From 54a6e6bbf3bef25c8eb65619edde70af49bd3db0 Mon Sep 17 00:00:00 2001
From: Tahera Fahimi <fahimitahera@gmail.com>
Date: Fri, 6 Sep 2024 15:30:03 -0600
Subject: [PATCH] landlock: Add signal scoping
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Currently, a sandbox process is not restricted to sending a signal (e.g.
SIGKILL) to a process outside the sandbox environment. The ability to
send a signal for a sandboxed process should be scoped the same way
abstract UNIX sockets are scoped. Therefore, we extend the "scoped"
field in a ruleset with LANDLOCK_SCOPE_SIGNAL to specify that a ruleset
will deny sending any signal from within a sandbox process to its parent
(i.e. any parent sandbox or non-sandboxed processes).
This patch adds file_set_fowner and file_free_security hooks to set and
release a pointer to the file owner's domain. This pointer, fown_domain
in landlock_file_security will be used in file_send_sigiotask to check
if the process can send a signal.
The ruleset_with_unknown_scope test is updated to support
LANDLOCK_SCOPE_SIGNAL.
This depends on two new changes:
- commit 1934b212615d ("file: reclaim 24 bytes from f_owner"): replace
container_of(fown, struct file, f_owner) with fown->file .
- commit 26f204380a3c ("fs: Fix file_set_fowner LSM hook
inconsistencies"): lock before calling the hook.
Signed-off-by: Tahera Fahimi <fahimitahera@gmail.com>
Closes: https://github.com/landlock-lsm/linux/issues/8
Link: https://lore.kernel.org/r/df2b4f880a2ed3042992689a793ea0951f6798a5.1725657727.git.fahimitahera@gmail.com
[mic: Update landlock_get_current_domain()'s return type, improve and
fix locking in hook_file_set_fowner(), simplify and fix sleepable call
and locking issue in hook_file_send_sigiotask() and rebase on the latest
VFS tree, simplify hook_task_kill() and quickly return when not
sandboxed, improve comments, rename LANDLOCK_SCOPED_SIGNAL]
Co-developed-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
---
include/uapi/linux/landlock.h | 3 +
security/landlock/cred.h | 2 +-
security/landlock/fs.c | 25 +++++++++
security/landlock/fs.h | 7 +++
security/landlock/limits.h | 2 +-
security/landlock/task.c | 56 +++++++++++++++++++
.../testing/selftests/landlock/scoped_test.c | 2 +-
7 files changed, 94 insertions(+), 3 deletions(-)
diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
index 70edd17bafdc..33745642f787 100644
--- a/include/uapi/linux/landlock.h
+++ b/include/uapi/linux/landlock.h
@@ -296,9 +296,12 @@ struct landlock_net_port_attr {
* - %LANDLOCK_SCOPE_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 non-sandboxed process).
+ * - %LANDLOCK_SCOPE_SIGNAL: Restrict a sandboxed process from sending a signal
+ * to another process outside the domain.
*/
/* clang-format off */
#define LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET (1ULL << 0)
+#define LANDLOCK_SCOPE_SIGNAL (1ULL << 1)
/* clang-format on*/
#endif /* _UAPI_LINUX_LANDLOCK_H */
diff --git a/security/landlock/cred.h b/security/landlock/cred.h
index af89ab00e6d1..bf755459838a 100644
--- a/security/landlock/cred.h
+++ b/security/landlock/cred.h
@@ -26,7 +26,7 @@ landlock_cred(const struct cred *cred)
return cred->security + landlock_blob_sizes.lbs_cred;
}
-static inline const struct landlock_ruleset *landlock_get_current_domain(void)
+static inline struct landlock_ruleset *landlock_get_current_domain(void)
{
return landlock_cred(current_cred())->domain;
}
diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 0804f76a67be..7d79fc8abe21 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -1639,6 +1639,29 @@ static int hook_file_ioctl_compat(struct file *file, unsigned int cmd,
return -EACCES;
}
+static void hook_file_set_fowner(struct file *file)
+{
+ struct landlock_ruleset *new_dom, *prev_dom;
+
+ /*
+ * Lock already held by __f_setown(), see commit 26f204380a3c ("fs: Fix
+ * file_set_fowner LSM hook inconsistencies").
+ */
+ lockdep_assert_held(&file_f_owner(file)->lock);
+ new_dom = landlock_get_current_domain();
+ landlock_get_ruleset(new_dom);
+ prev_dom = landlock_file(file)->fown_domain;
+ landlock_file(file)->fown_domain = new_dom;
+
+ /* Called in an RCU read-side critical section. */
+ landlock_put_ruleset_deferred(prev_dom);
+}
+
+static void hook_file_free_security(struct file *file)
+{
+ landlock_put_ruleset_deferred(landlock_file(file)->fown_domain);
+}
+
static struct security_hook_list landlock_hooks[] __ro_after_init = {
LSM_HOOK_INIT(inode_free_security_rcu, hook_inode_free_security_rcu),
@@ -1663,6 +1686,8 @@ static struct security_hook_list landlock_hooks[] __ro_after_init = {
LSM_HOOK_INIT(file_truncate, hook_file_truncate),
LSM_HOOK_INIT(file_ioctl, hook_file_ioctl),
LSM_HOOK_INIT(file_ioctl_compat, hook_file_ioctl_compat),
+ LSM_HOOK_INIT(file_set_fowner, hook_file_set_fowner),
+ LSM_HOOK_INIT(file_free_security, hook_file_free_security),
};
__init void landlock_add_fs_hooks(void)
diff --git a/security/landlock/fs.h b/security/landlock/fs.h
index 488e4813680a..1487e1f023a1 100644
--- a/security/landlock/fs.h
+++ b/security/landlock/fs.h
@@ -52,6 +52,13 @@ struct landlock_file_security {
* needed to authorize later operations on the open file.
*/
access_mask_t allowed_access;
+ /**
+ * @fown_domain: Domain of the task that set the PID that may receive a
+ * signal e.g., SIGURG when writing MSG_OOB to the related socket.
+ * This pointer is protected by the related file->f_owner->lock, as for
+ * fown_struct's members: pid, uid, and euid.
+ */
+ struct landlock_ruleset *fown_domain;
};
/**
diff --git a/security/landlock/limits.h b/security/landlock/limits.h
index d74818003ed4..15f7606066c8 100644
--- a/security/landlock/limits.h
+++ b/security/landlock/limits.h
@@ -26,7 +26,7 @@
#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_SCOPE_ABSTRACT_UNIX_SOCKET
+#define LANDLOCK_LAST_SCOPE LANDLOCK_SCOPE_SIGNAL
#define LANDLOCK_MASK_SCOPE ((LANDLOCK_LAST_SCOPE << 1) - 1)
#define LANDLOCK_NUM_SCOPE __const_hweight64(LANDLOCK_MASK_SCOPE)
/* clang-format on */
diff --git a/security/landlock/task.c b/security/landlock/task.c
index 4f8013ca412e..4acbd7c40eee 100644
--- a/security/landlock/task.c
+++ b/security/landlock/task.c
@@ -18,6 +18,7 @@
#include "common.h"
#include "cred.h"
+#include "fs.h"
#include "ruleset.h"
#include "setup.h"
#include "task.h"
@@ -242,12 +243,67 @@ static int hook_unix_may_send(struct socket *const sock,
return 0;
}
+static int hook_task_kill(struct task_struct *const p,
+ struct kernel_siginfo *const info, const int sig,
+ const struct cred *const cred)
+{
+ bool is_scoped;
+ const struct landlock_ruleset *dom;
+
+ if (cred) {
+ /* Dealing with USB IO. */
+ dom = landlock_cred(cred)->domain;
+ } else {
+ dom = landlock_get_current_domain();
+ }
+
+ /* Quick return for non-landlocked tasks. */
+ if (!dom)
+ return 0;
+
+ rcu_read_lock();
+ is_scoped = domain_is_scoped(dom, landlock_get_task_domain(p),
+ LANDLOCK_SCOPE_SIGNAL);
+ rcu_read_unlock();
+ if (is_scoped)
+ return -EPERM;
+
+ return 0;
+}
+
+static int hook_file_send_sigiotask(struct task_struct *tsk,
+ struct fown_struct *fown, int signum)
+{
+ const struct landlock_ruleset *dom;
+ bool is_scoped = false;
+
+ /* Lock already held by send_sigio() and send_sigurg(). */
+ lockdep_assert_held(&fown->lock);
+ dom = landlock_file(fown->file)->fown_domain;
+
+ /* Quick return for unowned socket. */
+ if (!dom)
+ return 0;
+
+ rcu_read_lock();
+ is_scoped = domain_is_scoped(dom, landlock_get_task_domain(tsk),
+ LANDLOCK_SCOPE_SIGNAL);
+ rcu_read_unlock();
+ if (is_scoped)
+ return -EPERM;
+
+ return 0;
+}
+
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),
+
+ LSM_HOOK_INIT(task_kill, hook_task_kill),
+ LSM_HOOK_INIT(file_send_sigiotask, hook_file_send_sigiotask),
};
__init void landlock_add_task_hooks(void)
diff --git a/tools/testing/selftests/landlock/scoped_test.c b/tools/testing/selftests/landlock/scoped_test.c
index 2d15f09d63e2..b90f76ed0d9c 100644
--- a/tools/testing/selftests/landlock/scoped_test.c
+++ b/tools/testing/selftests/landlock/scoped_test.c
@@ -12,7 +12,7 @@
#include "common.h"
-#define ACCESS_LAST LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET
+#define ACCESS_LAST LANDLOCK_SCOPE_SIGNAL
TEST(ruleset_with_unknown_scope)
{
--
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