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AJvYcCXYRKK+I4RH+FgWkCRyn0FhF8wrh9ZK43axtqoc9iAZkVH0+qXpbC8yCeaE034PXgYW8RSBvPEd6VoIRPy55T4P+GLvU1DDx2iXiS5K7l323KjelP4dZcW5g/6WS18w7pF3t/WHLrn37uejnzbNXxNXiafU1jGX0NhpN/xRNxuLvsLa4n/01QSC1TAH X-Gm-Message-State: AOJu0YzdHQHtyP/Gwy8JWXMkNhdOA2c9WUoSJmwCeVukRLtb8ilxAWWr 2F7Medv2AgvXkuuEvsOPZ1KbHxS4z78rWh+EJp/66YuXziptr831 X-Google-Smtp-Source: AGHT+IFVoZPochyOfuDQ+SlstEbMIoO1KxFIxh7A1gCZ0HELnXmlpRbHjIqEFQp2l1KO0DZPRNgxTQ== X-Received: by 2002:a05:6871:23c1:b0:268:9d6b:672 with SMTP id 586e51a60fabf-2689d6b4e84mr556145fac.42.1722571388699; Thu, 01 Aug 2024 21:03:08 -0700 (PDT) Received: from tahera-OptiPlex-5000.tail3bf47f.ts.net ([136.159.49.123]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7106ec41465sm542099b3a.60.2024.08.01.21.03.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Aug 2024 21:03:07 -0700 (PDT) From: Tahera Fahimi To: outreachy@lists.linux.dev Cc: mic@digikod.net, gnoack@google.com, paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, bjorn3_gh@protonmail.com, jannh@google.com, netdev@vger.kernel.org, Tahera Fahimi Subject: [PATCH v8 1/4] Landlock: Add abstract unix socket connect restriction Date: Thu, 1 Aug 2024 22:02:33 -0600 Message-Id: X-Mailer: git-send-email 2.34.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 This patch introduces a new "scoped" attribute to the landlock_ruleset_attr that can specify "LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET" to scope abstract Unix sockets from connecting to a process outside of the same landlock domain. It implements two hooks, unix_stream_connect and unix_may_send to enforce this restriction. Closes: https://github.com/landlock-lsm/linux/issues/7 Signed-off-by: Tahera Fahimi --- v8: - Code refactoring (improve code readability, renaming variable, etc.) based on reviews by Mickaël Salaün on version 7. - Adding warn_on_once to check (impossible) inconsistencies. - Adding inline comments. - Adding check_unix_address_format to check if the scoping socket is an abstract unix sockets. v7: - Using socket's file credentials for both connected(STREAM) and non-connected(DGRAM) sockets. - Adding "domain_sock_scope" instead of the domain scoping mechanism used in ptrace ensures that if a server's domain is accessible from the client's domain (where the client is more privileged than the server), the client can connect to the server in all edge cases. - Removing debug codes. v6: - Removing curr_ruleset from landlock_hierarchy, and switching back to use the same domain scoping as ptrace. - code clean up. v5: - Renaming "LANDLOCK_*_ACCESS_SCOPE" to "LANDLOCK_*_SCOPE" - Adding curr_ruleset to hierarachy_ruleset structure to have access from landlock_hierarchy to its respective landlock_ruleset. - Using curr_ruleset to check if a domain is scoped while walking in the hierarchy of domains. - Modifying inline comments. V4: - Rebased on Günther's Patch: https://lore.kernel.org/all/20240610082115.1693267-1-gnoack@google.com/ so there is no need for "LANDLOCK_SHIFT_ACCESS_SCOPE", then it is removed. - Adding get_scope_accesses function to check all scoped access masks in a ruleset. - Using socket's file credentials instead of credentials stored in peer_cred for datagram sockets. (see discussion in [1]) - Modifying inline comments. V3: - Improving commit description. - Introducing "scoped" attribute to landlock_ruleset_attr for IPC scoping purpose, and adding related functions. - Changing structure of ruleset based on "scoped". - Removing rcu lock and using unix_sk lock instead. - Introducing scoping for datagram sockets in unix_may_send. V2: - Removing wrapper functions [1]https://lore.kernel.org/all/20240610.Aifee5ingugh@digikod.net/ ---- --- include/uapi/linux/landlock.h | 30 +++++++ security/landlock/limits.h | 3 + security/landlock/ruleset.c | 7 +- security/landlock/ruleset.h | 23 ++++- security/landlock/syscalls.c | 14 ++- security/landlock/task.c | 155 ++++++++++++++++++++++++++++++++++ 6 files changed, 225 insertions(+), 7 deletions(-) diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h index 68625e728f43..ab31e9f53e55 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 +272,28 @@ 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 + * non-sandboxed process). + */ +/* 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..f51b29521d6b 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 @@ -170,7 +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 unknown 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..7e8579ebae83 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 +110,162 @@ static int hook_ptrace_traceme(struct task_struct *const parent) return task_ptrace(parent, current); } +static bool walk_and_check(const struct landlock_ruleset *const child, + struct landlock_hierarchy **walker, + size_t base_layer, size_t deep_layer, + access_mask_t check_scoping) +{ + if (!child || base_layer < 0 || !(*walker)) + return false; + + for (deep_layer; base_layer < deep_layer; deep_layer--) { + if (check_scoping & landlock_get_scope_mask(child, deep_layer)) + return false; + *walker = (*walker)->parent; + if (WARN_ON_ONCE(!*walker)) + /* there is an inconsistency between num_layers + * and landlock_hierarchy in the ruleset + */ + return false; + } + return true; +} + +/** + * domain_IPC_scope - Checks if the client domain is scoped in the same + * domain as the server. + * + * @client: IPC sender domain. + * @server: IPC receiver domain. + * + * Check if the @client domain is scoped to access the @server; the @server + * must be scoped in the same domain. + */ +static bool domain_IPC_scope(const struct landlock_ruleset *const client, + const struct landlock_ruleset *const server, + access_mask_t ipc_type) +{ + size_t client_layer, server_layer = 0; + int base_layer; + struct landlock_hierarchy *client_walker, *server_walker; + bool is_scoped; + + /* Quick return if client has no domain */ + if (!client) + return true; + + client_layer = client->num_layers - 1; + client_walker = client->hierarchy; + if (server) { + server_layer = server->num_layers - 1; + server_walker = server->hierarchy; + } + base_layer = (client_layer > server_layer) ? server_layer : + client_layer; + + /* For client domain, walk_and_check ensures the client domain is + * not scoped until gets to base_layer. + * For server_domain, it only ensures that the server domain exist. + */ + if (client_layer != server_layer) { + if (client_layer > server_layer) + is_scoped = walk_and_check(client, &client_walker, + server_layer, client_layer, + ipc_type); + else + is_scoped = walk_and_check(server, &server_walker, + client_layer, server_layer, + ipc_type & 0); + if (!is_scoped) + return false; + } + /* client and server are at the same level in hierarchy. If client is + * scoped, the server must be scoped in the same domain + */ + for (base_layer; base_layer >= 0; base_layer--) { + if (landlock_get_scope_mask(client, base_layer) & ipc_type) { + /* This check must be here since access would be denied only if + * the client is scoped and the server has no domain, so + * if the client has a domain but is not scoped and the server + * has no domain, access is guaranteed. + */ + if (!server) + return false; + + if (server_walker == client_walker) + return true; + + return false; + } + client_walker = client_walker->parent; + server_walker = server_walker->parent; + /* Warn if there is an incosistenncy between num_layers and + * landlock_hierarchy in each of rulesets + */ + if (WARN_ON_ONCE(base_layer > 0 && + (!server_walker || !client_walker))) + return false; + } + return true; +} + +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(); + + /* 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_IPC_scope(dom, dom_other, + LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET); +} + +static bool check_unix_address_format(struct sock *const sock) +{ + struct unix_address *addr = unix_sk(sock)->addr; + + if (!addr) + return true; + + if (addr->len > sizeof(AF_UNIX)) { + /* handling unspec sockets */ + if (!addr->name[0].sun_path) + return true; + + if (addr->name[0].sun_path[0] == '\0') + if (!sock_is_scoped(sock)) + return false; + } + + return true; +} + +static int hook_unix_stream_connect(struct sock *const sock, + struct sock *const other, + struct sock *const newsk) +{ + if (check_unix_address_format(other)) + return 0; + + return -EPERM; +} + +static int hook_unix_may_send(struct socket *const sock, + struct socket *const other) +{ + if (check_unix_address_format(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)