From 21d52e295ad2afc76bbd105da82a003b96f6ac77 Mon Sep 17 00:00:00 2001 From: Tahera Fahimi Date: Wed, 4 Sep 2024 18:13:55 -0600 Subject: landlock: Add abstract UNIX socket scoping MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Introduce a new "scoped" member to landlock_ruleset_attr that can specify LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET to restrict connection to abstract UNIX sockets from a process outside of the socket's domain. Two hooks are implemented to enforce these restrictions: unix_stream_connect and unix_may_send. Closes: https://github.com/landlock-lsm/linux/issues/7 Signed-off-by: Tahera Fahimi Link: https://lore.kernel.org/r/5f7ad85243b78427242275b93481cfc7c127764b.1725494372.git.fahimitahera@gmail.com [mic: Fix commit message formatting, improve documentation, simplify hook_unix_may_send(), and cosmetic fixes including rename of LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET] Co-developed-by: Mickaël Salaün Signed-off-by: Mickaël Salaün --- security/landlock/limits.h | 3 + security/landlock/ruleset.c | 7 ++- security/landlock/ruleset.h | 24 +++++++- security/landlock/syscalls.c | 17 ++++-- security/landlock/task.c | 137 +++++++++++++++++++++++++++++++++++++++++++ 5 files changed, 180 insertions(+), 8 deletions(-) (limited to 'security') diff --git a/security/landlock/limits.h b/security/landlock/limits.h index 4eb643077a2a..d74818003ed4 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_SCOPE_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..61bdbc550172 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 scope : 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 +284,17 @@ 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 mask = scope_mask & LANDLOCK_MASK_SCOPE; + + /* Should already be checked in sys_landlock_create_ruleset(). */ + WARN_ON_ONCE(scope_mask != mask); + ruleset->access_masks[layer_level].scope |= mask; +} + static inline access_mask_t landlock_get_raw_fs_access_mask(const struct landlock_ruleset *const ruleset, const u16 layer_level) @@ -303,6 +318,13 @@ 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].scope; +} + 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 ccc8bc6c1584..c67836841e46 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); @@ -149,7 +150,7 @@ static const struct file_operations ruleset_fops = { .write = fop_dummy_write, }; -#define LANDLOCK_ABI_VERSION 5 +#define LANDLOCK_ABI_VERSION 6 /** * sys_landlock_create_ruleset - Create a new ruleset @@ -170,8 +171,9 @@ 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; - * - %E2BIG or %EFAULT: @attr or @size inconsistencies; + * - %EINVAL: unknown @flags, or unknown access, or unknown scope, or too small @size; + * - %E2BIG: @attr or @size inconsistencies; + * - %EFAULT: @attr or @size inconsistencies; * - %ENOMSG: empty &landlock_ruleset_attr.handled_access_fs. */ SYSCALL_DEFINE3(landlock_create_ruleset, @@ -213,9 +215,14 @@ 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..4f8013ca412e 100644 --- a/security/landlock/task.c +++ b/security/landlock/task.c @@ -13,6 +13,8 @@ #include #include #include +#include +#include #include "common.h" #include "cred.h" @@ -108,9 +110,144 @@ static int hook_ptrace_traceme(struct task_struct *const parent) return task_ptrace(parent, current); } +/** + * domain_is_scoped - Checks if the client domain is scoped in the same + * domain as the server. + * + * @client: IPC sender domain. + * @server: IPC receiver domain. + * @scope: The scope restriction criteria. + * + * Returns: True if the @client domain is scoped to access the @server, + * unless the @server is also scoped in the same domain as @client. + */ +static bool domain_is_scoped(const struct landlock_ruleset *const client, + const struct landlock_ruleset *const server, + access_mask_t scope) +{ + int client_layer, server_layer; + struct landlock_hierarchy *client_walker, *server_walker; + + /* Quick return if client has no domain */ + if (WARN_ON_ONCE(!client)) + return false; + + client_layer = client->num_layers - 1; + client_walker = client->hierarchy; + /* + * client_layer must be a signed integer with greater capacity + * than client->num_layers to ensure the following loop stops. + */ + BUILD_BUG_ON(sizeof(client_layer) > sizeof(client->num_layers)); + + server_layer = server ? (server->num_layers - 1) : -1; + server_walker = server ? server->hierarchy : NULL; + + /* + * Walks client's parent domains down to the same hierarchy level + * as the server's domain, and checks that none of these client's + * parent domains are scoped. + */ + for (; client_layer > server_layer; client_layer--) { + if (landlock_get_scope_mask(client, client_layer) & scope) + return true; + + client_walker = client_walker->parent; + } + /* + * Walks server's parent domains down to the same hierarchy level as + * the client's domain. + */ + for (; server_layer > client_layer; server_layer--) + server_walker = server_walker->parent; + + for (; client_layer >= 0; client_layer--) { + if (landlock_get_scope_mask(client, client_layer) & scope) { + /* + * Client and server are at the same level in the + * hierarchy. If the client is scoped, the request is + * only allowed if this domain is also a server's + * ancestor. + */ + return server_walker != client_walker; + } + client_walker = client_walker->parent; + server_walker = server_walker->parent; + } + return false; +} + +static bool sock_is_scoped(struct sock *const other, + const struct landlock_ruleset *const domain) +{ + const struct landlock_ruleset *dom_other; + + /* The credentials will not change. */ + lockdep_assert_held(&unix_sk(other)->lock); + dom_other = landlock_cred(other->sk_socket->file->f_cred)->domain; + return domain_is_scoped(domain, dom_other, + LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET); +} + +static bool is_abstract_socket(struct sock *const sock) +{ + struct unix_address *addr = unix_sk(sock)->addr; + + if (!addr) + return false; + + if (addr->len >= offsetof(struct sockaddr_un, sun_path) + 1 && + addr->name->sun_path[0] == '\0') + return true; + + return false; +} + +static int hook_unix_stream_connect(struct sock *const sock, + struct sock *const other, + struct sock *const newsk) +{ + const struct landlock_ruleset *const dom = + landlock_get_current_domain(); + + /* Quick return for non-landlocked tasks. */ + if (!dom) + return 0; + + if (is_abstract_socket(other) && sock_is_scoped(other, dom)) + return -EPERM; + + return 0; +} + +static int hook_unix_may_send(struct socket *const sock, + struct socket *const other) +{ + const struct landlock_ruleset *const dom = + landlock_get_current_domain(); + + if (!dom) + return 0; + + /* + * Checks if this datagram socket was already allowed to be connected + * to other. + */ + if (unix_peer(sock->sk) == other->sk) + return 0; + + if (is_abstract_socket(other->sk) && sock_is_scoped(other->sk, dom)) + 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), }; __init void landlock_add_task_hooks(void) -- cgit v1.2.3-70-g09d2 From 54a6e6bbf3bef25c8eb65619edde70af49bd3db0 Mon Sep 17 00:00:00 2001 From: Tahera Fahimi Date: Fri, 6 Sep 2024 15:30:03 -0600 Subject: 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 ++++++++++++++++++++++++++ tools/testing/selftests/landlock/scoped_test.c | 2 +- 7 files changed, 94 insertions(+), 3 deletions(-) (limited to 'security') 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) { -- cgit v1.2.3-70-g09d2