apparmor: add fine grained af_unix mediation

Extend af_unix mediation to support fine grained controls based on
the type (abstract, anonymous, fs), the address, and the labeling
on the socket.

This allows for using socket addresses to label and the socket and
control which subjects can communicate.

The unix rule format follows standard apparmor rules except that fs
based unix sockets can be mediated by existing file rules. None fs
unix sockets can be mediated by a unix socket rule. Where The address
of an abstract unix domain socket begins with the @ character, similar
to how they are reported (as paths) by netstat -x.  The address then
follows and may contain pattern matching and any characters including
the null character. In apparmor null characters must be specified by
using an escape sequence \000 or \x00. The pattern matching is the
same as is used by file path matching so * will not match / even
though it has no special meaning with in an abstract socket name. Eg.

     allow unix addr=@*,

Autobound unix domain sockets have a unix sun_path assigned to them by
the kernel, as such specifying a policy based address is not possible.
The autobinding of sockets can be controlled by specifying the special
auto keyword. Eg.

     allow unix addr=auto,

To indicate that the rule only applies to auto binding of unix domain
sockets.  It is important to note this only applies to the bind
permission as once the socket is bound to an address it is
indistinguishable from a socket that have an addr bound with a
specified name. When the auto keyword is used with other permissions
or as part of a peer addr it will be replaced with a pattern that can
match an autobound socket. Eg. For some kernels

    allow unix rw addr=auto,

It is important to note, this pattern may match abstract sockets that
were not autobound but have an addr that fits what is generated by the
kernel when autobinding a socket.

Anonymous unix domain sockets have no sun_path associated with the
socket address, however it can be specified with the special none
keyword to indicate the rule only applies to anonymous unix domain
sockets. Eg.

    allow unix addr=none,

If the address component of a rule is not specified then the rule
applies to autobind, abstract and anonymous sockets.

The label on the socket can be compared using the standard label=
rule conditional. Eg.

    allow unix addr=@foo peer=(label=bar),

see man apparmor.d for full syntax description.

Signed-off-by: John Johansen <john.johansen@canonical.com>

1 files changed, 702 insertions, 0 deletions

diff --git a/security/apparmor/af_unix.c b/security/apparmor/af_unix.c
new file mode 100644
index 000000000000..ce7dc9d98fb1
--- /dev/null
+++ b/security/apparmor/af_unix.c
@@ -0,0 +1,702 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * AppArmor security module
+ *
+ * This file contains AppArmor af_unix fine grained mediation
+ *
+ * Copyright 2023 Canonical Ltd.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation, version 2 of the
+ * License.
+ */
+
+#include <net/tcp_states.h>
+
+#include "include/audit.h"
+#include "include/af_unix.h"
+#include "include/apparmor.h"
+#include "include/file.h"
+#include "include/label.h"
+#include "include/path.h"
+#include "include/policy.h"
+#include "include/cred.h"
+
+
+static inline struct sock *aa_unix_sk(struct unix_sock *u)
+{
+	return &u->sk;
+}
+
+static int unix_fs_perm(const char *op, u32 mask, const struct cred *subj_cred,
+			struct aa_label *label, struct unix_sock *u)
+{
+	AA_BUG(!label);
+	AA_BUG(!u);
+	AA_BUG(!is_unix_fs(aa_unix_sk(u)));
+
+	if (unconfined(label) || !label_mediates(label, AA_CLASS_FILE))
+		return 0;
+
+	mask &= NET_FS_PERMS;
+	/* if !u->path.dentry socket is being shutdown - implicit delegation
+	 * until obj delegation is supported
+	 */
+	if (u->path.dentry) {
+		/* the sunpath may not be valid for this ns so use the path */
+		struct path_cond cond = { u->path.dentry->d_inode->i_uid,
+					  u->path.dentry->d_inode->i_mode
+		};
+
+		return aa_path_perm(op, subj_cred, label, &u->path,
+				    PATH_SOCK_COND, mask, &cond);
+	} /* else implicitly delegated */
+
+	return 0;
+}
+
+/* match_addr special constants */
+#define ABSTRACT_ADDR "\x00"		/* abstract socket addr */
+#define ANONYMOUS_ADDR "\x01"		/* anonymous endpoint, no addr */
+#define DISCONNECTED_ADDR "\x02"	/* addr is another namespace */
+#define SHUTDOWN_ADDR "\x03"		/* path addr is shutdown and cleared */
+#define FS_ADDR "/"			/* path addr in fs */
+
+static aa_state_t match_addr(struct aa_dfa *dfa, aa_state_t state,
+			     struct sockaddr_un *addr, int addrlen)
+{
+	if (addr)
+		/* include leading \0 */
+		state = aa_dfa_match_len(dfa, state, addr->sun_path,
+					 unix_addr_len(addrlen));
+	else
+		state = aa_dfa_match_len(dfa, state, ANONYMOUS_ADDR, 1);
+	/* todo: could change to out of band for cleaner separation */
+	state = aa_dfa_null_transition(dfa, state);
+
+	return state;
+}
+
+static aa_state_t match_to_local(struct aa_policydb *policy,
+				 aa_state_t state, u32 request,
+				 int type, int protocol,
+				 struct sockaddr_un *addr, int addrlen,
+				 struct aa_perms **p,
+				 const char **info)
+{
+	state = aa_match_to_prot(policy, state, request, PF_UNIX, type,
+				 protocol, NULL, info);
+	if (state) {
+		state = match_addr(policy->dfa, state, addr, addrlen);
+		if (state) {
+			/* todo: local label matching */
+			state = aa_dfa_null_transition(policy->dfa, state);
+			if (!state)
+				*info = "failed local label match";
+		} else {
+			*info = "failed local address match";
+		}
+	}
+
+	return state;
+}
+
+static aa_state_t match_to_sk(struct aa_policydb *policy,
+			      aa_state_t state, u32 request,
+			      struct unix_sock *u, struct aa_perms **p,
+			      const char **info)
+{
+	struct sockaddr_un *addr = NULL;
+	int addrlen = 0;
+
+	if (u->addr) {
+		addr = u->addr->name;
+		addrlen = u->addr->len;
+	}
+
+	return match_to_local(policy, state, request, u->sk.sk_type,
+			      u->sk.sk_protocol, addr, addrlen, p, info);
+}
+
+#define CMD_ADDR	1
+#define CMD_LISTEN	2
+#define CMD_OPT		4
+
+static aa_state_t match_to_cmd(struct aa_policydb *policy, aa_state_t state,
+			       u32 request, struct unix_sock *u,
+			       char cmd, struct aa_perms **p,
+			       const char **info)
+{
+	AA_BUG(!p);
+
+	state = match_to_sk(policy, state, request, u, p, info);
+	if (state && !*p) {
+		state = aa_dfa_match_len(policy->dfa, state, &cmd, 1);
+		if (!state)
+			*info = "failed cmd selection match";
+	}
+
+	return state;
+}
+
+static aa_state_t match_to_peer(struct aa_policydb *policy, aa_state_t state,
+				u32 request, struct unix_sock *u,
+				struct sockaddr_un *peer_addr, int peer_addrlen,
+				struct aa_perms **p, const char **info)
+{
+	AA_BUG(!p);
+
+	state = match_to_cmd(policy, state, request, u, CMD_ADDR, p, info);
+	if (state && !*p) {
+		state = match_addr(policy->dfa, state, peer_addr, peer_addrlen);
+		if (!state)
+			*info = "failed peer address match";
+	}
+
+	return state;
+}
+
+static aa_state_t match_label(struct aa_profile *profile,
+			      struct aa_ruleset *rule, aa_state_t state,
+			      u32 request, struct aa_profile *peer,
+			      struct aa_perms *p,
+			      struct apparmor_audit_data *ad)
+{
+	AA_BUG(!profile);
+	AA_BUG(!peer);
+
+	ad->peer = &peer->label;
+
+	if (state && !p) {
+		state = aa_dfa_match(rule->policy->dfa, state,
+				     peer->base.hname);
+		if (!state)
+			ad->info = "failed peer label match";
+
+	}
+
+	return aa_do_perms(profile, rule->policy, state, request, p, ad);
+}
+
+
+/* unix sock creation comes before we know if the socket will be an fs
+ * socket
+ * v6 - semantics are handled by mapping in profile load
+ * v7 - semantics require sock create for tasks creating an fs socket.
+ * v8 - same as v7
+ */
+static int profile_create_perm(struct aa_profile *profile, int family,
+			       int type, int protocol,
+			       struct apparmor_audit_data *ad)
+{
+	struct aa_ruleset *rules = list_first_entry(&profile->rules,
+						    typeof(*rules), list);
+	aa_state_t state;
+
+	AA_BUG(!profile);
+	AA_BUG(profile_unconfined(profile));
+
+	state = RULE_MEDIATES_NET(rules);
+	if (state) {
+		state = aa_match_to_prot(rules->policy, state, AA_MAY_CREATE,
+					 PF_UNIX, type, protocol, NULL,
+					 &ad->info);
+
+		return aa_do_perms(profile, rules->policy, state, AA_MAY_CREATE,
+				   NULL, ad);
+	}
+
+	return aa_profile_af_perm(profile, ad, AA_MAY_CREATE, family, type,
+				  protocol);
+}
+
+static int profile_sk_perm(struct aa_profile *profile,
+			   struct apparmor_audit_data *ad,
+			   u32 request, struct sock *sk)
+{
+	struct aa_ruleset *rules = list_first_entry(&profile->rules,
+						    typeof(*rules),
+						    list);
+	struct aa_perms *p = NULL;
+	aa_state_t state;
+
+	AA_BUG(!profile);
+	AA_BUG(!sk);
+	AA_BUG(is_unix_fs(sk));
+	AA_BUG(profile_unconfined(profile));
+
+	state = RULE_MEDIATES_NET(rules);
+	if (state) {
+		state = match_to_sk(rules->policy, state, request, unix_sk(sk),
+				    &p, &ad->info);
+
+		return aa_do_perms(profile, rules->policy, state, request, p,
+				   ad);
+	}
+
+	return aa_profile_af_sk_perm(profile, ad, request, sk);
+}
+
+static int profile_bind_perm(struct aa_profile *profile, struct sock *sk,
+			     struct apparmor_audit_data *ad)
+{
+	struct aa_ruleset *rules = list_first_entry(&profile->rules,
+						    typeof(*rules), list);
+	struct aa_perms *p = NULL;
+	aa_state_t state;
+
+	AA_BUG(!profile);
+	AA_BUG(!sk);
+	AA_BUG(!ad);
+	AA_BUG(profile_unconfined(profile));
+
+	state = RULE_MEDIATES_NET(rules);
+	if (state) {
+		/* bind for abstract socket */
+		state = match_to_local(rules->policy, state, AA_MAY_BIND,
+				       sk->sk_type, sk->sk_protocol,
+				       unix_addr(ad->net.addr),
+				       ad->net.addrlen,
+				       &p, &ad->info);
+
+		return aa_do_perms(profile, rules->policy, state, AA_MAY_BIND,
+				   p, ad);
+	}
+
+	return aa_profile_af_sk_perm(profile, ad, AA_MAY_BIND, sk);
+}
+
+static int profile_listen_perm(struct aa_profile *profile, struct sock *sk,
+			       int backlog, struct apparmor_audit_data *ad)
+{
+	struct aa_ruleset *rules = list_first_entry(&profile->rules,
+						    typeof(*rules), list);
+	struct aa_perms *p = NULL;
+	aa_state_t state;
+
+	AA_BUG(!profile);
+	AA_BUG(!sk);
+	AA_BUG(is_unix_fs(sk));
+	AA_BUG(!ad);
+	AA_BUG(profile_unconfined(profile));
+
+	state = RULE_MEDIATES_NET(rules);
+	if (state) {
+		__be16 b = cpu_to_be16(backlog);
+
+		state = match_to_cmd(rules->policy, state, AA_MAY_LISTEN,
+				     unix_sk(sk), CMD_LISTEN, &p, &ad->info);
+		if (state && !p) {
+			state = aa_dfa_match_len(rules->policy->dfa, state,
+						 (char *) &b, 2);
+			if (!state)
+				ad->info = "failed listen backlog match";
+		}
+		return aa_do_perms(profile, rules->policy, state, AA_MAY_LISTEN,
+				   p, ad);
+	}
+
+	return aa_profile_af_sk_perm(profile, ad, AA_MAY_LISTEN, sk);
+}
+
+static int profile_accept_perm(struct aa_profile *profile,
+			       struct sock *sk,
+			       struct apparmor_audit_data *ad)
+{
+	struct aa_ruleset *rules = list_first_entry(&profile->rules,
+						    typeof(*rules), list);
+	struct aa_perms *p = NULL;
+	aa_state_t state;
+
+	AA_BUG(!profile);
+	AA_BUG(!sk);
+	AA_BUG(is_unix_fs(sk));
+	AA_BUG(!ad);
+	AA_BUG(profile_unconfined(profile));
+
+	state = RULE_MEDIATES_NET(rules);
+	if (state) {
+		state = match_to_sk(rules->policy, state, AA_MAY_ACCEPT,
+				    unix_sk(sk), &p, &ad->info);
+
+		return aa_do_perms(profile, rules->policy, state, AA_MAY_ACCEPT,
+				   p, ad);
+	}
+
+	return aa_profile_af_sk_perm(profile, ad, AA_MAY_ACCEPT, sk);
+}
+
+static int profile_opt_perm(struct aa_profile *profile, u32 request,
+			    struct sock *sk, int optname,
+			    struct apparmor_audit_data *ad)
+{
+	struct aa_ruleset *rules = list_first_entry(&profile->rules,
+						    typeof(*rules), list);
+	struct aa_perms *p = NULL;
+	aa_state_t state;
+
+	AA_BUG(!profile);
+	AA_BUG(!sk);
+	AA_BUG(is_unix_fs(sk));
+	AA_BUG(!ad);
+	AA_BUG(profile_unconfined(profile));
+
+	state = RULE_MEDIATES_NET(rules);
+	if (state) {
+		__be16 b = cpu_to_be16(optname);
+
+		state = match_to_cmd(rules->policy, state, request, unix_sk(sk),
+				     CMD_OPT, &p, &ad->info);
+		if (state && !p) {
+			state = aa_dfa_match_len(rules->policy->dfa, state,
+						 (char *) &b, 2);
+			if (!state)
+				ad->info = "failed sockopt match";
+		}
+		return aa_do_perms(profile, rules->policy, state, request, p,
+				   ad);
+	}
+
+	return aa_profile_af_sk_perm(profile, ad, request, sk);
+}
+
+/* null peer_label is allowed, in which case the peer_sk label is used */
+static int profile_peer_perm(struct aa_profile *profile, u32 request,
+			     struct sock *sk, struct sock *peer_sk,
+			     struct aa_label *peer_label,
+			     struct apparmor_audit_data *ad)
+{
+	struct aa_ruleset *rules = list_first_entry(&profile->rules,
+						    typeof(*rules), list);
+	struct aa_perms *p = NULL;
+	aa_state_t state;
+
+	AA_BUG(!profile);
+	AA_BUG(profile_unconfined(profile));
+	AA_BUG(!sk);
+	AA_BUG(!peer_sk);
+	AA_BUG(!ad);
+	AA_BUG(is_unix_fs(peer_sk)); /* currently always calls unix_fs_perm */
+
+	state = RULE_MEDIATES_NET(rules);
+	if (state) {
+		struct aa_sk_ctx *peer_ctx = aa_sock(peer_sk);
+		struct aa_profile *peerp;
+		struct sockaddr_un *addr = NULL;
+		int len = 0;
+
+		if (unix_sk(peer_sk)->addr) {
+			addr = unix_sk(peer_sk)->addr->name;
+			len = unix_sk(peer_sk)->addr->len;
+		}
+		state = match_to_peer(rules->policy, state, request,
+				      unix_sk(sk),
+				      addr, len, &p, &ad->info);
+		if (!peer_label)
+			peer_label = peer_ctx->label;
+
+		return fn_for_each_in_ns(peer_label, peerp,
+				match_label(profile, rules, state, request,
+					    peerp, p, ad));
+	}
+
+	return aa_profile_af_sk_perm(profile, ad, request, sk);
+}
+
+/* -------------------------------- */
+
+int aa_unix_create_perm(struct aa_label *label, int family, int type,
+			int protocol)
+{
+	if (!unconfined(label)) {
+		struct aa_profile *profile;
+		DEFINE_AUDIT_NET(ad, OP_CREATE, current_cred(), NULL, family,
+				 type, protocol);
+
+		return fn_for_each_confined(label, profile,
+				profile_create_perm(profile, family, type,
+						    protocol, &ad));
+	}
+
+	return 0;
+}
+
+int aa_unix_label_sk_perm(const struct cred *subj_cred,
+			  struct aa_label *label, const char *op, u32 request,
+			  struct sock *sk)
+{
+	if (!unconfined(label)) {
+		struct aa_profile *profile;
+		DEFINE_AUDIT_SK(ad, op, subj_cred, sk);
+
+		return fn_for_each_confined(label, profile,
+				profile_sk_perm(profile, &ad, request, sk));
+	}
+	return 0;
+}
+
+static int unix_label_sock_perm(const struct cred *subj_cred,
+				struct aa_label *label, const char *op,
+				u32 request, struct socket *sock)
+{
+	if (unconfined(label))
+		return 0;
+	if (is_unix_fs(sock->sk))
+		return unix_fs_perm(op, request, subj_cred, label,
+				    unix_sk(sock->sk));
+
+	return aa_unix_label_sk_perm(subj_cred, label, op, request, sock->sk);
+}
+
+/* revalidation, get/set attr, shutdown */
+int aa_unix_sock_perm(const char *op, u32 request, struct socket *sock)
+{
+	struct aa_label *label;
+	int error;
+
+	label = begin_current_label_crit_section();
+	error = unix_label_sock_perm(current_cred(), label, op, request, sock);
+	end_current_label_crit_section(label);
+
+	return error;
+}
+
+static int valid_addr(struct sockaddr *addr, int addr_len)
+{
+	struct sockaddr_un *sunaddr = (struct sockaddr_un *)addr;
+
+	/* addr_len == offsetof(struct sockaddr_un, sun_path) is autobind */
+	if (addr_len < offsetof(struct sockaddr_un, sun_path) ||
+	    addr_len > sizeof(*sunaddr))
+		return -EINVAL;
+	return 0;
+}
+
+int aa_unix_bind_perm(struct socket *sock, struct sockaddr *addr,
+		      int addrlen)
+{
+	struct aa_profile *profile;
+	struct aa_label *label;
+	int error = 0;
+
+	error = valid_addr(addr, addrlen);
+	if (error)
+		return error;
+
+	label = begin_current_label_crit_section();
+	/* fs bind is handled by mknod */
+	if (!(unconfined(label) || is_unix_addr_fs(addr, addrlen))) {
+		DEFINE_AUDIT_SK(ad, OP_BIND, current_cred(), sock->sk);
+
+		ad.net.addr = unix_addr(addr);
+		ad.net.addrlen = addrlen;
+
+		error = fn_for_each_confined(label, profile,
+				profile_bind_perm(profile, sock->sk, &ad));
+	}
+	end_current_label_crit_section(label);
+
+	return error;
+}
+
+/*
+ * unix connections are covered by the
+ * - unix_stream_connect (stream) and unix_may_send hooks (dgram)
+ * - fs connect is handled by open
+ * This is just here to document this is not needed for af_unix
+ *
+int aa_unix_connect_perm(struct socket *sock, struct sockaddr *address,
+			 int addrlen)
+{
+	return 0;
+}
+*/
+
+int aa_unix_listen_perm(struct socket *sock, int backlog)
+{
+	struct aa_profile *profile;
+	struct aa_label *label;
+	int error = 0;
+
+	label = begin_current_label_crit_section();
+	if (!(unconfined(label) || is_unix_fs(sock->sk))) {
+		DEFINE_AUDIT_SK(ad, OP_LISTEN, current_cred(), sock->sk);
+
+		error = fn_for_each_confined(label, profile,
+				profile_listen_perm(profile, sock->sk,
+						    backlog, &ad));
+	}
+	end_current_label_crit_section(label);
+
+	return error;
+}
+
+
+/* ability of sock to connect, not peer address binding */
+int aa_unix_accept_perm(struct socket *sock, struct socket *newsock)
+{
+	struct aa_profile *profile;
+	struct aa_label *label;
+	int error = 0;
+
+	label = begin_current_label_crit_section();
+	if (!(unconfined(label) || is_unix_fs(sock->sk))) {
+		DEFINE_AUDIT_SK(ad, OP_ACCEPT, current_cred(), sock->sk);
+
+		error = fn_for_each_confined(label, profile,
+				profile_accept_perm(profile, sock->sk, &ad));
+	}
+	end_current_label_crit_section(label);
+
+	return error;
+}
+
+
+/*
+ * dgram handled by unix_may_sendmsg, right to send on stream done at connect
+ * could do per msg unix_stream here, but connect + socket transfer is
+ * sufficient. This is just here to document this is not needed for af_unix
+ *
+ * sendmsg, recvmsg
+int aa_unix_msg_perm(const char *op, u32 request, struct socket *sock,
+		     struct msghdr *msg, int size)
+{
+	return 0;
+}
+*/
+
+int aa_unix_opt_perm(const char *op, u32 request, struct socket *sock,
+		     int level, int optname)
+{
+	struct aa_profile *profile;
+	struct aa_label *label;
+	int error = 0;
+
+	label = begin_current_label_crit_section();
+	if (!(unconfined(label) || is_unix_fs(sock->sk))) {
+		DEFINE_AUDIT_SK(ad, op, current_cred(), sock->sk);
+
+		error = fn_for_each_confined(label, profile,
+					     profile_opt_perm(profile, request,
+						 sock->sk, optname, &ad));
+	}
+	end_current_label_crit_section(label);
+
+	return error;
+}
+
+/**
+ *
+ * Requires: lock held on both @sk and @peer_sk
+ *           called by unix_stream_connect, unix_may_send
+ */
+int aa_unix_peer_perm(const struct cred *subj_cred,
+		      struct aa_label *label, const char *op, u32 request,
+		      struct sock *sk, struct sock *peer_sk,
+		      struct aa_label *peer_label)
+{
+	struct unix_sock *peeru = unix_sk(peer_sk);
+	struct unix_sock *u = unix_sk(sk);
+
+	AA_BUG(!label);
+	AA_BUG(!sk);
+	AA_BUG(!peer_sk);
+
+	if (is_unix_fs(aa_unix_sk(peeru))) {
+		return unix_fs_perm(op, request, subj_cred, label, peeru);
+	} else if (is_unix_fs(aa_unix_sk(u))) {
+		return unix_fs_perm(op, request, subj_cred, label, u);
+	} else if (!unconfined(label)) {
+		struct aa_profile *profile;
+		DEFINE_AUDIT_SK(ad, op, subj_cred, sk);
+
+		ad.net.peer_sk = peer_sk;
+
+		return fn_for_each_confined(label, profile,
+				profile_peer_perm(profile, request, sk,
+						  peer_sk, peer_label, &ad));
+	}
+
+	return 0;
+}
+
+static void unix_state_double_lock(struct sock *sk1, struct sock *sk2)
+{
+	if (unlikely(sk1 == sk2) || !sk2) {
+		unix_state_lock(sk1);
+		return;
+	}
+	if (sk1 < sk2) {
+		unix_state_lock(sk1);
+		unix_state_lock(sk2);
+	} else {
+		unix_state_lock(sk2);
+		unix_state_lock(sk1);
+	}
+}
+
+static void unix_state_double_unlock(struct sock *sk1, struct sock *sk2)
+{
+	if (unlikely(sk1 == sk2) || !sk2) {
+		unix_state_unlock(sk1);
+		return;
+	}
+	unix_state_unlock(sk1);
+	unix_state_unlock(sk2);
+}
+
+/* TODO: examine replacing double lock with cached addr */
+
+int aa_unix_file_perm(const struct cred *subj_cred, struct aa_label *label,
+		      const char *op, u32 request, struct file *file)
+{
+	struct socket *sock = (struct socket *) file->private_data;
+	struct sock *peer_sk = NULL;
+	u32 sk_req = request & ~NET_PEER_MASK;
+	bool is_sk_fs;
+	int error = 0;
+
+	AA_BUG(!label);
+	AA_BUG(!sock);
+	AA_BUG(!sock->sk);
+	AA_BUG(sock->sk->sk_family != PF_UNIX);
+
+	/* TODO: update sock label with new task label */
+	unix_state_lock(sock->sk);
+	peer_sk = unix_peer(sock->sk);
+	if (peer_sk)
+		sock_hold(peer_sk);
+
+	is_sk_fs = is_unix_fs(sock->sk);
+	if (is_sk_fs && peer_sk)
+		sk_req = request;
+	if (sk_req)
+		error = unix_label_sock_perm(subj_cred, label, op, sk_req,
+					     sock);
+	unix_state_unlock(sock->sk);
+	if (!peer_sk)
+		return error;
+
+	unix_state_double_lock(sock->sk, peer_sk);
+	if (!is_sk_fs && is_unix_fs(peer_sk)) {
+		last_error(error,
+			   unix_fs_perm(op, request, subj_cred, label,
+					unix_sk(peer_sk)));
+	} else if (!is_sk_fs) {
+		struct aa_sk_ctx *pctx = aa_sock(peer_sk);
+
+		last_error(error,
+			xcheck(aa_unix_peer_perm(subj_cred, label, op,
+						 MAY_READ | MAY_WRITE,
+						 sock->sk, peer_sk, NULL),
+			       aa_unix_peer_perm(file->f_cred, pctx->label, op,
+						 MAY_READ | MAY_WRITE,
+						 peer_sk, sock->sk, label)));
+	}
+	unix_state_double_unlock(sock->sk, peer_sk);
+
+	sock_put(peer_sk);
+
+	return error;
+}