Date: Mon, 3 Jul 2023 15:50:32 +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



6/22/2023 1:18 PM, Mickaël Salaün пишет:
> 
> 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.

   Stephen Rothwell sent a few warnings he got with powerpc 
pseries_le_defconfig. Do I need to fix it in V12 patch? How can I handle 
it cause no warnings in current .config?
> 
> 
>> 
>>>
>>> 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.
> 
  Thank you!!
> 
>>>
>>>>      - 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
>>>>>>>
>>>>> .
>>> .
> .

Powered by blists - more mailing lists