task.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * AppArmor security module
  4 *
  5 * This file contains AppArmor task related definitions and mediation
  6 *
  7 * Copyright 2017 Canonical Ltd.
  8 *
  9 * TODO
 10 * If a task uses change_hat it currently does not return to the old
 11 * cred or task context but instead creates a new one.  Ideally the task
 12 * should return to the previous cred if it has not been modified.
 13 */
 14
 15#include <linux/gfp.h>
 16#include <linux/ptrace.h>
 17
 18#include "include/audit.h"
 19#include "include/cred.h"
 20#include "include/policy.h"
 21#include "include/task.h"
 22
 23/**
 24 * aa_get_task_label - Get another task's label
 25 * @task: task to query  (NOT NULL)
 26 *
 27 * Returns: counted reference to @task's label
 28 */
 29struct aa_label *aa_get_task_label(struct task_struct *task)
 30{
 31	struct aa_label *p;
 32
 33	rcu_read_lock();
 34	p = aa_get_newest_cred_label(__task_cred(task));
 35	rcu_read_unlock();
 36
 37	return p;
 38}
 39
 40/**
 41 * aa_replace_current_label - replace the current tasks label
 42 * @label: new label  (NOT NULL)
 43 *
 44 * Returns: 0 or error on failure
 45 */
 46int aa_replace_current_label(struct aa_label *label)
 47{
 48	struct aa_label *old = aa_current_raw_label();
 49	struct aa_task_ctx *ctx = task_ctx(current);
 50	struct cred *new;
 51
 52	AA_BUG(!label);
 53
 54	if (old == label)
 55		return 0;
 56
 57	if (current_cred() != current_real_cred())
 58		return -EBUSY;
 59
 60	new  = prepare_creds();
 61	if (!new)
 62		return -ENOMEM;
 63
 64	if (ctx->nnp && label_is_stale(ctx->nnp)) {
 65		struct aa_label *tmp = ctx->nnp;
 66
 67		ctx->nnp = aa_get_newest_label(tmp);
 68		aa_put_label(tmp);
 69	}
 70	if (unconfined(label) || (labels_ns(old) != labels_ns(label)))
 71		/*
 72		 * if switching to unconfined or a different label namespace
 73		 * clear out context state
 74		 */
 75		aa_clear_task_ctx_trans(task_ctx(current));
 76
 77	/*
 78	 * be careful switching cred label, when racing replacement it
 79	 * is possible that the cred labels's->proxy->label is the reference
 80	 * keeping @label valid, so make sure to get its reference before
 81	 * dropping the reference on the cred's label
 82	 */
 83	aa_get_label(label);
 84	aa_put_label(cred_label(new));
 85	set_cred_label(new, label);
 86
 87	commit_creds(new);
 88	return 0;
 89}
 90
 91
 92/**
 93 * aa_set_current_onexec - set the tasks change_profile to happen onexec
 94 * @label: system label to set at exec  (MAYBE NULL to clear value)
 95 * @stack: whether stacking should be done
 96 */
 97void aa_set_current_onexec(struct aa_label *label, bool stack)
 98{
 99	struct aa_task_ctx *ctx = task_ctx(current);
100
101	aa_get_label(label);
102	aa_put_label(ctx->onexec);
103	ctx->onexec = label;
104	ctx->token = stack;
105}
106
107/**
108 * aa_set_current_hat - set the current tasks hat
109 * @label: label to set as the current hat  (NOT NULL)
110 * @token: token value that must be specified to change from the hat
111 *
112 * Do switch of tasks hat.  If the task is currently in a hat
113 * validate the token to match.
114 *
115 * Returns: 0 or error on failure
116 */
117int aa_set_current_hat(struct aa_label *label, u64 token)
118{
119	struct aa_task_ctx *ctx = task_ctx(current);
120	struct cred *new;
121
122	new = prepare_creds();
123	if (!new)
124		return -ENOMEM;
125	AA_BUG(!label);
126
127	if (!ctx->previous) {
128		/* transfer refcount */
129		ctx->previous = cred_label(new);
130		ctx->token = token;
131	} else if (ctx->token == token) {
132		aa_put_label(cred_label(new));
133	} else {
134		/* previous_profile && ctx->token != token */
135		abort_creds(new);
136		return -EACCES;
137	}
138
139	set_cred_label(new, aa_get_newest_label(label));
140	/* clear exec on switching context */
141	aa_put_label(ctx->onexec);
142	ctx->onexec = NULL;
143
144	commit_creds(new);
145	return 0;
146}
147
148/**
149 * aa_restore_previous_label - exit from hat context restoring previous label
150 * @token: the token that must be matched to exit hat context
151 *
152 * Attempt to return out of a hat to the previous label.  The token
153 * must match the stored token value.
154 *
155 * Returns: 0 or error of failure
156 */
157int aa_restore_previous_label(u64 token)
158{
159	struct aa_task_ctx *ctx = task_ctx(current);
160	struct cred *new;
161
162	if (ctx->token != token)
163		return -EACCES;
164	/* ignore restores when there is no saved label */
165	if (!ctx->previous)
166		return 0;
167
168	new = prepare_creds();
169	if (!new)
170		return -ENOMEM;
171
172	aa_put_label(cred_label(new));
173	set_cred_label(new, aa_get_newest_label(ctx->previous));
174	AA_BUG(!cred_label(new));
175	/* clear exec && prev information when restoring to previous context */
176	aa_clear_task_ctx_trans(ctx);
177
178	commit_creds(new);
179
180	return 0;
181}
182
183/**
184 * audit_ptrace_mask - convert mask to permission string
185 * @mask: permission mask to convert
186 *
187 * Returns: pointer to static string
188 */
189static const char *audit_ptrace_mask(u32 mask)
190{
191	switch (mask) {
192	case MAY_READ:
193		return "read";
194	case MAY_WRITE:
195		return "trace";
196	case AA_MAY_BE_READ:
197		return "readby";
198	case AA_MAY_BE_TRACED:
199		return "tracedby";
200	}
201	return "";
202}
203
204/* call back to audit ptrace fields */
205static void audit_ptrace_cb(struct audit_buffer *ab, void *va)
206{
207	struct common_audit_data *sa = va;
208	struct apparmor_audit_data *ad = aad(sa);
209
210	if (ad->request & AA_PTRACE_PERM_MASK) {
211		audit_log_format(ab, " requested_mask=\"%s\"",
212				 audit_ptrace_mask(ad->request));
213
214		if (ad->denied & AA_PTRACE_PERM_MASK) {
215			audit_log_format(ab, " denied_mask=\"%s\"",
216					 audit_ptrace_mask(ad->denied));
217		}
218	}
219	audit_log_format(ab, " peer=");
220	aa_label_xaudit(ab, labels_ns(ad->subj_label), ad->peer,
221			FLAGS_NONE, GFP_ATOMIC);
222}
223
224/* assumes check for RULE_MEDIATES is already done */
225/* TODO: conditionals */
226static int profile_ptrace_perm(const struct cred *cred,
227			       struct aa_profile *profile,
228			       struct aa_label *peer, u32 request,
229			       struct apparmor_audit_data *ad)
230{
231	struct aa_ruleset *rules = profile->label.rules[0];
232	struct aa_perms perms = { };
233
234	ad->subj_cred = cred;
235	ad->peer = peer;
236	aa_profile_match_label(profile, rules, peer, AA_CLASS_PTRACE, request,
237			       &perms);
238	aa_apply_modes_to_perms(profile, &perms);
239	return aa_check_perms(profile, &perms, request, ad, audit_ptrace_cb);
240}
241
242static int profile_tracee_perm(const struct cred *cred,
243			       struct aa_profile *tracee,
244			       struct aa_label *tracer, u32 request,
245			       struct apparmor_audit_data *ad)
246{
247	if (profile_unconfined(tracee) || unconfined(tracer) ||
248	    !label_mediates(&tracee->label, AA_CLASS_PTRACE))
249		return 0;
250
251	return profile_ptrace_perm(cred, tracee, tracer, request, ad);
252}
253
254static int profile_tracer_perm(const struct cred *cred,
255			       struct aa_profile *tracer,
256			       struct aa_label *tracee, u32 request,
257			       struct apparmor_audit_data *ad)
258{
259	if (profile_unconfined(tracer))
260		return 0;
261
262	if (label_mediates(&tracer->label, AA_CLASS_PTRACE))
263		return profile_ptrace_perm(cred, tracer, tracee, request, ad);
264
265	/* profile uses the old style capability check for ptrace */
266	if (&tracer->label == tracee)
267		return 0;
268
269	ad->subj_label = &tracer->label;
270	ad->peer = tracee;
271	ad->request = 0;
272	ad->error = aa_capable(cred, &tracer->label, CAP_SYS_PTRACE,
273			       CAP_OPT_NONE);
274
275	return aa_audit(AUDIT_APPARMOR_AUTO, tracer, ad, audit_ptrace_cb);
276}
277
278/**
279 * aa_may_ptrace - test if tracer task can trace the tracee
280 * @tracer_cred: cred of task doing the tracing  (NOT NULL)
281 * @tracer: label of the task doing the tracing  (NOT NULL)
282 * @tracee_cred: cred of task to be traced
283 * @tracee: task label to be traced
284 * @request: permission request
285 *
286 * Returns: %0 else error code if permission denied or error
287 */
288int aa_may_ptrace(const struct cred *tracer_cred, struct aa_label *tracer,
289		  const struct cred *tracee_cred, struct aa_label *tracee,
290		  u32 request)
291{
292	struct aa_profile *profile;
293	u32 xrequest = request << PTRACE_PERM_SHIFT;
294	DEFINE_AUDIT_DATA(sa, LSM_AUDIT_DATA_NONE, AA_CLASS_PTRACE, OP_PTRACE);
295
296	return xcheck_labels(tracer, tracee, profile,
297			profile_tracer_perm(tracer_cred, profile, tracee,
298					    request, &sa),
299			profile_tracee_perm(tracee_cred, profile, tracer,
300					    xrequest, &sa));
301}
302
303/* call back to audit ptrace fields */
304static void audit_ns_cb(struct audit_buffer *ab, void *va)
305{
306	struct apparmor_audit_data *ad = aad_of_va(va);
307
308	if (ad->request & AA_USERNS_CREATE)
309		audit_log_format(ab, " requested=\"userns_create\"");
310
311	if (ad->denied & AA_USERNS_CREATE)
312		audit_log_format(ab, " denied=\"userns_create\"");
313}
314
315int aa_profile_ns_perm(struct aa_profile *profile,
316		       struct apparmor_audit_data *ad,
317		       u32 request)
318{
319	struct aa_perms perms = { };
320	int error = 0;
321
322	ad->subj_label = &profile->label;
323	ad->request = request;
324
325	if (!profile_unconfined(profile)) {
326		struct aa_ruleset *rules = profile->label.rules[0];
327		aa_state_t state;
328
329		state = RULE_MEDIATES(rules, ad->class);
330		if (!state)
331			/* TODO: add flag to complain about unmediated */
332			return 0;
333		perms = *aa_lookup_perms(rules->policy, state);
334		aa_apply_modes_to_perms(profile, &perms);
335		error = aa_check_perms(profile, &perms, request, ad,
336				       audit_ns_cb);
337	}
338
339	return error;
340}