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From: Steven Rostedt <rostedt@goodmis.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Beau Belgrave <beaub@linux.microsoft.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-trace-kernel@vger.kernel.org,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>, bpf <bpf@vger.kernel.org>,
	David Vernet <void@manifault.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	dthaler@microsoft.com, brauner@kernel.org, hch@infradead.org
Subject: Re: [PATCH] tracing/user_events: Run BPF program if attached
Date: Tue, 16 May 2023 21:26:58 -0400	[thread overview]
Message-ID: <20230516212658.2f5cc2c6@gandalf.local.home> (raw)
In-Reply-To: <20230517003628.aqqlvmzffj7fzzoj@MacBook-Pro-8.local>

On Tue, 16 May 2023 17:36:28 -0700
Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:


> "
> The user that will generate events must have x access to the tracing directory, e.g. chmod a+x /sys/kernel/tracing
> The user that will generate events must have rw access to the tracing/user_events_data file, e.g. chmod a+rw /sys/kernel/tracing/user_events_data
> "
> So any unpriv user can create and operate user events.
> Including seeing and enabling other user's user_events with 'ls/echo/cat' in tracefs.

It can see user_events_data, but x only gives you access into the directory.
It does not get you the contents of the files within the directory. The
above only gives access to the user_events_data. Which is to create events.

I recommended using groups and not giving access to all tasks.

> 
> Looks like user events were designed with intention to be unprivileged.
> When I looked at kernel/trace/trace_events_user.c I assumed root.
> I doubt other people reviewed it from security perspective.
> 
> Recommending "chmod a+rw /sys/kernel/tracing/user_events_data" doesn't sound like a good idea.
> 
> For example, I think the following is possible:
> fd = open("/sys/kernel/tracing/user_events_data")
> ioclt(fd, DIAG_IOCSDEL)
>   user_events_ioctl_del
>      delete_user_event(info->group, name);
> 
> 'info' is different for every FD, but info->group is the same for all users/processes/fds,
> because only one global init_group is created.
> So one user can unregister other user event by knowing 'name'.
> A security hole, no?
> 
> > and libside [2] will also help here.  
> 
> > [2] https://github.com/compudj/libside  
> 
> That's an interesting project. It doesn't do any user_events access afaict,

I'll let Beau answer the rest.

-- Steve



  parent reply	other threads:[~2023-05-17  1:27 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-05-08 16:37 [PATCH] tracing/user_events: Run BPF program if attached Beau Belgrave
2023-05-09 15:24 ` Alexei Starovoitov
2023-05-09 17:01   ` Steven Rostedt
2023-05-09 20:30     ` Steven Rostedt
2023-05-09 20:42       ` Steven Rostedt
2023-05-15 16:57       ` Alexei Starovoitov
2023-05-15 18:33         ` Steven Rostedt
2023-05-15 19:35           ` Beau Belgrave
2023-05-15 21:38             ` Steven Rostedt
2023-05-15 19:24         ` Beau Belgrave
2023-05-15 21:57           ` Steven Rostedt
2023-05-17  0:36           ` Alexei Starovoitov
2023-05-17  0:56             ` Linus Torvalds
2023-05-17  1:46               ` Linus Torvalds
2023-05-17  2:29                 ` Steven Rostedt
2023-05-17  3:03                   ` Linus Torvalds
2023-05-17 17:22                     ` Beau Belgrave
2023-05-17 18:15                       ` Linus Torvalds
2023-05-17 19:07                         ` Beau Belgrave
2023-05-17 19:26                           ` Linus Torvalds
2023-05-17 19:36                             ` Beau Belgrave
2023-05-17 19:36                             ` Linus Torvalds
2023-05-17 19:37                               ` Linus Torvalds
2023-05-17 23:00                                 ` Beau Belgrave
2023-05-17 23:14                                   ` Linus Torvalds
2023-05-17 23:25                                     ` Steven Rostedt
2023-05-18  0:14                                       ` Beau Belgrave
2023-05-18  0:23                                         ` Linus Torvalds
2023-05-17 20:08                               ` Linus Torvalds
2023-05-17  1:26             ` Steven Rostedt [this message]
2023-05-17 16:50               ` Beau Belgrave
2023-05-18  0:10                 ` Alexei Starovoitov
2023-05-18  0:19                   ` Beau Belgrave
2023-05-18  0:56                     ` Alexei Starovoitov
2023-05-18  1:18                       ` Beau Belgrave
2023-05-18  2:08                         ` Steven Rostedt
2023-05-18  3:14                           ` Alexei Starovoitov
2023-05-18 13:36                             ` Steven Rostedt
2023-05-18 17:28                               ` Beau Belgrave
2023-06-01  9:46                   ` Christian Brauner
2023-06-01 15:24                     ` Beau Belgrave
2023-06-01 15:57                       ` Christian Brauner
2023-06-01 16:29                         ` Beau Belgrave
2023-06-06 13:37                           ` Masami Hiramatsu
2023-06-06 17:05                             ` Beau Belgrave
2023-06-07 14:07                               ` Masami Hiramatsu
2023-06-07 19:26                                 ` Beau Belgrave
2023-06-08  0:25                                   ` Masami Hiramatsu
2023-05-17 17:51             ` Beau Belgrave
2023-06-06 13:57             ` Masami Hiramatsu
2023-06-06 16:57               ` Andrii Nakryiko
2023-06-06 20:57                 ` Beau Belgrave

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