// 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/path.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 = profile->label.rules[0];
        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) ||
            !label_mediates(&tracee->label, 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 (label_mediates(&tracer->label, 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_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));
}

static const char *get_current_exe_path(char *buffer, int buffer_size)
{
        struct file *exe_file;
        struct path p;
        const char *path_str;

        exe_file = get_task_exe_file(current);
        if (!exe_file)
                return ERR_PTR(-ENOENT);
        p = exe_file->f_path;
        path_get(&p);

        if (aa_path_name(&p, FLAG_VIEW_SUBNS, buffer, &path_str, NULL, NULL))
                return ERR_PTR(-ENOMEM);

        fput(exe_file);
        path_put(&p);

        return path_str;
}

/* 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);
        char *buffer;
        const char *path;

        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\"");

        buffer = aa_get_buffer(false);
        if (!buffer)
                return; // OOM
        path = get_current_exe_path(buffer, aa_g_path_max);
        if (!IS_ERR(path))
                audit_log_format(ab, " execpath=\"%s\"", path);
        aa_put_buffer(buffer);
}

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 = profile->label.rules[0];
                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;
}