Date: Thu, 22 Jun 2023 12:18:15 +0200
From: Mickaël Salaün <mic@...ikod.net>
To: "Konstantin Meskhidze (A)" <konstantin.meskhidze@...wei.com>,
 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


On 22/06/2023 10:00, Konstantin Meskhidze (A) wrote:
> 
> 
> 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???

Yes, we get bot warnings on the -next tree, but the command that 
generate it should be reproducible.


> 
>>
>> 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.

Ok, no worries, I have it set up so I'll take care of it and keep you in 
the loop with your GitHub account.


>>
>>>      - 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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