[PATCH v3] landlock: Add abstract unix socket connect restriction
Tahera Fahimi
fahimitahera at gmail.com
Thu Jun 6 04:36:11 UTC 2024
Abstract unix sockets are used for local inter-process communications
without on a filesystem. Currently a sandboxed process can connect to a
socket outside of the sandboxed environment, since landlock has no
restriction for connecting to a unix socket in the abstract namespace.
Access to such sockets for a sandboxed process should be scoped the same
way ptrace is limited.
Because of compatibility reasons and since landlock should be flexible,
we extend the user space interface by adding a new "scoped" field. This
field optionally contains a "LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET" to
specify that the ruleset will deny any connection from within the
sandbox to its parents(i.e. any parent sandbox or non-sandbox processes)
Closes: https://github.com/landlock-lsm/linux/issues/7
Signed-off-by: Tahera Fahimi <fahimitahera at gmail.com>
-------
V3: Added "scoped" field to landlock_ruleset_attr
V2: Remove wrapper functions
-------
---
include/uapi/linux/landlock.h | 22 +++++++++++++++
security/landlock/limits.h | 5 ++++
security/landlock/ruleset.c | 16 +++++++----
security/landlock/ruleset.h | 31 ++++++++++++++++++--
security/landlock/syscalls.c | 9 ++++--
security/landlock/task.c | 53 ++++++++++++++++++-----------------
6 files changed, 102 insertions(+), 34 deletions(-)
diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
index 68625e728f43..1641aeb9eeaa 100644
--- a/include/uapi/linux/landlock.h
+++ b/include/uapi/linux/landlock.h
@@ -37,6 +37,12 @@ struct landlock_ruleset_attr {
* rule explicitly allow them.
*/
__u64 handled_access_net;
+ /**
+ * scoped: Bitmask of actions (cf. `Scope access flags`_)
+ * that is handled by this ruleset and should be permitted
+ * by default if no rule explicitly deny them.
+ */
+ __u64 scoped;
};
/*
@@ -266,4 +272,20 @@ struct landlock_net_port_attr {
#define LANDLOCK_ACCESS_NET_BIND_TCP (1ULL << 0)
#define LANDLOCK_ACCESS_NET_CONNECT_TCP (1ULL << 1)
/* clang-format on */
+
+/**
+ * DOC: scoped
+ *
+ * Scope access flags
+ * ~~~~~~~~~~~~~~~~~~~~
+ * These flags enable to restrict a sandboxed process to a set of
+ * inter-process communications actions.
+ *
+ * IPCs with scoped actions:
+ * - %LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET: Restrict a sandbox process to
+ * connect to another process through abstract unix sockets.
+ */
+/* clang-format off */
+#define LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET (1ULL << 0)
+/* clang-format on*/
#endif /* _UAPI_LINUX_LANDLOCK_H */
diff --git a/security/landlock/limits.h b/security/landlock/limits.h
index 20fdb5ff3514..d6fb82fd1e67 100644
--- a/security/landlock/limits.h
+++ b/security/landlock/limits.h
@@ -28,6 +28,11 @@
#define LANDLOCK_NUM_ACCESS_NET __const_hweight64(LANDLOCK_MASK_ACCESS_NET)
#define LANDLOCK_SHIFT_ACCESS_NET LANDLOCK_NUM_ACCESS_FS
+#define LANDLOCK_LAST_ACCESS_UNIX LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET
+#define LANDLOCK_MASK_ACCESS_UNIX ((LANDLOCK_LAST_ACCESS_UNIX << 1) - 1)
+#define LANDLOCK_NUM_ACCESS_UNIX __const_hweight64(LANDLOCK_MASK_ACCESS_UNIX)
+#define LANDLOCK_SHIFT_ACCESS_UNIX LANDLOCK_SHIFT_ACCESS_NET
+
/* clang-format on */
#endif /* _SECURITY_LANDLOCK_LIMITS_H */
diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index e0a5fbf9201a..0592e53cdc9d 100644
--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c
@@ -52,12 +52,13 @@ static struct landlock_ruleset *create_ruleset(const u32 num_layers)
struct landlock_ruleset *
landlock_create_ruleset(const access_mask_t fs_access_mask,
- const access_mask_t net_access_mask)
+ const access_mask_t net_access_mask,
+ const access_mask_t unix_access_mask)
{
struct landlock_ruleset *new_ruleset;
/* Informs about useless ruleset. */
- if (!fs_access_mask && !net_access_mask)
+ if (!fs_access_mask && !net_access_mask && !unix_access_mask)
return ERR_PTR(-ENOMSG);
new_ruleset = create_ruleset(1);
if (IS_ERR(new_ruleset))
@@ -66,6 +67,9 @@ landlock_create_ruleset(const access_mask_t fs_access_mask,
landlock_add_fs_access_mask(new_ruleset, fs_access_mask, 0);
if (net_access_mask)
landlock_add_net_access_mask(new_ruleset, net_access_mask, 0);
+ if (unix_access_mask)
+ landlock_add_unix_socket_access_mask(new_ruleset,
+ unix_access_mask, 0);
return new_ruleset;
}
@@ -173,9 +177,11 @@ static void build_check_ruleset(void)
BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES);
BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS);
- BUILD_BUG_ON(access_masks <
- ((LANDLOCK_MASK_ACCESS_FS << LANDLOCK_SHIFT_ACCESS_FS) |
- (LANDLOCK_MASK_ACCESS_NET << LANDLOCK_SHIFT_ACCESS_NET)));
+ BUILD_BUG_ON(
+ access_masks <
+ ((LANDLOCK_MASK_ACCESS_FS << LANDLOCK_SHIFT_ACCESS_FS) |
+ (LANDLOCK_MASK_ACCESS_NET << LANDLOCK_SHIFT_ACCESS_NET) |
+ (LANDLOCK_MASK_ACCESS_UNIX << LANDLOCK_SHIFT_ACCESS_UNIX)));
}
/**
diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
index c7f1526784fd..6e755d924a5e 100644
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h
@@ -35,6 +35,8 @@ typedef u16 access_mask_t;
static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS);
/* Makes sure all network access rights can be stored. */
static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_NET);
+/* Makes sure all abstract Unix Socket access rights can be stored*/
+static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_UNIX);
/* Makes sure for_each_set_bit() and for_each_clear_bit() calls are OK. */
static_assert(sizeof(unsigned long) >= sizeof(access_mask_t));
@@ -42,7 +44,8 @@ static_assert(sizeof(unsigned long) >= sizeof(access_mask_t));
typedef u32 access_masks_t;
/* Makes sure all ruleset access rights can be stored. */
static_assert(BITS_PER_TYPE(access_masks_t) >=
- LANDLOCK_NUM_ACCESS_FS + LANDLOCK_NUM_ACCESS_NET);
+ LANDLOCK_NUM_ACCESS_FS + LANDLOCK_NUM_ACCESS_NET +
+ LANDLOCK_NUM_ACCESS_UNIX);
typedef u16 layer_mask_t;
/* Makes sure all layers can be checked. */
@@ -233,7 +236,8 @@ struct landlock_ruleset {
struct landlock_ruleset *
landlock_create_ruleset(const access_mask_t access_mask_fs,
- const access_mask_t access_mask_net);
+ const access_mask_t access_mask_net,
+ const access_mask_t access_mask_unix);
void landlock_put_ruleset(struct landlock_ruleset *const ruleset);
void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset);
@@ -282,6 +286,18 @@ landlock_add_net_access_mask(struct landlock_ruleset *const ruleset,
(net_mask << LANDLOCK_SHIFT_ACCESS_NET);
}
+static inline void
+landlock_add_unix_socket_access_mask(struct landlock_ruleset *const ruleset,
+ const access_mask_t unix_access_mask,
+ const u16 layer_level)
+{
+ access_mask_t unix_mask = unix_access_mask & LANDLOCK_MASK_ACCESS_UNIX;
+
+ WARN_ON_ONCE(unix_access_mask != unix_mask);
+ ruleset->access_masks[layer_level] |=
+ (unix_mask << LANDLOCK_SHIFT_ACCESS_UNIX);
+}
+
static inline access_mask_t
landlock_get_raw_fs_access_mask(const struct landlock_ruleset *const ruleset,
const u16 layer_level)
@@ -309,6 +325,17 @@ landlock_get_net_access_mask(const struct landlock_ruleset *const ruleset,
LANDLOCK_MASK_ACCESS_NET;
}
+static inline access_mask_t
+landlock_get_unix_access_mask(const struct landlock_ruleset *const ruleset,
+ const u16 layer_level)
+{
+ return landlock_get_raw_fs_access_mask(ruleset, layer_level) |
+ LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
+ return (ruleset->access_masks[layer_level] >>
+ LANDLOCK_SHIFT_ACCESS_UNIX) &
+ LANDLOCK_MASK_ACCESS_UNIX;
+}
+
bool landlock_unmask_layers(const struct landlock_rule *const rule,
const access_mask_t access_request,
layer_mask_t (*const layer_masks)[],
diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
index 03b470f5a85a..955d3d028963 100644
--- a/security/landlock/syscalls.c
+++ b/security/landlock/syscalls.c
@@ -97,8 +97,9 @@ static void build_check_abi(void)
*/
ruleset_size = sizeof(ruleset_attr.handled_access_fs);
ruleset_size += sizeof(ruleset_attr.handled_access_net);
+ ruleset_size += sizeof(ruleset_attr.scoped);
BUILD_BUG_ON(sizeof(ruleset_attr) != ruleset_size);
- BUILD_BUG_ON(sizeof(ruleset_attr) != 16);
+ BUILD_BUG_ON(sizeof(ruleset_attr) != 24);
path_beneath_size = sizeof(path_beneath_attr.allowed_access);
path_beneath_size += sizeof(path_beneath_attr.parent_fd);
@@ -212,10 +213,14 @@ SYSCALL_DEFINE3(landlock_create_ruleset,
if ((ruleset_attr.handled_access_net | LANDLOCK_MASK_ACCESS_NET) !=
LANDLOCK_MASK_ACCESS_NET)
return -EINVAL;
+ if ((ruleset_attr.scoped | LANDLOCK_MASK_ACCESS_UNIX) !=
+ LANDLOCK_MASK_ACCESS_UNIX)
+ return -EINVAL;
/* Checks arguments and transforms to kernel struct. */
ruleset = landlock_create_ruleset(ruleset_attr.handled_access_fs,
- ruleset_attr.handled_access_net);
+ ruleset_attr.handled_access_net,
+ ruleset_attr.scoped);
if (IS_ERR(ruleset))
return PTR_ERR(ruleset);
diff --git a/security/landlock/task.c b/security/landlock/task.c
index 67528f87b7de..b42f31cca2ae 100644
--- a/security/landlock/task.c
+++ b/security/landlock/task.c
@@ -14,6 +14,7 @@
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <net/sock.h>
+#include <net/af_unix.h>
#include "common.h"
#include "cred.h"
@@ -109,32 +110,25 @@ static int hook_ptrace_traceme(struct task_struct *const parent)
return task_ptrace(parent, current);
}
-static bool unix_sock_is_scoped(struct sock *const sock,
- struct sock *const other)
+static bool sock_is_scoped(struct sock *const sock, struct sock *const other)
{
bool is_scoped = true;
-
- /* get the ruleset of connecting sock*/
- const struct landlock_ruleset *const dom_sock =
- landlock_get_current_domain();
-
- if (!dom_sock)
- return true;
-
- /* get credential of listening sock*/
- const struct cred *cred_other = get_cred(other->sk_peer_cred);
-
- if (!cred_other)
- return true;
-
- /* retrieve the landlock_rulesets */
- const struct landlock_ruleset *dom_parent;
-
- rcu_read_lock();
- dom_parent = landlock_cred(cred_other)->domain;
- is_scoped = domain_scope_le(dom_parent, dom_sock);
- rcu_read_unlock();
-
+ const struct landlock_ruleset *dom_other;
+ const struct cred *cred_other;
+
+ const struct landlock_ruleset *const dom = landlock_get_current_domain();
+ if (!dom)
+ goto out_put_cred;
+
+
+ lockdep_assert_held(&unix_sk(other)->lock);
+ /* the credentials will not change */
+ cred_other = get_cred(other->sk_peer_cred);
+ dom_other = landlock_cred(cred_other)->domain;
+ is_scoped = domain_scope_le(dom, dom_other);
+
+out_put_cred:
+ put_cred(cred_other);
return is_scoped;
}
@@ -142,7 +136,15 @@ static int hook_unix_stream_connect(struct sock *const sock,
struct sock *const other,
struct sock *const newsk)
{
- if (unix_sock_is_scoped(sock, other))
+ if (sock_is_scoped(sock, other))
+ return 0;
+ return -EPERM;
+}
+
+static int hook_unix_may_send(struct socket *const sock,
+ struct socket *const other)
+{
+ if (sock_is_scoped(sock->sk, other->sk))
return 0;
return -EPERM;
}
@@ -151,6 +153,7 @@ static struct security_hook_list landlock_hooks[] __ro_after_init = {
LSM_HOOK_INIT(ptrace_access_check, hook_ptrace_access_check),
LSM_HOOK_INIT(ptrace_traceme, hook_ptrace_traceme),
LSM_HOOK_INIT(unix_stream_connect, hook_unix_stream_connect),
+ LSM_HOOK_INIT(unix_may_send, hook_unix_may_send),
};
__init void landlock_add_task_hooks(void)
--
2.34.1
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