[PATCH v6] landlock: Add abstract unix socket connect restriction
Tahera Fahimi
fahimitahera at gmail.com
Thu Jun 27 23:30:17 UTC 2024
Abstract unix sockets are used for local inter-process communications
without a filesystem. Currently a sandboxed process can connect to a
socket outside of the sandboxed environment, since Landlock has no
restriction for connecting to an abstract socket address. 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 to the
ruleset attribute structure. 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>
-------
v6: Removing tests. Removing curr_ruleset.
v5: Added curr_ruleset to hierarachy_ruleset structure for optional
scoping purpose.
V4: Added tests and changes in task.c to scope different sockets
differently.
V3: Added "scoped" field to landlock_ruleset_attr
V2: Remove wrapper functions
-------
Signed-off-by: Tahera Fahimi <fahimitahera at gmail.com>
---
include/uapi/linux/landlock.h | 29 ++++++++++++++++
security/landlock/limits.h | 3 ++
security/landlock/ruleset.c | 7 ++--
security/landlock/ruleset.h | 23 ++++++++++++-
security/landlock/syscalls.c | 12 +++++--
security/landlock/task.c | 62 +++++++++++++++++++++++++++++++++++
6 files changed, 130 insertions(+), 6 deletions(-)
diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
index 68625e728f43..010aaca5b05a 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 scopes (cf. `Scope flags`_)
+ * restricting a Landlock domain from accessing outside
+ * resources(e.g. IPCs).
+ */
+ __u64 scoped;
};
/*
@@ -266,4 +272,27 @@ 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: scope
+ *
+ * .scoped attribute handles a set of restrictions on kernel IPCs through
+ * the following flags.
+ *
+ * Scope flags
+ * ~~~~~~~~~~~
+ *
+ * These flags enable to restrict a sandboxed process from a set of IPC
+ * actions. Setting a flag for a ruleset will isolate the Landlock domain
+ * to forbid connections to resources outside the domain.
+ *
+ * IPCs with scoped actions:
+ * - %LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET: Restrict a sandboxed process
+ * from connecting to an abstract unix socket created by a process
+ * outside the related Landlock domain (e.g. a parent domain or a process
+ * which is not sandboxed).
+ */
+/* 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 4eb643077a2a..eb01d0fb2165 100644
--- a/security/landlock/limits.h
+++ b/security/landlock/limits.h
@@ -26,6 +26,9 @@
#define LANDLOCK_MASK_ACCESS_NET ((LANDLOCK_LAST_ACCESS_NET << 1) - 1)
#define LANDLOCK_NUM_ACCESS_NET __const_hweight64(LANDLOCK_MASK_ACCESS_NET)
+#define LANDLOCK_LAST_SCOPE LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET
+#define LANDLOCK_MASK_SCOPE ((LANDLOCK_LAST_SCOPE << 1) - 1)
+#define LANDLOCK_NUM_SCOPE __const_hweight64(LANDLOCK_MASK_SCOPE)
/* clang-format on */
#endif /* _SECURITY_LANDLOCK_LIMITS_H */
diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index 6ff232f58618..a93bdbf52fff 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 scope_mask)
{
struct landlock_ruleset *new_ruleset;
/* Informs about useless ruleset. */
- if (!fs_access_mask && !net_access_mask)
+ if (!fs_access_mask && !net_access_mask && !scope_mask)
return ERR_PTR(-ENOMSG);
new_ruleset = create_ruleset(1);
if (IS_ERR(new_ruleset))
@@ -66,6 +67,8 @@ 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 (scope_mask)
+ landlock_add_scope_mask(new_ruleset, scope_mask, 0);
return new_ruleset;
}
diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
index 0f1b5b4c8f6b..c749fa0b3ecd 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 scoped rights can be stored*/
+static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_SCOPE);
/* Makes sure for_each_set_bit() and for_each_clear_bit() calls are OK. */
static_assert(sizeof(unsigned long) >= sizeof(access_mask_t));
@@ -42,6 +44,7 @@ static_assert(sizeof(unsigned long) >= sizeof(access_mask_t));
struct access_masks {
access_mask_t fs : LANDLOCK_NUM_ACCESS_FS;
access_mask_t net : LANDLOCK_NUM_ACCESS_NET;
+ access_mask_t scoped : LANDLOCK_NUM_SCOPE;
};
typedef u16 layer_mask_t;
@@ -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 scope_mask);
void landlock_put_ruleset(struct landlock_ruleset *const ruleset);
void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset);
@@ -280,6 +284,16 @@ landlock_add_net_access_mask(struct landlock_ruleset *const ruleset,
ruleset->access_masks[layer_level].net |= net_mask;
}
+static inline void
+landlock_add_scope_mask(struct landlock_ruleset *const ruleset,
+ const access_mask_t scope_mask, const u16 layer_level)
+{
+ access_mask_t scoped_mask = scope_mask & LANDLOCK_MASK_SCOPE;
+
+ WARN_ON_ONCE(scope_mask != scoped_mask);
+ ruleset->access_masks[layer_level].scoped |= scoped_mask;
+}
+
static inline access_mask_t
landlock_get_raw_fs_access_mask(const struct landlock_ruleset *const ruleset,
const u16 layer_level)
@@ -303,6 +317,13 @@ landlock_get_net_access_mask(const struct landlock_ruleset *const ruleset,
return ruleset->access_masks[layer_level].net;
}
+static inline access_mask_t
+landlock_get_scope_mask(const struct landlock_ruleset *const ruleset,
+ const u16 layer_level)
+{
+ return ruleset->access_masks[layer_level].scoped;
+}
+
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..8ea0a13bee83 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);
@@ -170,7 +171,7 @@ static const struct file_operations ruleset_fops = {
* Possible returned errors are:
*
* - %EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
- * - %EINVAL: unknown @flags, or unknown access, or too small @size;
+ * - %EINVAL: unknown @flags, or unknown access, or uknown scope, or too small @size;
* - %E2BIG or %EFAULT: @attr or @size inconsistencies;
* - %ENOMSG: empty &landlock_ruleset_attr.handled_access_fs.
*/
@@ -213,9 +214,14 @@ SYSCALL_DEFINE3(landlock_create_ruleset,
LANDLOCK_MASK_ACCESS_NET)
return -EINVAL;
+ /* Checks IPC scoping content (and 32-bits cast). */
+ if ((ruleset_attr.scoped | LANDLOCK_MASK_SCOPE) != LANDLOCK_MASK_SCOPE)
+ 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 849f5123610b..acc6e0fbc111 100644
--- a/security/landlock/task.c
+++ b/security/landlock/task.c
@@ -13,6 +13,8 @@
#include <linux/lsm_hooks.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
+#include <net/sock.h>
+#include <net/af_unix.h>
#include "common.h"
#include "cred.h"
@@ -108,9 +110,69 @@ static int hook_ptrace_traceme(struct task_struct *const parent)
return task_ptrace(parent, current);
}
+static access_mask_t
+get_scoped_accesses(const struct landlock_ruleset *const domain)
+{
+ access_mask_t access_dom = 0;
+ size_t layer_level;
+
+ for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
+ access_dom |= landlock_get_scope_mask(domain, layer_level);
+ return access_dom;
+}
+
+static bool sock_is_scoped(struct sock *const other)
+{
+ const struct landlock_ruleset *dom_other;
+ const struct landlock_ruleset *const dom =
+ landlock_get_current_domain();
+
+ /* quick return if there is no domain or .scoped is not set */
+ if (!dom || !get_scoped_accesses(dom))
+ return true;
+
+ /* the credentials will not change */
+ lockdep_assert_held(&unix_sk(other)->lock);
+ if (other->sk_type != SOCK_DGRAM) {
+ dom_other = landlock_cred(other->sk_peer_cred)->domain;
+ } else {
+ dom_other =
+ landlock_cred(other->sk_socket->file->f_cred)->domain;
+ }
+
+ if (!dom_other || !get_scoped_accesses(dom_other))
+ return false;
+
+ /* other is scoped, they connect if they are in the same domain */
+ return domain_scope_le(dom, dom_other);
+}
+
+static int hook_unix_stream_connect(struct sock *const sock,
+ struct sock *const other,
+ struct sock *const newsk)
+{
+ if (sock_is_scoped(other))
+ return 0;
+
+ return -EPERM;
+}
+
+static int hook_unix_may_send(struct socket *const sock,
+ struct socket *const other)
+{
+ pr_warn("XXX %s:%d sock->file:%p other->file:%p\n", __func__, __LINE__,
+ sock->file, other->file);
+ if (sock_is_scoped(other->sk))
+ return 0;
+
+ return -EPERM;
+}
+
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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