Re: [PATCH v10 09/13] landlock: Add network rules and TCP hooks support

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On 05/04/2023 19:42, Konstantin Meskhidze (A) wrote:


4/4/2023 7:42 PM, Mickaël Salaün пишет:

On 04/04/2023 11:31, Konstantin Meskhidze (A) wrote:


3/31/2023 8:24 PM, Mickaël Salaün пишет:

On 23/03/2023 09:52, Konstantin Meskhidze wrote:
This commit adds network rules support in the ruleset management
helpers and the landlock_create_ruleset syscall.
Refactor user space API to support network actions. Add new network
access flags, network rule and network attributes. Increment Landlock
ABI version. Expand access_masks_t to u32 to be sure network access
rights can be stored. Implement socket_bind() and socket_connect()
LSM hooks, which enable to restrict TCP socket binding and connection
to specific ports.

Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@xxxxxxxxxx>
---

Changes since v9:
* Changes UAPI port field to __u64.
* Moves shared code into check_socket_access().
* Adds get_raw_handled_net_accesses() and
get_current_net_domain() helpers.
* Minor fixes.

Changes since v8:
* Squashes commits.
* Refactors commit message.
* Changes UAPI port field to __be16.
* Changes logic of bind/connect hooks with AF_UNSPEC families.
* Adds address length checking.
* Minor fixes.

Changes since v7:
* Squashes commits.
* Increments ABI version to 4.
* Refactors commit message.
* Minor fixes.

Changes since v6:
* Renames landlock_set_net_access_mask() to landlock_add_net_access_mask()
     because it OR values.
* Makes landlock_add_net_access_mask() more resilient incorrect values.
* Refactors landlock_get_net_access_mask().
* Renames LANDLOCK_MASK_SHIFT_NET to LANDLOCK_SHIFT_ACCESS_NET and use
     LANDLOCK_NUM_ACCESS_FS as value.
* Updates access_masks_t to u32 to support network access actions.
* Refactors landlock internal functions to support network actions with
     landlock_key/key_type/id types.

Changes since v5:
* Gets rid of partial revert from landlock_add_rule
syscall.
* Formats code with clang-format-14.

Changes since v4:
* Refactors landlock_create_ruleset() - splits ruleset and
masks checks.
* Refactors landlock_create_ruleset() and landlock mask
setters/getters to support two rule types.
* Refactors landlock_add_rule syscall add_rule_path_beneath
function by factoring out get_ruleset_from_fd() and
landlock_put_ruleset().

Changes since v3:
* Splits commit.
* Adds network rule support for internal landlock functions.
* Adds set_mask and get_mask for network.
* Adds rb_root root_net_port.

---
    include/uapi/linux/landlock.h                |  49 +++++
    security/landlock/Kconfig                    |   1 +
    security/landlock/Makefile                   |   2 +
    security/landlock/limits.h                   |   6 +-
    security/landlock/net.c                      | 198 +++++++++++++++++++
    security/landlock/net.h                      |  26 +++
    security/landlock/ruleset.c                  |  52 ++++-
    security/landlock/ruleset.h                  |  63 +++++-
    security/landlock/setup.c                    |   2 +
    security/landlock/syscalls.c                 |  72 ++++++-
    tools/testing/selftests/landlock/base_test.c |   2 +-
    11 files changed, 450 insertions(+), 23 deletions(-)
    create mode 100644 security/landlock/net.c
    create mode 100644 security/landlock/net.h

[...]

diff --git a/security/landlock/net.c b/security/landlock/net.c

[...]

+static int check_addrlen(const struct sockaddr *const address, int addrlen)

const int addrlen

     Got it.

+{
+	if (addrlen < offsetofend(struct sockaddr, sa_family))
+		return -EINVAL;
+	switch (address->sa_family) {
+	case AF_UNSPEC:
+	case AF_INET:
+		if (addrlen < sizeof(struct sockaddr_in))
+			return -EINVAL;
+		return 0;
+#if IS_ENABLED(CONFIG_IPV6)
+	case AF_INET6:
+		if (addrlen < SIN6_LEN_RFC2133)
+			return -EINVAL;
+		return 0;
+#endif
+	}
+	WARN_ON_ONCE(1);
+	return 0;
+}
+
+static u16 get_port(const struct sockaddr *const address)
+{
+	/* Gets port value in host byte order. */
+	switch (address->sa_family) {
+	case AF_UNSPEC:
+	case AF_INET: {
+		const struct sockaddr_in *const sockaddr =
+			(struct sockaddr_in *)address;
+		return ntohs(sockaddr->sin_port);

Storing ports in big endian (in rulesets) would avoid converting them
every time the kernel checks a socket port. The above comment should
then be updated too.

     I thought we came to a conclusion to stick to host endianess and
let kernel do the checks under the hood:
https://lore.kernel.org/linux-security-module/278ab07f-7583-a4e0-3d37-1bacd091531d@xxxxxxxxxxx/

Did I misunderstand something?

We indeed stick to the host endianess for the UAPI/syscalls, but
internally the kernel has to do the conversion with as it is currently
done by calling ntohs(). To avoid calling ntohs() every time get_port()
is called, we can instead only call htons() when creating rules (i.e.
one-time htons call instead of multiple ntohs calls).

   Do you mean we need to covert port in  landlock_append_net_rule():

   ...

          int err;
	const struct landlock_id id = {
		.key.data = ntohs(port),
		.type = LANDLOCK_KEY_NET_PORT,
	};
	BUILD_BUG_ON(sizeof(port) > sizeof(id.key.data));
...
????

landlock_append_net_rule() takes a u16 (host endianess, which is the case with this patch series) and should store a big endian 16-bit integer. See my patch:

        const struct landlock_id id = {
-               .key.data = port,
+               .key.data = (__force uintptr_t)htons(port),
                .type = LANDLOCK_KEY_NET_PORT,
        };




    Do you mean we need to do port converting __be16 -> u16 in
check_socket_access()???

Removing the ntohs() call from get_port() enables to return __be16
instead of u16, and check_socket_access() will then need to use the same
type.

    Ok. I got it. Thanks.




+	}
+#if IS_ENABLED(CONFIG_IPV6)
+	case AF_INET6: {
+		const struct sockaddr_in6 *const sockaddr_ip6 =
+			(struct sockaddr_in6 *)address;
+		return ntohs(sockaddr_ip6->sin6_port);
+	}
+#endif
+	}
+	WARN_ON_ONCE(1);
+	return 0;
+}
+
+static int check_socket_access(struct socket *sock, struct sockaddr *address, int addrlen, u16 port,
+			       access_mask_t access_request)
+{
+	int ret;
+	bool allowed = false;
+	layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_NET] = {};
+	const struct landlock_rule *rule;
+	access_mask_t handled_access;
+	const struct landlock_id id = {
+		.key.data = port,
+		.type = LANDLOCK_KEY_NET_PORT,
+	};
+	const struct landlock_ruleset *const domain = get_current_net_domain();
+
+	if (WARN_ON_ONCE(!domain))
+		return 0;
+	if (WARN_ON_ONCE(domain->num_layers < 1))
+		return -EACCES;
+	/* Check if it's a TCP socket. */
+	if (sock->type != SOCK_STREAM)
+		return 0;
+
+	ret = check_addrlen(address, addrlen);
+	if (ret)
+		return ret;
+
+	switch (address->sa_family) {
+	case AF_UNSPEC:
+		/*
+		 * Connecting to an address with AF_UNSPEC dissolves the TCP
+		 * association, which have the same effect as closing the
+		 * connection while retaining the socket object (i.e., the file
+		 * descriptor).  As for dropping privileges, closing
+		 * connections is always allowed.
+		 */
+		if (access_request == LANDLOCK_ACCESS_NET_CONNECT_TCP)
+			return 0;
+
+		/*
+		 * For compatibility reason, accept AF_UNSPEC for bind
+		 * accesses (mapped to AF_INET) only if the address is
+		 * INADDR_ANY (cf. __inet_bind).  Checking the address is
+		 * required to not wrongfully return -EACCES instead of
+		 * -EAFNOSUPPORT.
+		 */
+		if (access_request == LANDLOCK_ACCESS_NET_BIND_TCP) {
+			const struct sockaddr_in *const sockaddr =
+				(struct sockaddr_in *)address;
+
+			if (sockaddr->sin_addr.s_addr != htonl(INADDR_ANY))
+				return -EAFNOSUPPORT;
+		}
+
+		fallthrough;
+	case AF_INET:
+#if IS_ENABLED(CONFIG_IPV6)
+	case AF_INET6:
+#endif
+		rule = landlock_find_rule(domain, id);
+		handled_access = landlock_init_layer_masks(
+			domain, access_request, &layer_masks,
+			LANDLOCK_KEY_NET_PORT);
+		allowed = landlock_unmask_layers(rule, handled_access,
+						 &layer_masks,
+						 ARRAY_SIZE(layer_masks));
+	}
+	return allowed ? 0 : -EACCES;
+}
+
+static int hook_socket_bind(struct socket *sock, struct sockaddr *address,
+			    int addrlen)
+{ >>> +	return check_socket_access(sock, address, addrlen, get_port(address),
+				   LANDLOCK_ACCESS_NET_BIND_TCP);

get_port() is called before check_addrlen(), which is an issue.

You'll find attached a patch for these fixes, please squash it in this
one for the next version.

I'll send other reviews by the end of the week.


+}
+
+static int hook_socket_connect(struct socket *sock, struct sockaddr *address,
+			       int addrlen)
+{
+	return check_socket_access(sock, address, addrlen, get_port(address),
+				   LANDLOCK_ACCESS_NET_CONNECT_TCP);
+}

[...]
.



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