selinux: revert SECINITSID_INIT support

This commit reverts 5b0eea8 ("selinux: introduce an initial SID
for early boot processes") as it was found to cause problems on
distros with old SELinux userspace tools/libraries, specifically
Ubuntu 16.04.

Hopefully we will be able to re-add this functionality at a later
date, but let's revert this for now to help ensure a stable and
backwards compatible SELinux tree.

Link: https://lore.kernel.org/selinux/87edkseqf8.fsf@mail.lhotse
Acked-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

Author: pcmoore

security/selinux/hooks.c

@@ -2313,19 +2313,6 @@ static int selinux_bprm_creds_for_exec(struct linux_binprm *bprm)
 	new_tsec->keycreate_sid = 0;
 	new_tsec->sockcreate_sid = 0;
 
-	/*
-	 * Before policy is loaded, label any task outside kernel space
-	 * as SECINITSID_INIT, so that any userspace tasks surviving from
-	 * early boot end up with a label different from SECINITSID_KERNEL
-	 * (if the policy chooses to set SECINITSID_INIT != SECINITSID_KERNEL).
-	 */
-	if (!selinux_initialized()) {
-		new_tsec->sid = SECINITSID_INIT;
-		/* also clear the exec_sid just in case */
-		new_tsec->exec_sid = 0;
-		return 0;
-	}
-
 	if (old_tsec->exec_sid) {
 		new_tsec->sid = old_tsec->exec_sid;
 		/* Reset exec SID on execve. */
@@ -4542,21 +4529,6 @@ static int sock_has_perm(struct sock *sk, u32 perms)
 	if (sksec->sid == SECINITSID_KERNEL)
 		return 0;
 
-	/*
-	 * Before POLICYDB_CAP_USERSPACE_INITIAL_CONTEXT, sockets that
-	 * inherited the kernel context from early boot used to be skipped
-	 * here, so preserve that behavior unless the capability is set.
-	 *
-	 * By setting the capability the policy signals that it is ready
-	 * for this quirk to be fixed. Note that sockets created by a kernel
-	 * thread or a usermode helper executed without a transition will
-	 * still be skipped in this check regardless of the policycap
-	 * setting.
-	 */
-	if (!selinux_policycap_userspace_initial_context() &&
-	    sksec->sid == SECINITSID_INIT)
-		return 0;
-
 	ad_net_init_from_sk(&ad, &net, sk);
 
 	return avc_has_perm(current_sid(), sksec->sid, sksec->sclass, perms,

security/selinux/include/initial_sid_to_string.h

@@ -10,7 +10,7 @@ static const char *const initial_sid_to_string[] = {
 	NULL,
 	"file",
 	NULL,
-	"init",
+	NULL,
 	"any_socket",
 	"port",
 	"netif",

security/selinux/include/policycap.h

@@ -12,7 +12,6 @@ enum {
 	POLICYDB_CAP_NNP_NOSUID_TRANSITION,
 	POLICYDB_CAP_GENFS_SECLABEL_SYMLINKS,
 	POLICYDB_CAP_IOCTL_SKIP_CLOEXEC,
-	POLICYDB_CAP_USERSPACE_INITIAL_CONTEXT,
 	__POLICYDB_CAP_MAX
 };
 #define POLICYDB_CAP_MAX (__POLICYDB_CAP_MAX - 1)

security/selinux/include/policycap_names.h

@@ -14,7 +14,6 @@ const char *const selinux_policycap_names[__POLICYDB_CAP_MAX] = {
 	"nnp_nosuid_transition",
 	"genfs_seclabel_symlinks",
 	"ioctl_skip_cloexec",
-	"userspace_initial_context",
 };
 
 #endif /* _SELINUX_POLICYCAP_NAMES_H_ */

security/selinux/include/security.h

@@ -189,12 +189,6 @@ static inline bool selinux_policycap_ioctl_skip_cloexec(void)
 		selinux_state.policycap[POLICYDB_CAP_IOCTL_SKIP_CLOEXEC]);
 }
 
-static inline bool selinux_policycap_userspace_initial_context(void)
-{
-	return READ_ONCE(
-		selinux_state.policycap[POLICYDB_CAP_USERSPACE_INITIAL_CONTEXT]);
-}
-
 struct selinux_policy_convert_data;
 
 struct selinux_load_state {

security/selinux/ss/policydb.c

@@ -864,8 +864,6 @@ void policydb_destroy(struct policydb *p)
 int policydb_load_isids(struct policydb *p, struct sidtab *s)
 {
 	struct ocontext *head, *c;
-	bool isid_init_supported = ebitmap_get_bit(&p->policycaps,
-						   POLICYDB_CAP_USERSPACE_INITIAL_CONTEXT);
 	int rc;
 
 	rc = sidtab_init(s);
@@ -889,38 +887,13 @@ int policydb_load_isids(struct policydb *p, struct sidtab *s)
 		if (!name)
 			continue;
 
-		/*
-		 * Also ignore SECINITSID_INIT if the policy doesn't declare
-		 * support for it
-		 */
-		if (sid == SECINITSID_INIT && !isid_init_supported)
-			continue;
-
 		rc = sidtab_set_initial(s, sid, &c->context[0]);
 		if (rc) {
 			pr_err("SELinux:  unable to load initial SID %s.\n",
 			       name);
 			sidtab_destroy(s);
 			return rc;
 		}
-
-		/*
-		 * If the policy doesn't support the "userspace_initial_context"
-		 * capability, set SECINITSID_INIT to the same context as
-		 * SECINITSID_KERNEL. This ensures the same behavior as before
-		 * the reintroduction of SECINITSID_INIT, where all tasks
-		 * started before policy load would initially get the context
-		 * corresponding to SECINITSID_KERNEL.
-		 */
-		if (sid == SECINITSID_KERNEL && !isid_init_supported) {
-			rc = sidtab_set_initial(s, SECINITSID_INIT, &c->context[0]);
-			if (rc) {
-				pr_err("SELinux:  unable to load initial SID %s.\n",
-				       name);
-				sidtab_destroy(s);
-				return rc;
-			}
-		}
 	}
 	return 0;
 }