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Date: Thu, 19 May 2022 16:33:20 +0300
From: Konstantin Meskhidze <konstantin.meskhidze@...wei.com>
To: Mickaël Salaün <mic@...ikod.net>
CC: <willemdebruijn.kernel@...il.com>,
<linux-security-module@...r.kernel.org>, <netdev@...r.kernel.org>,
<netfilter-devel@...r.kernel.org>, <yusongping@...wei.com>,
<anton.sirazetdinov@...wei.com>
Subject: Re: [PATCH v5 15/15] samples/landlock: adds network demo
5/17/2022 12:19 PM, Mickaël Salaün пишет:
>
>
> On 16/05/2022 17:20, Konstantin Meskhidze wrote:
>> This commit adds network demo. It's possible to
>> allow a sandoxer to bind/connect to a list of
>> particular ports restricting networks actions to
>> the rest of ports.
>>
>> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@...wei.com>
>> ---
>>
>> Changes since v4:
>> * Adds ENV_TCP_BIND_NAME "LL_TCP_BIND" and
>> ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT" variables
>> to insert TCP ports.
>> * Renames populate_ruleset() to populate_ruleset_fs().
>> * Adds populate_ruleset_net() and parse_port_num() helpers.
>> * Refactoring main() to support network sandboxing.
>>
>> ---
>> samples/landlock/sandboxer.c | 105 +++++++++++++++++++++++++++++++----
>> security/landlock/ruleset.h | 4 +-
>> 2 files changed, 95 insertions(+), 14 deletions(-)
>>
>> diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
>> index 3e404e51ec64..4006c42eec1c 100644
>> --- a/samples/landlock/sandboxer.c
>> +++ b/samples/landlock/sandboxer.c
>> @@ -51,6 +51,8 @@ static inline int landlock_restrict_self(const int
>> ruleset_fd,
>>
>> #define ENV_FS_RO_NAME "LL_FS_RO"
>> #define ENV_FS_RW_NAME "LL_FS_RW"
>> +#define ENV_TCP_BIND_NAME "LL_TCP_BIND"
>> +#define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT"
>> #define ENV_PATH_TOKEN ":"
>>
>> static int parse_path(char *env_path, const char ***const path_list)
>> @@ -71,6 +73,20 @@ static int parse_path(char *env_path, const char
>> ***const path_list)
>> return num_paths;
>> }
>>
>> +static int parse_port_num(char *env_port)
>> +{
>> + int i, num_ports = 0;
>> +
>> + if (env_port) {
>> + num_ports++;
>> + for (i = 0; env_port[i]; i++) {
>> + if (env_port[i] == ENV_PATH_TOKEN[0])
>> + num_ports++;
>> + }
>> + }
>> + return num_ports;
>> +}
>> +
>> /* clang-format off */
>>
>> #define ACCESS_FILE ( \
>> @@ -80,7 +96,7 @@ static int parse_path(char *env_path, const char
>> ***const path_list)
>>
>> /* clang-format on */
>>
>> -static int populate_ruleset(const char *const env_var, const int
>> ruleset_fd,
>> +static int populate_ruleset_fs(const char *const env_var, const int
>> ruleset_fd,
>> const __u64 allowed_access)
>> {
>> int num_paths, i, ret = 1;
>> @@ -142,6 +158,49 @@ static int populate_ruleset(const char *const
>> env_var, const int ruleset_fd,
>> return ret;
>> }
>>
>> +static int populate_ruleset_net(const char *const env_var,
>> + const int ruleset_fd,
>> + const __u64 allowed_access)
>> +{
>> + int num_ports, i, ret = 1;
>> + char *env_port_name;
>> + struct landlock_net_service_attr net_service = {
>> + .allowed_access = 0,
>> + .port = 0,
>> + };
>> +
>> + env_port_name = getenv(env_var);
>> + if (!env_port_name) {
>> + /* Prevents users to forget a setting. */
>> + fprintf(stderr, "Missing environment variable %s\n", env_var);
>> + return 1;
>
> I think network ports should be optional to be able to test without that
> (and not break compatibility). You can pass &ruleset_attr as argument to
> update it accordingly:
> - without environment variable: no network restriction;
> - with empty environment variable: all connect (or bind) denied;
> - otherwise: only allow the listed ports.
>
Great. That makes sense. Cause anyway fs restrictions are major ones.
>
>> + }
>> + 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;
>> + }
>> +
>> + for (i = 0; i < num_ports; i++) {
>> + net_service.allowed_access = allowed_access;
>> + net_service.port = atoi(strsep(&env_port_name, ENV_PATH_TOKEN));
>> + if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_SERVICE,
>> + &net_service, 0)) {
>> + fprintf(stderr, "Failed to update the ruleset with port
>> \"%d\": %s\n",
>> + net_service.port, strerror(errno));
>> + goto out_free_name;
>> + }
>> + }
>> + ret = 0;
>> +
>> +out_free_name:
>> + free(env_port_name);
>> + return ret;
>> +}
>> +
>> /* clang-format off */
>>
>> #define ACCESS_FS_ROUGHLY_READ ( \
>> @@ -173,19 +232,24 @@ int main(const int argc, char *const argv[],
>> char *const *const envp)
>> char *const *cmd_argv;
>> int ruleset_fd, abi;
>> __u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ,
>> - access_fs_rw = ACCESS_FS_ROUGHLY_READ |
>> ACCESS_FS_ROUGHLY_WRITE;
>> + access_fs_rw = ACCESS_FS_ROUGHLY_READ |
>> ACCESS_FS_ROUGHLY_WRITE,
>> + access_net_tcp = LANDLOCK_ACCESS_NET_BIND_TCP |
>> + LANDLOCK_ACCESS_NET_CONNECT_TCP;
>> struct landlock_ruleset_attr ruleset_attr = {
>> .handled_access_fs = access_fs_rw,
>> + .handled_access_net = access_net_tcp,
>> };
>>
>> if (argc < 2) {
>> fprintf(stderr,
>> - "usage: %s=\"...\" %s=\"...\" %s <cmd> [args]...\n\n",
>> - ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
>> + "usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\"%s "
>> + "<cmd> [args]...\n\n", ENV_FS_RO_NAME, ENV_FS_RW_NAME,
>> + ENV_TCP_BIND_NAME, ENV_TCP_CONNECT_NAME, argv[0]);
>> 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);
>> @@ -193,11 +257,19 @@ int main(const int argc, char *const argv[],
>> char *const *const envp)
>> "* %s: list of paths allowed to be used in a read-write
>> way.\n",
>> ENV_FS_RW_NAME);
>> fprintf(stderr,
>> - "\nexample:\n"
>> + "* %s: list of ports allowed to bind (server).\n",
>> + ENV_TCP_BIND_NAME);
>> + fprintf(stderr,
>> + "* %s: list of ports allowed to connect (client).\n",
>> + ENV_TCP_CONNECT_NAME);
>
> This is good and will be better with clang-format. ;)
Yep. I will fix it. Thanks.
>
>> + fprintf(stderr, "\nexample:\n"
>> "%s=\"/bin:/lib:/usr:/proc:/etc:/dev/urandom\" "
>> "%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
>> + "%s=\"15000:16000\" "
>
> Bind ports example should reference unprivileged ports such as "9418"
> (git, not well-known but OK).
>
Ok. I will change it
>
>> + "%s=\"10000:12000\" "
>
> Connect ports example should reference well-known ports such as "80:443".
>
Ditto.
>> "%s bash -i\n",
>> - ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
>> + ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
>> + ENV_TCP_CONNECT_NAME, argv[0]);
>> return 1;
>> }
>>
>> @@ -234,16 +306,25 @@ int main(const int argc, char *const argv[],
>> char *const *const envp)
>>
>> ruleset_fd =
>> landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr),
>> 0);
>> +
>
> Why?
Oh. Sorry. My mistake. I will fix it as it was.
>
>
>> if (ruleset_fd < 0) {
>> perror("Failed to create a ruleset");
>> return 1;
>> }
>> - if (populate_ruleset(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) {
>> + if (populate_ruleset_fs(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro))
>> goto err_close_ruleset;
>> - }
>
> Why? I know that checkpatch.pl prints a warning for that but I
> delibirately chooe to use curly braces even for "if" statements with one
> line because it is safer. This code may be copied/pasted and I'd like
> others to avoid introducing goto-fail-like issues.
>
It was done just to reduce the number of checkpatch.pl warnings.
If you want it to be formated in your way I will fix it.
>
>
>> - if (populate_ruleset(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) {
>> +
>> + if (populate_ruleset_fs(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw))
>> goto err_close_ruleset;
>> - }
>> +
>> + if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd,
>> + LANDLOCK_ACCESS_NET_BIND_TCP))
>
> So please use curly braces here too.
Ok. No problems.
>
>> + goto err_close_ruleset;
>> +
>> + if (populate_ruleset_net(ENV_TCP_CONNECT_NAME, ruleset_fd,
>> + LANDLOCK_ACCESS_NET_CONNECT_TCP))
>> + goto err_close_ruleset;
>> +
>> if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
>> perror("Failed to restrict privileges");
>> goto err_close_ruleset;
>> diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
>> index 916b30b31c06..e1ff40f238a6 100644
>> --- a/security/landlock/ruleset.h
>> +++ b/security/landlock/ruleset.h
>> @@ -19,7 +19,7 @@
>> #include "limits.h"
>> #include "object.h"
>>
>> -typedef u16 access_mask_t;
>> +typedef u32 access_mask_t;
>
> What‽
You are right. I will move this changes to another commit, related
the kernel updates. I might have forgotten to rebase this change and
left it in sandboxer patch. Thank you..
>
>
>>
>> /* Makes sure all filesystem access rights can be stored. */
>> static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS);
>> @@ -157,7 +157,7 @@ struct landlock_ruleset {
>> * layers are set once and never changed for the
>> * lifetime of the ruleset.
>> */
>> - u32 access_masks[];
>> + access_mask_t access_masks[];
>> };
>> };
>> };
>> --
>> 2.25.1
>>
> .
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