                       ` [PATCH v3 14/16] bpfilter: Take advantage of the facilities of struct pid Eric W. Biederman
2020-07-02 16:41                                                                       ` [PATCH v3 15/16] umd: Remove exit_umh Eric W. Biederman
2020-07-02 16:41                                                                       ` [PATCH v3 16/16] umd: Stop using split_argv Eric W. Biederman
2020-07-02 23:51                                                                       ` [PATCH v3 00/16] Make the user mode driver code a better citizen Tetsuo Handa
2020-07-09 22:05                                                                       ` [merged][PATCH " Eric W. Biederman
2020-07-14 19:42                                                                         ` Alexei Starovoitov
2020-07-08  5:20                                                                     ` [PATCH v2 00/15] " Luis Chamberlain
2020-06-26 14:10                                                                 ` [PATCH 00/14] " Greg Kroah-Hartman
2020-06-26 16:40                                                                 ` Alexei Starovoitov
2020-06-26 17:17                                                                   ` Eric W. Biederman
2020-06-26 18:22                                                                     ` Alexei Starovoitov
2020-06-27 11:38                                                                 ` Tetsuo Handa
2020-06-27 12:59                                                                   ` Eric W. Biederman
2020-06-27 13:57                                                                     ` Tetsuo Handa
2020-06-28 19:44                                                                       ` Alexei Starovoitov
2020-06-29  2:20                                                                         ` Tetsuo Handa
2020-06-29 20:19                                                                           ` Eric W. Biederman
2020-06-30  6:28                                                                             ` Tetsuo Handa
2020-06-30 12:32                                                                               ` Eric W. Biederman
2020-06-30 16:48                                                                               ` Alexei Starovoitov
2020-06-30 21:54                                                                                 ` Tetsuo Handa
2020-06-30 21:57                                                                                   ` Alexei Starovoitov
2020-06-30 22:58                                                                                     ` Tetsuo Handa
2020-06-25 12:56                                                 ` [RFC][PATCH] net/bpfilter: Remove this broken and apparently unmantained Stephen Smalley
2020-06-25 13:25                                                   ` Greg Kroah-Hartman
2020-06-25 14:26                                                     ` Stephen Smalley
2020-06-25 14:36                                                       ` Stephen Smalley
2020-06-25 15:21                                                       ` Tetsuo Handa
2020-06-25 16:03                                                         ` Stephen Smalley
2020-06-25 16:06                                                         ` Casey Schaufler
2020-06-26 11:30                                               ` Eric W. Biederman
2020-06-07  5:58             ` Eric W. Biederman
2020-06-07 11:56               ` Eric W. Biederman
2020-06-08 16:35                 ` Alexei Starovoitov
2020-06-08 16:33               ` Alexei Starovoitov
2020-06-06 20:43       ` Matthew Wilcox
2020-06-07 15:51         ` Eric W. Biederman
2020-06-07  1:13       ` Tetsuo Handa

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