On 21/10/2022 17:26, Konstantin Meskhidze wrote:
This patch adds support of socket_bind() and socket_connect() hooks.
It's possible to restrict binding and connecting of TCP sockets to
particular ports.
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 v7:
* Minor fixes.
* Refactors commit message.
Changes since v6:
* Updates copyright.
* Refactors landlock_append_net_rule() and check_socket_access()
functions with landlock_id type.
Changes since v5:
* Fixes some logic errors.
* Formats code with clang-format-14.
Changes since v4:
* Factors out CONFIG_INET into make file.
* Refactors check_socket_access().
* Adds helper get_port().
* Adds CONFIG_IPV6 in get_port(), hook_socket_bind/connect
functions to support AF_INET6 family.
* Adds AF_UNSPEC family support in hook_socket_bind/connect
functions.
* Refactors add_rule_net_service() and landlock_add_rule
syscall to support network rule inserting.
* Refactors init_layer_masks() to support network rules.
Changes since v3:
* Splits commit.
* Adds SECURITY_NETWORK in config.
* Adds IS_ENABLED(CONFIG_INET) if a kernel has no INET configuration.
* Adds hook_socket_bind and hook_socket_connect hooks.
---
security/landlock/Kconfig | 1 +
security/landlock/Makefile | 2 +
security/landlock/net.c | 164 +++++++++++++++++++++++++++++++++++
security/landlock/net.h | 26 ++++++
security/landlock/setup.c | 2 +
security/landlock/syscalls.c | 59 ++++++++++++-
6 files changed, 251 insertions(+), 3 deletions(-)
create mode 100644 security/landlock/net.c
create mode 100644 security/landlock/net.h
diff --git a/security/landlock/Kconfig b/security/landlock/Kconfig
index 8e33c4e8ffb8..10c099097533 100644
--- a/security/landlock/Kconfig
+++ b/security/landlock/Kconfig
@@ -3,6 +3,7 @@
config SECURITY_LANDLOCK
bool "Landlock support"
depends on SECURITY && !ARCH_EPHEMERAL_INODES
+ select SECURITY_NETWORK
select SECURITY_PATH
help
Landlock is a sandboxing mechanism that enables processes to restrict
diff --git a/security/landlock/Makefile b/security/landlock/Makefile
index 7bbd2f413b3e..53d3c92ae22e 100644
--- a/security/landlock/Makefile
+++ b/security/landlock/Makefile
@@ -2,3 +2,5 @@ obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
landlock-y := setup.o syscalls.o object.o ruleset.o \
cred.o ptrace.o fs.o
+
+landlock-$(CONFIG_INET) += net.o
\ No newline at end of file
diff --git a/security/landlock/net.c b/security/landlock/net.c
new file mode 100644
index 000000000000..39e8a156a1f4
--- /dev/null
+++ b/security/landlock/net.c
@@ -0,0 +1,164 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - Network management and hooks
+ *
+ * Copyright © 2022 Huawei Tech. Co., Ltd.
+ * Copyright © 2022 Microsoft Corporation
+ */
+
+#include <linux/in.h>
+#include <linux/net.h>
+#include <linux/socket.h>
+#include <net/ipv6.h>
+
+#include "common.h"
+#include "cred.h"
+#include "limits.h"
+#include "net.h"
+#include "ruleset.h"
+
+int landlock_append_net_rule(struct landlock_ruleset *const ruleset,
+ const u16 port, access_mask_t access_rights)
+{
+ int err;
+ const struct landlock_id id = {
+ .key.data = port,
+ .type = LANDLOCK_KEY_NET_PORT,
+ };
+ BUILD_BUG_ON(sizeof(port) > sizeof(id.key.data));
+
+ /* Transforms relative access rights to absolute ones. */
+ access_rights |= LANDLOCK_MASK_ACCESS_NET &
+ ~landlock_get_net_access_mask(ruleset, 0);
+
+ mutex_lock(&ruleset->lock);
+ err = landlock_insert_rule(ruleset, id, access_rights);
+ mutex_unlock(&ruleset->lock);
+
+ return err;
+}
+
+static int check_socket_access(const struct landlock_ruleset *const domain,
+ u16 port, access_mask_t access_request)
+{
+ 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,
+ };
+
+ if (WARN_ON_ONCE(!domain))
+ return 0;
+ if (WARN_ON_ONCE(domain->num_layers < 1))
+ return -EACCES;
+
+ rule = landlock_find_rule(domain, id);
+ handled_access = init_layer_masks(domain, access_request, &layer_masks,
+ LANDLOCK_KEY_NET_PORT);
+ allowed = unmask_layers(rule, handled_access, &layer_masks,
+ ARRAY_SIZE(layer_masks));
+
+ return allowed ? 0 : -EACCES;
+}
+
+static u16 get_port(const struct sockaddr *const address)
get_port() should return a __be16 type. This enables to avoid converting
port when checking a rule.
make C=2 security/landlock/ must not print any warning.
+{
+ /* 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);
+ }
+#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 hook_socket_bind(struct socket *sock, struct sockaddr *address,
+ int addrlen)
+{
+ const struct landlock_ruleset *const dom =
+ landlock_get_current_domain();
+
+ if (!dom)
+ return 0;
+
+ /* Check if it's a TCP socket. */
+ if (sock->type != SOCK_STREAM)
+ return 0;
+
+ switch (address->sa_family) {
+ case AF_UNSPEC:
+ case AF_INET:
+#if IS_ENABLED(CONFIG_IPV6)
+ case AF_INET6:
+#endif
+ return check_socket_access(dom, get_port(address),
+ LANDLOCK_ACCESS_NET_BIND_TCP);
+ default:
+ return 0;
You can remove this default case and move the return 0 at the end of the
function.
+ }
+}
+
+static int hook_socket_connect(struct socket *sock, struct sockaddr *address,
+ int addrlen)
+{
+ const struct landlock_ruleset *const dom =
+ landlock_get_current_domain();
+
+ if (!dom)
+ return 0;
+
+ /* Check if it's a TCP socket. */
+ if (sock->type != SOCK_STREAM)
+ return 0;
+
+ /* Check if the hook is AF_INET* socket's action. */
+ switch (address->sa_family) {
+ case AF_INET:
+#if IS_ENABLED(CONFIG_IPV6)
+ case AF_INET6:
+#endif
+ return check_socket_access(dom, get_port(address),
+ LANDLOCK_ACCESS_NET_CONNECT_TCP);
+ case AF_UNSPEC: {
+ u16 i;
You can move "i" after the "dom" declaration to remove the extra braces.
+
+ /*
+ * If just in a layer a mask supports connect access,
+ * the socket_connect() hook with AF_UNSPEC family flag
+ * must be banned. This prevents from disconnecting already
+ * connected sockets.
+ */
+ for (i = 0; i < dom->num_layers; i++) {
+ if (landlock_get_net_access_mask(dom, i) &
+ LANDLOCK_ACCESS_NET_CONNECT_TCP)
+ return -EACCES;
I'm wondering if this is the right error code for this case. EPERM may
be more appropriate.
Thinking more about this case, I don't understand what is the rationale
to deny such action. What would be the consequence to always allow
connection with AF_UNSPEC (i.e. to disconnect a socket)?
+ }
+ }
+ }
+ return 0;
+}
+
+static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
+ LSM_HOOK_INIT(socket_bind, hook_socket_bind),
+ LSM_HOOK_INIT(socket_connect, hook_socket_connect),
+};
+
+__init void landlock_add_net_hooks(void)
+{
+ security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
+ LANDLOCK_NAME);
+}
diff --git a/security/landlock/net.h b/security/landlock/net.h
new file mode 100644
index 000000000000..0da1d9dff5ab
--- /dev/null
+++ b/security/landlock/net.h
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock LSM - Network management and hooks
+ *
+ * Copyright © 2022 Huawei Tech. Co., Ltd.
+ */
+
+#ifndef _SECURITY_LANDLOCK_NET_H
+#define _SECURITY_LANDLOCK_NET_H
+
+#include "common.h"
+#include "ruleset.h"
+#include "setup.h"
+
+#if IS_ENABLED(CONFIG_INET)
+__init void landlock_add_net_hooks(void);
+
+int landlock_append_net_rule(struct landlock_ruleset *const ruleset,
+ const u16 port, access_mask_t access_rights);
+#else /* IS_ENABLED(CONFIG_INET) */
+static inline void landlock_add_net_hooks(void)
+{
+}
+#endif /* IS_ENABLED(CONFIG_INET) */
+
+#endif /* _SECURITY_LANDLOCK_NET_H */
diff --git a/security/landlock/setup.c b/security/landlock/setup.c
index 3f196d2ce4f9..7e4a598177b8 100644
--- a/security/landlock/setup.c
+++ b/security/landlock/setup.c
@@ -14,6 +14,7 @@
#include "fs.h"
#include "ptrace.h"
#include "setup.h"
+#include "net.h"
bool landlock_initialized __lsm_ro_after_init = false;
@@ -29,6 +30,7 @@ static int __init landlock_init(void)
landlock_add_cred_hooks();
landlock_add_ptrace_hooks();
landlock_add_fs_hooks();
+ landlock_add_net_hooks();
landlock_initialized = true;
pr_info("Up and running.\n");
return 0;
diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
index c5a6ad4e2fca..7853f32e8325 100644
--- a/security/landlock/syscalls.c
+++ b/security/landlock/syscalls.c
@@ -29,6 +29,7 @@
#include "cred.h"
#include "fs.h"
#include "limits.h"
+#include "net.h"
#include "ruleset.h"
#include "setup.h"
@@ -74,7 +75,8 @@ static void build_check_abi(void)
{
struct landlock_ruleset_attr ruleset_attr;
struct landlock_path_beneath_attr path_beneath_attr;
- size_t ruleset_size, path_beneath_size;
+ struct landlock_net_service_attr net_service_attr;
+ size_t ruleset_size, path_beneath_size, net_service_size;
/*
* For each user space ABI structures, first checks that there is no
@@ -90,6 +92,11 @@ static void build_check_abi(void)
path_beneath_size += sizeof(path_beneath_attr.parent_fd);
BUILD_BUG_ON(sizeof(path_beneath_attr) != path_beneath_size);
BUILD_BUG_ON(sizeof(path_beneath_attr) != 12);
+
+ net_service_size = sizeof(net_service_attr.allowed_access);
+ net_service_size += sizeof(net_service_attr.port);
+ BUILD_BUG_ON(sizeof(net_service_attr) != net_service_size);
+ BUILD_BUG_ON(sizeof(net_service_attr) != 10);
}
/* Ruleset handling */
@@ -322,13 +329,54 @@ static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
return err;
}
+static int add_rule_net_service(struct landlock_ruleset *ruleset,
+ const void __user *const rule_attr)
+{
+#if IS_ENABLED(CONFIG_INET)
+ struct landlock_net_service_attr net_service_attr;
+ int res;
+ u32 mask;
access_mask_t mask;
+
+ /* Copies raw user space buffer, only one type for now. */
+ res = copy_from_user(&net_service_attr, rule_attr,
+ sizeof(net_service_attr));
+ if (res)
+ return -EFAULT;
+
+ /*
+ * Informs about useless rule: empty allowed_access (i.e. deny rules)
+ * are ignored by network actions.
+ */
+ if (!net_service_attr.allowed_access)
+ return -ENOMSG;
+
+ /*
+ * Checks that allowed_access matches the @ruleset constraints
+ * (ruleset->access_masks[0] is automatically upgraded to 64-bits).
+ */
+ mask = landlock_get_net_access_mask(ruleset, 0);
+ if ((net_service_attr.allowed_access | mask) != mask)
+ return -EINVAL;
+
+ /* Denies inserting a rule with port 0. */
+ if (net_service_attr.port == 0)
+ return -EINVAL;
+
+ /* Imports the new rule. */
+ return landlock_append_net_rule(ruleset, net_service_attr.port,
+ net_service_attr.allowed_access);
+#else /* IS_ENABLED(CONFIG_INET) */
+ return -EAFNOSUPPORT;
+#endif /* IS_ENABLED(CONFIG_INET) */
+}
+
/**
* sys_landlock_add_rule - Add a new rule to a ruleset
*
* @ruleset_fd: File descriptor tied to the ruleset that should be extended
* with the new rule.
- * @rule_type: Identify the structure type pointed to by @rule_attr (only
- * %LANDLOCK_RULE_PATH_BENEATH for now).
+ * @rule_type: Identify the structure type pointed to by @rule_attr:
+ * %LANDLOCK_RULE_PATH_BENEATH or %LANDLOCK_RULE_NET_SERVICE.
* @rule_attr: Pointer to a rule (only of type &struct
* landlock_path_beneath_attr for now).
* @flags: Must be 0.
@@ -339,6 +387,8 @@ static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
* Possible returned errors are:
*
* - %EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
+ * - %EAFNOSUPPORT: @rule_type is LANDLOCK_RULE_NET_SERVICE but TCP/IP is not
%LANDLOCK_RULE_NET_SERVICE
+ * supported by the running kernel;
* - %EINVAL: @flags is not 0, or inconsistent access in the rule (i.e.
* &landlock_path_beneath_attr.allowed_access is not a subset of the
* ruleset handled accesses);
@@ -373,6 +423,9 @@ SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
case LANDLOCK_RULE_PATH_BENEATH:
err = add_rule_path_beneath(ruleset, rule_attr);
break;
+ case LANDLOCK_RULE_NET_SERVICE:
+ err = add_rule_net_service(ruleset, rule_attr);
+ break;
default:
err = -EINVAL;
break;
--
2.25.1
.
