linux/security/apparmor/task.c
John Johansen fa9b63adab apparmor: add user namespace creation mediation
Unprivileged user namespace creation is often used as a first step
in privilege escalation attacks. Instead of disabling it at the
sysrq level, which blocks its legitimate use as for setting up a sandbox,
allow control on a per domain basis.

This allows an admin to quickly lock down a system while also still
allowing legitimate use.

Reviewed-by: Georgia Garcia <georgia.garcia@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>
2023-10-18 15:49:02 -07:00

342 lines
8.6 KiB
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_unconfined(tracee) || unconfined(tracer) ||
!ANY_RULE_MEDIATES(&tracee->rules, 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_unconfined(tracer))
return 0;
if (ANY_RULE_MEDIATES(&tracer->rules, 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)
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: label of the task doing the tracing (NOT NULL)
* @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\"");
}
int aa_profile_ns_perm(struct aa_profile *profile,
struct apparmor_audit_data *ad,
u32 request)
{
struct aa_perms perms = { };
int error = 0;
ad->subj_label = &profile->label;
ad->request = request;
if (!profile_unconfined(profile)) {
struct aa_ruleset *rules = list_first_entry(&profile->rules,
typeof(*rules),
list);
aa_state_t state;
state = RULE_MEDIATES(rules, ad->class);
if (!state)
/* TODO: add flag to complain about unmediated */
return 0;
perms = *aa_lookup_perms(rules->policy, state);
aa_apply_modes_to_perms(profile, &perms);
error = aa_check_perms(profile, &perms, request, ad,
audit_ns_cb);
}
return error;
}