From 54a6e6bbf3bef25c8eb65619edde70af49bd3db0 Mon Sep 17 00:00:00 2001 From: Tahera Fahimi Date: Fri, 6 Sep 2024 15:30:03 -0600 Subject: [PATCH] landlock: Add signal scoping MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 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 Signed-off-by: Mickaël Salaün --- 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) {