>From 2901842a561ee3d205f93f9ba543741f82edf65d Mon Sep 17 00:00:00 2001 Message-Id: <2901842a561ee3d205f93f9ba543741f82edf65d.1720203255.git.fahimitahera@gmail.com> In-Reply-To: References: From: Tahera Fahimi Date: Fri, 21 Jun 2024 15:23:17 -0600 Subject: [PATCH 1/2] Landlock: Add abstract unix socket connect restriction 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) Signed-off-by: Tahera Fahimi ------- 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 --- 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 #include #include +#include +#include #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