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Hallyn" , outreachy@lists.linux.dev, Jann Horn , netdev@vger.kernel.org, =?iso-8859-1?q?Bj=F6r?= =?iso-8859-1?q?n?= Roy Baron Subject: [PATCH v3] landlock: Add abstract unix socket connect restriction Message-ID: Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline Abstract unix sockets are used for local inter-process communications without on a filesystem. Currently a sandboxed process can connect to a socket outside of the sandboxed environment, since landlock has no restriction for connecting to a unix socket in the abstract namespace. 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. 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) Closes: https://github.com/landlock-lsm/linux/issues/7 Signed-off-by: Tahera Fahimi ------- V3: Added "scoped" field to landlock_ruleset_attr V2: Remove wrapper functions ------- --- include/uapi/linux/landlock.h | 28 +++++++++++++++++++++++ security/landlock/limits.h | 5 ++++ security/landlock/ruleset.c | 15 ++++++++---- security/landlock/ruleset.h | 28 +++++++++++++++++++++-- security/landlock/syscalls.c | 12 +++++++--- security/landlock/task.c | 43 +++++++++++++++++++++++++++++++++++ 6 files changed, 121 insertions(+), 10 deletions(-) diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h index 68625e728f43..d887e67dc0ed 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 actions (cf. `Scope access flags`_) + * that is handled by this ruleset and should be permitted + * by default if no rule explicitly deny them. + */ + __u64 scoped; }; /* @@ -266,4 +272,26 @@ 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: scoped + * + * Scoped handles a set of restrictions on kernel IPCs. + * + * Scope access flags + * ~~~~~~~~~~~~~~~~~~~~ + * + * These flags enable to restrict a sandboxed process from a set of + * inter-process communications actions. Setting a flag in a landlock + * domain will isolate the Landlock domain to forbid connections + * to resources outside the domain. + * + * IPCs with scoped actions: + * - %LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET: Restrict a sandbox process to + * connect to a process outside of the sandbox domain through abstract + * unix sockets. + */ +/* 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 20fdb5ff3514..7b794b81ef05 100644 --- a/security/landlock/limits.h +++ b/security/landlock/limits.h @@ -28,6 +28,11 @@ #define LANDLOCK_NUM_ACCESS_NET __const_hweight64(LANDLOCK_MASK_ACCESS_NET) #define LANDLOCK_SHIFT_ACCESS_NET LANDLOCK_NUM_ACCESS_FS +#define LANDLOCK_LAST_ACCESS_SCOPE LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET +#define LANDLOCK_MASK_ACCESS_SCOPE ((LANDLOCK_LAST_ACCESS_SCOPE << 1) - 1) +#define LANDLOCK_NUM_ACCESS_SCOPE __const_hweight64(LANDLOCK_MASK_ACCESS_SCOPE) +#define LANDLOCK_SHIFT_ACCESS_SCOPE LANDLOCK_SHIFT_ACCESS_NET + /* clang-format on */ #endif /* _SECURITY_LANDLOCK_LIMITS_H */ diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c index e0a5fbf9201a..635d0854be09 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; } @@ -173,9 +176,11 @@ static void build_check_ruleset(void) BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES); BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS); - BUILD_BUG_ON(access_masks < - ((LANDLOCK_MASK_ACCESS_FS << LANDLOCK_SHIFT_ACCESS_FS) | - (LANDLOCK_MASK_ACCESS_NET << LANDLOCK_SHIFT_ACCESS_NET))); + BUILD_BUG_ON( + access_masks < + ((LANDLOCK_MASK_ACCESS_FS << LANDLOCK_SHIFT_ACCESS_FS) | + (LANDLOCK_MASK_ACCESS_NET << LANDLOCK_SHIFT_ACCESS_NET) | + (LANDLOCK_MASK_ACCESS_SCOPE << LANDLOCK_SHIFT_ACCESS_SCOPE))); } /** diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h index c7f1526784fd..b633d1b66452 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_ACCESS_SCOPE); /* Makes sure for_each_set_bit() and for_each_clear_bit() calls are OK. */ static_assert(sizeof(unsigned long) >= sizeof(access_mask_t)); @@ -42,7 +44,8 @@ static_assert(sizeof(unsigned long) >= sizeof(access_mask_t)); typedef u32 access_masks_t; /* Makes sure all ruleset access rights can be stored. */ static_assert(BITS_PER_TYPE(access_masks_t) >= - LANDLOCK_NUM_ACCESS_FS + LANDLOCK_NUM_ACCESS_NET); + LANDLOCK_NUM_ACCESS_FS + LANDLOCK_NUM_ACCESS_NET + + LANDLOCK_NUM_ACCESS_SCOPE); typedef u16 layer_mask_t; /* Makes sure all layers can be checked. */ @@ -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); @@ -282,6 +286,17 @@ landlock_add_net_access_mask(struct landlock_ruleset *const ruleset, (net_mask << LANDLOCK_SHIFT_ACCESS_NET); } +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_ACCESS_SCOPE; + + WARN_ON_ONCE(scope_mask != scoped_mask); + ruleset->access_masks[layer_level] |= + (scoped_mask << LANDLOCK_SHIFT_ACCESS_SCOPE); +} + static inline access_mask_t landlock_get_raw_fs_access_mask(const struct landlock_ruleset *const ruleset, const u16 layer_level) @@ -309,6 +324,15 @@ landlock_get_net_access_mask(const struct landlock_ruleset *const ruleset, LANDLOCK_MASK_ACCESS_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] >> + LANDLOCK_SHIFT_ACCESS_SCOPE) & + LANDLOCK_MASK_ACCESS_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 03b470f5a85a..e95e79752be0 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. */ @@ -212,10 +213,15 @@ SYSCALL_DEFINE3(landlock_create_ruleset, if ((ruleset_attr.handled_access_net | LANDLOCK_MASK_ACCESS_NET) != LANDLOCK_MASK_ACCESS_NET) return -EINVAL; + /* Checks IPC scoping content (and 32-bits cast). */ + if ((ruleset_attr.scoped | LANDLOCK_MASK_ACCESS_SCOPE) != + LANDLOCK_MASK_ACCESS_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..147c6545ef24 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 +110,50 @@ static int hook_ptrace_traceme(struct task_struct *const parent) return task_ptrace(parent, current); } +static bool sock_is_scoped(struct sock *const other) +{ + bool is_scoped = true; + const struct landlock_ruleset *dom_other; + const struct cred *cred_other; + + const struct landlock_ruleset *const dom = + landlock_get_current_domain(); + if (!dom) + return true; + + lockdep_assert_held(&unix_sk(other)->lock); + /* the credentials will not change */ + cred_other = get_cred(other->sk_peer_cred); + dom_other = landlock_cred(cred_other)->domain; + is_scoped = domain_scope_le(dom, dom_other); + put_cred(cred_other); + return is_scoped; +} + +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) +{ + 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)