mirror_ubuntu-kernels/security/apparmor/task.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * AppArmor security module
 *
 * This file contains AppArmor task related definitions and mediation
 *
 * Copyright 2017 Canonical Ltd.
 *
 * TODO
 * If a task uses change_hat it currently does not return to the old
 * cred or task context but instead creates a new one.  Ideally the task
 * should return to the previous cred if it has not been modified.
 */

#include <linux/gfp.h>
#include <linux/ptrace.h>

#include "include/audit.h"
#include "include/cred.h"
#include "include/policy.h"
#include "include/task.h"

/**
 * aa_get_task_label - Get another task's label
 * @task: task to query  (NOT NULL)
 *
 * Returns: counted reference to @task's label
 */
struct aa_label *aa_get_task_label(struct task_struct *task)
{
	struct aa_label *p;

	rcu_read_lock();
	p = aa_get_newest_cred_label(__task_cred(task));
	rcu_read_unlock();

	return p;
}

/**
 * aa_replace_current_label - replace the current tasks label
 * @label: new label  (NOT NULL)
 *
 * Returns: 0 or error on failure
 */
int aa_replace_current_label(struct aa_label *label)
{
	struct aa_label *old = aa_current_raw_label();
	struct aa_task_ctx *ctx = task_ctx(current);
	struct cred *new;

	AA_BUG(!label);

	if (old == label)
		return 0;

	if (current_cred() != current_real_cred())
		return -EBUSY;

	new  = prepare_creds();
	if (!new)
		return -ENOMEM;

	if (ctx->nnp && label_is_stale(ctx->nnp)) {
		struct aa_label *tmp = ctx->nnp;

		ctx->nnp = aa_get_newest_label(tmp);
		aa_put_label(tmp);
	}
	if (unconfined(label) || (labels_ns(old) != labels_ns(label)))
		/*
		 * if switching to unconfined or a different label namespace
		 * clear out context state
		 */
		aa_clear_task_ctx_trans(task_ctx(current));

	/*
	 * be careful switching cred label, when racing replacement it
	 * is possible that the cred labels's->proxy->label is the reference
	 * keeping @label valid, so make sure to get its reference before
	 * dropping the reference on the cred's label
	 */
	aa_get_label(label);
	aa_put_label(cred_label(new));
	set_cred_label(new, label);

	commit_creds(new);
	return 0;
}


/**
 * aa_set_current_onexec - set the tasks change_profile to happen onexec
 * @label: system label to set at exec  (MAYBE NULL to clear value)
 * @stack: whether stacking should be done
 */
void aa_set_current_onexec(struct aa_label *label, bool stack)
{
	struct aa_task_ctx *ctx = task_ctx(current);

	aa_get_label(label);
	aa_put_label(ctx->onexec);
	ctx->onexec = label;
	ctx->token = stack;
}

/**
 * aa_set_current_hat - set the current tasks hat
 * @label: label to set as the current hat  (NOT NULL)
 * @token: token value that must be specified to change from the hat
 *
 * Do switch of tasks hat.  If the task is currently in a hat
 * validate the token to match.
 *
 * Returns: 0 or error on failure
 */
int aa_set_current_hat(struct aa_label *label, u64 token)
{
	struct aa_task_ctx *ctx = task_ctx(current);
	struct cred *new;

	new = prepare_creds();
	if (!new)
		return -ENOMEM;
	AA_BUG(!label);

	if (!ctx->previous) {
		/* transfer refcount */
		ctx->previous = cred_label(new);
		ctx->token = token;
	} else if (ctx->token == token) {
		aa_put_label(cred_label(new));
	} else {
		/* previous_profile && ctx->token != token */
		abort_creds(new);
		return -EACCES;
	}

	set_cred_label(new, aa_get_newest_label(label));
	/* clear exec on switching context */
	aa_put_label(ctx->onexec);
	ctx->onexec = NULL;

	commit_creds(new);
	return 0;
}

/**
 * aa_restore_previous_label - exit from hat context restoring previous label
 * @token: the token that must be matched to exit hat context
 *
 * Attempt to return out of a hat to the previous label.  The token
 * must match the stored token value.
 *
 * Returns: 0 or error of failure
 */
int aa_restore_previous_label(u64 token)
{
	struct aa_task_ctx *ctx = task_ctx(current);
	struct cred *new;

	if (ctx->token != token)
		return -EACCES;
	/* ignore restores when there is no saved label */
	if (!ctx->previous)
		return 0;

	new = prepare_creds();
	if (!new)
		return -ENOMEM;

	aa_put_label(cred_label(new));
	set_cred_label(new, aa_get_newest_label(ctx->previous));
	AA_BUG(!cred_label(new));
	/* clear exec && prev information when restoring to previous context */
	aa_clear_task_ctx_trans(ctx);

	commit_creds(new);

	return 0;
}

/**
 * audit_ptrace_mask - convert mask to permission string
 * @mask: permission mask to convert
 *
 * Returns: pointer to static string
 */
static const char *audit_ptrace_mask(u32 mask)
{
	switch (mask) {
	case MAY_READ:
		return "read";
	case MAY_WRITE:
		return "trace";
	case AA_MAY_BE_READ:
		return "readby";
	case AA_MAY_BE_TRACED:
		return "tracedby";
	}
	return "";
}

/* call back to audit ptrace fields */
static void audit_ptrace_cb(struct audit_buffer *ab, void *va)
{
	struct common_audit_data *sa = va;
	struct apparmor_audit_data *ad = aad(sa);

	if (ad->request & AA_PTRACE_PERM_MASK) {
		audit_log_format(ab, " requested_mask=\"%s\"",
				 audit_ptrace_mask(ad->request));

		if (ad->denied & AA_PTRACE_PERM_MASK) {
			audit_log_format(ab, " denied_mask=\"%s\"",
					 audit_ptrace_mask(ad->denied));
		}
	}
	audit_log_format(ab, " peer=");
	aa_label_xaudit(ab, labels_ns(ad->subj_label), ad->peer,
			FLAGS_NONE, GFP_ATOMIC);
}

/* assumes check for RULE_MEDIATES is already done */
/* TODO: conditionals */
static int profile_ptrace_perm(const struct cred *cred,
			       struct aa_profile *profile,
			       struct aa_label *peer, u32 request,
			       struct apparmor_audit_data *ad)
{
	struct aa_ruleset *rules = list_first_entry(&profile->rules,
						    typeof(*rules), list);
	struct aa_perms perms = { };

	ad->subj_cred = cred;
	ad->peer = peer;
	aa_profile_match_label(profile, rules, peer, AA_CLASS_PTRACE, request,
			       &perms);
	aa_apply_modes_to_perms(profile, &perms);
	return aa_check_perms(profile, &perms, request, ad, audit_ptrace_cb);
}

static int profile_tracee_perm(const struct cred *cred,
			       struct aa_profile *tracee,
			       struct aa_label *tracer, u32 request,
			       struct apparmor_audit_data *ad)
{
	if (!profile_mediates(tracee, AA_CLASS_PTRACE) ||
	    !label_mediates(tracer, AA_CLASS_PTRACE))
		return 0;

	return profile_ptrace_perm(cred, tracee, tracer, request, ad);
}

static int profile_tracer_perm(const struct cred *cred,
			       struct aa_profile *tracer,
			       struct aa_label *tracee, u32 request,
			       struct apparmor_audit_data *ad)
{
	if (profile_mediates(tracer, AA_CLASS_PTRACE))
		return profile_ptrace_perm(cred, tracer, tracee, request, ad);

	/* profile uses the old style capability check for ptrace */
	if (&tracer->label == tracee || !profile_mediates(tracer, AA_CLASS_CAP))
		return 0;

	ad->subj_label = &tracer->label;
	ad->peer = tracee;
	ad->request = 0;
	ad->error = aa_capable(cred, &tracer->label, CAP_SYS_PTRACE,
			       CAP_OPT_NONE);

	return aa_audit(AUDIT_APPARMOR_AUTO, tracer, ad, audit_ptrace_cb);
}

/**
 * aa_may_ptrace - test if tracer task can trace the tracee
 * @tracer_cred: cred of task doing the tracing  (NOT NULL)
 * @tracer: label of the task doing the tracing  (NOT NULL)
 * @tracee_cred: cred of task to be traced
 * @tracee: task label to be traced
 * @request: permission request
 *
 * Returns: %0 else error code if permission denied or error
 */
int aa_may_ptrace(const struct cred *tracer_cred, struct aa_label *tracer,
		  const struct cred *tracee_cred, struct aa_label *tracee,
		  u32 request)
{
	struct aa_profile *profile;
	u32 xrequest = request << PTRACE_PERM_SHIFT;
	DEFINE_AUDIT_DATA(sa, LSM_AUDIT_DATA_NONE, AA_CLASS_PTRACE, OP_PTRACE);

	return xcheck_labels(tracer, tracee, profile,
			profile_tracer_perm(tracer_cred, profile, tracee,
					    request, &sa),
			profile_tracee_perm(tracee_cred, profile, tracer,
					    xrequest, &sa));
}

/* call back to audit ptrace fields */
static void audit_ns_cb(struct audit_buffer *ab, void *va)
{
	struct apparmor_audit_data *ad = aad_of_va(va);

	if (ad->request & AA_USERNS_CREATE)
		audit_log_format(ab, " requested=\"userns_create\"");

	if (ad->denied & AA_USERNS_CREATE)
		audit_log_format(ab, " denied=\"userns_create\"");

	if (ad->peer) {
		audit_log_format(ab, " target=");
		aa_label_xaudit(ab, labels_ns(ad->subj_label), ad->peer,
				FLAG_VIEW_SUBNS, GFP_KERNEL);
	} else if (ad->ns.target) {
		audit_log_format(ab, " target=");
		audit_log_untrustedstring(ab, ad->ns.target);
	}

}

/*
 * Returns: refcounted label to change to, even if no change
 *          PTR_ERR on failure
 */
static struct aa_label *ns_x_to_label(struct aa_profile *profile,
				      u32 xindex, const char **lookupname,
				      const char **info)
{
	struct aa_ruleset *rules = list_first_entry(&profile->rules,
						    typeof(*rules), list);
	struct aa_label *new = NULL;
	u32 xtype = xindex & AA_X_TYPE_MASK;
	struct aa_label *stack = NULL;

	/* must be none or table */
	switch (xtype) {
	case AA_X_NONE:
		/* default not failure */
		*lookupname = NULL;
		return NULL;
		break;
	case AA_X_TABLE:
		/* TODO: fix when perm mapping done at unload */
		/* released by caller
		 * if null for both stack and direct want to try fallback
		 */
		new = x_table_lookup(profile, xindex, lookupname);
		if (!new) {
			*info = "failed to find transition profile";
			return ERR_PTR(-ENOMEM);
		}
		if (**lookupname == '&') {
			stack = new;
			new = NULL;
		}
		break;
	default:
		*info = "invalid profile transition type";
		return ERR_PTR(-EINVAL);
		break;
	}

	/* stack is true if !new */
	if (!new) {
		if (xindex & AA_X_UNCONFINED) {
			new = aa_get_newest_label(ns_unconfined(profile->ns));
			*info = "ux fallback";
		} else {
			if (xindex & AA_X_INHERIT) {
				/* (p|c|n)ix - don't change profile but do
				 * use the newest version
				 */
				*info = "ix fallback";
				/* no profile && no error */
			} /* else, stack is implicitly against current */
			new = aa_get_newest_label(&profile->label);
		}
	}

	if (stack) {
		/* base the stack on post domain transition */
		struct aa_label *base = new;

		new = aa_label_merge(base, stack, GFP_KERNEL);
		/* null on error */
		aa_put_label(base);
		aa_put_label(stack);
		if (!new)
			return ERR_PTR(-ENOMEM);
	}

	/* released by caller */
	return new;
}

struct aa_label *aa_profile_ns_perm(struct aa_profile *profile,
				    struct apparmor_audit_data *ad,
				    u32 request)
{
	struct aa_ruleset *rules = list_first_entry(&profile->rules,
						    typeof(*rules), list);
	struct aa_label *new;
	struct aa_perms perms = { };
	aa_state_t state;

	ad->subj_label = &profile->label;
	ad->request = request;
	int error;

	/* TODO: rework unconfined profile/dfa to mediate user ns, then
	 * we can drop the unconfined test
	 */
	state = RULE_MEDIATES(rules, ad->class);
	if (!state) {
		/* TODO: this gets replaced when the default unconfined
		 * profile dfa gets updated to handle this
		 */
		if (profile_unconfined(profile) &&
		    profile == profiles_ns(profile)->unconfined) {
			if (!aa_unprivileged_userns_restricted ||
			    ns_capable_noaudit(current_user_ns(),
					       CAP_SYS_ADMIN))
				return aa_get_newest_label(&profile->label);
			ad->info = "User namespace creation restricted";
			/* unconfined unprivileged user */
			/* don't just return: allow complain mode to override */
// hardcode unconfined transition for now
			new = aa_label_parse(&profile->label,
					     "unprivileged_userns", GFP_KERNEL,
					     true, false);
			if (IS_ERR(new)) {
				ad->info = "Userns create restricted - failed to find unprivileged_userns profile";
				ad->error = PTR_ERR(new);
				ad->ns.target = "unprivileged_userns";
				new = NULL;
				perms.deny |= request;
				goto hard_coded;
			}
			ad->info = "Userns create - transitioning profile";
			perms.audit = request;
			perms.allow = request;
			goto hard_coded;
// once we have special unconfined profile, jump to ns_x_to_label()
// end hardcode
		} else if (!aa_unprivileged_userns_restricted_force) {
			return aa_get_newest_label(&profile->label);
		}
		/* continue to mediation */
	}

	perms = *aa_lookup_perms(rules->policy, state);
	new = ns_x_to_label(profile, perms.xindex, &ad->ns.target, &ad->info);
	if (IS_ERR(new)) {
		ad->error = PTR_ERR(new);
		new = NULL;
		perms.deny |= request;
	} else if (!new) {
		/* no transition - not done in x_to_label so we can track */
		new = aa_get_label(&profile->label);
	} else {
hard_coded:
		ad->peer = new;
	}
	if (aa_unprivileged_userns_restricted_complain)
		perms.complain = ALL_PERMS_MASK;
	// TODO: nnp
	// TODO: complain mode support for transitions

	aa_apply_modes_to_perms(profile, &perms);
	error = aa_check_perms(profile, &perms, request, ad, audit_ns_cb);
	if (error) {
		aa_put_label(new);
		return ERR_PTR(error);
	}
	return new;
}