Date: Thu, 22 Jun 2023 11:00:25 +0300
From: "Konstantin Meskhidze (A)" <konstantin.meskhidze@...wei.com>
To: Mickaël Salaün <mic@...ikod.net>,
	Günther Noack <gnoack@...gle.com>
CC: <willemdebruijn.kernel@...il.com>, <gnoack3000@...il.com>,
	<linux-security-module@...r.kernel.org>, <netdev@...r.kernel.org>,
	<netfilter-devel@...r.kernel.org>, <yusongping@...wei.com>,
	<artem.kuzin@...wei.com>
Subject: Re: [PATCH v11 11/12] samples/landlock: Add network demo



6/19/2023 9:19 PM, Mickaël Salaün пишет:
> 
> On 19/06/2023 16:24, Konstantin Meskhidze (A) wrote:
>> 
>> 
>> 6/13/2023 11:38 PM, Mickaël Salaün пишет:
>>>
>>> On 13/06/2023 12:54, Konstantin Meskhidze (A) wrote:
>>>>
>>>>
>>>> 6/6/2023 6:17 PM, Günther Noack пишет:
>>>>> Hi Konstantin!
>>>>>
>>>>> Apologies if some of this was discussed before, in this case,
>>>>> Mickaël's review overrules my opinions from the sidelines ;)
>>>>>
>>>>> On Tue, May 16, 2023 at 12:13:38AM +0800, Konstantin Meskhidze wrote:
>>>>>> This commit adds network demo. It's possible to allow a sandboxer to
>>>>>> bind/connect to a list of particular ports restricting network
>>>>>> actions to the rest of ports.
>>>>>>
>>>>>> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@...wei.com>
>>>>>
>>>>>
>>>>>> diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
>>>>>> index e2056c8b902c..b0250edb6ccb 100644
>>>>>> --- a/samples/landlock/sandboxer.c
>>>>>> +++ b/samples/landlock/sandboxer.c
>>>>>
>>>>> ...
>>>>>
>>>>>> +static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
>>>>>> +				const __u64 allowed_access)
>>>>>> +{
>>>>>> +	int num_ports, i, ret = 1;
>>>>>
>>>>> I thought the convention was normally to set ret = 0 initially and to
>>>>> override it in case of error, rather than the other way around?
>>>
>>> Which convention? In this case, by default the return code is an error.
>>>
>>>
>>>>>
>>>>      Well, I just followed Mickaёl's way of logic here. >
>>>>
>>>>>> +	char *env_port_name;
>>>>>> +	struct landlock_net_service_attr net_service = {
>>>>>> +		.allowed_access = allowed_access,
>>>>>> +		.port = 0,
>>>>>> +	};
>>>>>> +
>>>>>> +	env_port_name = getenv(env_var);
>>>>>> +	if (!env_port_name)
>>>>>> +		return 0;
>>>>>> +	env_port_name = strdup(env_port_name);
>>>>>> +	unsetenv(env_var);
>>>>>> +	num_ports = parse_port_num(env_port_name);
>>>>>> +
>>>>>> +	if (num_ports == 1 && (strtok(env_port_name, ENV_PATH_TOKEN) == NULL)) {
>>>>>> +		ret = 0;
>>>>>> +		goto out_free_name;
>>>>>> +	}
>>>>>
>>>>> I don't understand why parse_port_num and strtok are necessary in this
>>>>> program. The man-page for strsep(3) describes it as a replacement to
>>>>> strtok(3) (in the HISTORY section), and it has a very short example
>>>>> for how it is used.
>>>>>
>>>>> Wouldn't it work like this as well?
>>>>>
>>>>> while ((strport = strsep(&env_port_name, ":"))) {
>>>>>      net_service.port = atoi(strport);
>>>>>      /* etc */
>>>>> }
>>>>
>>>>      Thanks for a tip. I think it's a better solution here. Now this
>>>> commit is in Mickaёl's -next branch. I could send a one-commit patch later.
>>>> Mickaёl, what do you think?
>>>
>>> I removed this series from -next because there is some issues (see the
>>> bot's emails), but anyway, this doesn't mean these patches don't need to
>>> be changed, they do. The goal of -next is to test more widely a patch
>>> series and get more feedbacks, especially from bots. When this series
>>> will be fully ready (and fuzzed with syzkaller), I'll push it to Linus
>>> Torvalds.
>>>
>>> I'll review the remaining tests and sample code this week, but you can
>>> still take into account the documentation review.
>> 
>>    Hi, Mickaёl.
>> 
>>    I have a few quetions?
>>     - Are you going to fix warnings for bots, meanwhile I run syzcaller?
> 
> No, you need to fix that with the next series (except the Signed-off-by
> warnings).

  Hi, Mickaёl.
   As I understand its possible to check bots warnings just after you 
push the next V12 series again into your -next branch???

> 
> What is your status on syzkaller? Do you need some help? I can write the
> tests if it's too much.
> 
   Sorry. To be honest I'm busy with another project. I dont know how 
much time it will take for me to set up and run syzkaller. I need your 
help here please, how you do this, some roadmap.
> 
>>     - I will fix documentation and sandbox demo and sent patch v12?
> 
> Yes please. Let me a few days to send more reviews.
> 
   Ok. Sure.
>> 
>>>
>>>
>>>>
>>>>>
>>>>>> +
>>>>>> +	for (i = 0; i < num_ports; i++) {
>>>>>> +		net_service.port = atoi(strsep(&env_port_name, ENV_PATH_TOKEN));
>>>>>
>>>>> Naming of ENV_PATH_TOKEN:
>>>>> This usage is not related to paths, maybe rename the variable?
>>>>> It's also technically not the token, but the delimiter.
>>>>>
>>>>     What do you think of ENV_PORT_TOKEN or ENV_PORT_DELIMITER???
>>>
>>> You can rename ENV_PATH_TOKEN to ENV_DELIMITER for the FS and network parts.
>>>
>>      Ok. Got it.
>>>
>>>>
>>>>>> +		if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_SERVICE,
>>>>>> +				      &net_service, 0)) {
>>>>>> +			fprintf(stderr,
>>>>>> +				"Failed to update the ruleset with port \"%lld\": %s\n",
>>>>>> +				net_service.port, strerror(errno));
>>>>>> +			goto out_free_name;
>>>>>> +		}
>>>>>> +	}
>>>>>> +	ret = 0;
>>>>>> +
>>>>>> +out_free_name:
>>>>>> +	free(env_port_name);
>>>>>> +	return ret;
>>>>>> +}
>>>>>
>>>>>
>>>>>>    		fprintf(stderr,
>>>>>>    			"Launch a command in a restricted environment.\n\n");
>>>>>> -		fprintf(stderr, "Environment variables containing paths, "
>>>>>> -				"each separated by a colon:\n");
>>>>>> +		fprintf(stderr,
>>>>>> +			"Environment variables containing paths and ports "
>>>>>> +			"each separated by a colon:\n");
>>>>>>    		fprintf(stderr,
>>>>>>    			"* %s: list of paths allowed to be used in a read-only way.\n",
>>>>>>    			ENV_FS_RO_NAME);
>>>>>>    		fprintf(stderr,
>>>>>> -			"* %s: list of paths allowed to be used in a read-write way.\n",
>>>>>> +			"* %s: list of paths allowed to be used in a read-write way.\n\n",
>>>>>>    			ENV_FS_RW_NAME);
>>>>>> +		fprintf(stderr,
>>>>>> +			"Environment variables containing ports are optional "
>>>>>> +			"and could be skipped.\n");
>>>>>
>>>>> As it is, I believe the program does something different when I'm
>>>>> setting these to the empty string (ENV_TCP_BIND_NAME=""), compared to
>>>>> when I'm unsetting them?
>>>>>
>>>>> I think the case where we want to forbid all handle-able networking is
>>>>> a legit and very common use case - it could be clearer in the
>>>>> documentation how this is done with the tool. (And maybe the interface
>>>>> could be something more explicit than setting the environment variable
>>>>> to empty?)
>>>
>>> I'd like to keep it simple, and it should be seen as an example code,
>>> not a full-feature sandboxer, but still a consistent and useful one.
>>> What would you suggest?
>>>
>>> This sandboxer tool relies on environment variables for its
>>> configuration. This is definitely not a good fit for all use cases, but
>>> I think it is simple and flexible enough. One use case might be to
>>> export a set of environment variables and simply call this tool. I'd
>>> prefer to not deal with argument parsing, but maybe that was too
>>> simplistic? We might want to revisit this approach but probably not with
>>> this series.
>>>
>>>
>>>>>
>>>>>
>>>>>> +	/* Removes bind access attribute if not supported by a user. */
>>>>>> +	env_port_name = getenv(ENV_TCP_BIND_NAME);
>>>>>> +	if (!env_port_name) {
>>>>>> +		ruleset_attr.handled_access_net &=
>>>>>> +			~LANDLOCK_ACCESS_NET_BIND_TCP;
>>>>>> +	}
>>>>>> +	/* Removes connect access attribute if not supported by a user. */
>>>>>> +	env_port_name = getenv(ENV_TCP_CONNECT_NAME);
>>>>>> +	if (!env_port_name) {
>>>>>> +		ruleset_attr.handled_access_net &=
>>>>>> +			~LANDLOCK_ACCESS_NET_CONNECT_TCP;
>>>>>> +	}
>>>>>
>>>>> This is the code where the program does not restrict network usage,
>>>>> if the corresponding environment variable is not set.
>>>>
>>>>      Yep. Right.
>>>>>
>>>>> It's slightly inconsistent with what this tool does for filesystem
>>>>> paths. - If you don't specify any file paths, it will still restrict
>>>>> file operations there, independent of whether that env variable was
>>>>> set or not.  (Apologies if it was discussed before.)
>>>>
>>>>     Mickaёl wanted to make network ports optional here.
>>>>     Please check:
>>>>    
>>>> https://lore.kernel.org/linux-security-module/179ac2ee-37ff-92da-c381-c2c716725045@digikod.net/
>>>
>>> Right, the rationale is for compatibility with the previous version of
>>> this tool. We should not break compatibility when possible. A comment
>>> should explain the rationale though.
>>>
>>>>
>>>> https://lore.kernel.org/linux-security-module/fe3bc928-14f8-5e2b-359e-9a87d6cf5b01@digikod.net/
>>>>>
>>>>> —Günther
>>>>>
>>> .
> .

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