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

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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 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.




+	}
+#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);
+}

[...]
.
From d6e53ea318ddfa32e54532f447412911709a80e1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= <mic@xxxxxxxxxxx>
Date: Tue, 4 Apr 2023 17:28:34 +0200
Subject: [PATCH] PATCH: Fix multiple issues in net.c

- Store ports in rulesets as __be16 to avoid runtime conversions.
- Constify arguments.
- Check address's length before dereferencing address to read the port.
- Fix and add comments.
- Format with clang-format.
---
 security/landlock/net.c | 55 ++++++++++++++++++++++++++---------------
 1 file changed, 35 insertions(+), 20 deletions(-)

diff --git a/security/landlock/net.c b/security/landlock/net.c
index e19c339906e7..663eee5920d5 100644
--- a/security/landlock/net.c
+++ b/security/landlock/net.c
@@ -22,9 +22,10 @@ int landlock_append_net_rule(struct landlock_ruleset *const ruleset,
 {
 	int err;
 	const struct landlock_id id = {
-		.key.data = port,
+		.key.data = (__force uintptr_t)htons(port),
 		.type = LANDLOCK_KEY_NET_PORT,
 	};
+
 	BUILD_BUG_ON(sizeof(port) > sizeof(id.key.data));
 
 	/* Transforms relative access rights to absolute ones. */
@@ -60,20 +61,24 @@ static const struct landlock_ruleset *get_current_net_domain(void)
 	return dom;
 }
 
-static int check_addrlen(const struct sockaddr *const address, int addrlen)
+static int check_addrlen(const struct sockaddr *const address,
+			 const int addrlen)
 {
 	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
 	}
@@ -81,7 +86,7 @@ static int check_addrlen(const struct sockaddr *const address, int addrlen)
 	return 0;
 }
 
-static u16 get_port(const struct sockaddr *const address)
+static __be16 get_port(const struct sockaddr *const address)
 {
 	/* Gets port value in host byte order. */
 	switch (address->sa_family) {
@@ -89,13 +94,13 @@ static u16 get_port(const struct sockaddr *const address)
 	case AF_INET: {
 		const struct sockaddr_in *const sockaddr =
 			(struct sockaddr_in *)address;
-		return ntohs(sockaddr->sin_port);
+		return sockaddr->sin_port;
 	}
 #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);
+		return sockaddr_ip6->sin6_port;
 	}
 #endif
 	}
@@ -103,16 +108,18 @@ static u16 get_port(const struct sockaddr *const address)
 	return 0;
 }
 
-static int check_socket_access(struct socket *sock, struct sockaddr *address, int addrlen, u16 port,
-			       access_mask_t access_request)
+static int check_socket_access(struct socket *const sock,
+			       struct sockaddr *const address,
+			       const int addrlen,
+			       const access_mask_t access_request)
 {
-	int ret;
+	int err;
+	__be16 port;
 	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,
+	struct landlock_id id = {
 		.type = LANDLOCK_KEY_NET_PORT,
 	};
 	const struct landlock_ruleset *const domain = get_current_net_domain();
@@ -121,13 +128,20 @@ static int check_socket_access(struct socket *sock, struct sockaddr *address, in
 		return 0;
 	if (WARN_ON_ONCE(domain->num_layers < 1))
 		return -EACCES;
-	/* Check if it's a TCP socket. */
+
+	/* Checks if it's a TCP socket. */
 	if (sock->type != SOCK_STREAM)
 		return 0;
 
-	ret = check_addrlen(address, addrlen);
-	if (ret)
-		return ret;
+	/* Checks for minimal header length. */
+	err = check_addrlen(address, addrlen);
+	if (err)
+		return err;
+
+	/* It is now safe to read the port. */
+	port = get_port(address);
+	id.key.data = (__force uintptr_t)port;
+	BUILD_BUG_ON(sizeof(port) > sizeof(id.key.data));
 
 	switch (address->sa_family) {
 	case AF_UNSPEC:
@@ -172,17 +186,18 @@ static int check_socket_access(struct socket *sock, struct sockaddr *address, in
 	return allowed ? 0 : -EACCES;
 }
 
-static int hook_socket_bind(struct socket *sock, struct sockaddr *address,
-			    int addrlen)
+static int hook_socket_bind(struct socket *const sock,
+			    struct sockaddr *const address, const int addrlen)
 {
-	return check_socket_access(sock, address, addrlen, get_port(address),
+	return check_socket_access(sock, address, addrlen,
 				   LANDLOCK_ACCESS_NET_BIND_TCP);
 }
 
-static int hook_socket_connect(struct socket *sock, struct sockaddr *address,
-			       int addrlen)
+static int hook_socket_connect(struct socket *const sock,
+			       struct sockaddr *const address,
+			       const int addrlen)
 {
-	return check_socket_access(sock, address, addrlen, get_port(address),
+	return check_socket_access(sock, address, addrlen,
 				   LANDLOCK_ACCESS_NET_CONNECT_TCP);
 }
 
-- 
2.39.0


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