/*
 * Creating audit events from TTY input.
 *
 * Copyright (C) 2007 Red Hat, Inc.  All rights reserved.  This copyrighted
 * material is made available to anyone wishing to use, modify, copy, or
 * redistribute it subject to the terms and conditions of the GNU General
 * Public License v.2.
 *
 * Authors: Miloslav Trmac <mitr@redhat.com>
 */

#include <linux/audit.h>
#include <linux/slab.h>
#include <linux/tty.h>

struct tty_audit_buf {
        struct mutex mutex;     /* Protects all data below */
        dev_t dev;              /* The TTY which the data is from */
        unsigned icanon:1;
        size_t valid;
        unsigned char *data;    /* Allocated size N_TTY_BUF_SIZE */
};

static struct tty_audit_buf *tty_audit_buf_ref(void)
{
        struct tty_audit_buf *buf;

        buf = current->signal->tty_audit_buf;
        WARN_ON(buf == ERR_PTR(-ESRCH));
        return buf;
}

static struct tty_audit_buf *tty_audit_buf_alloc(void)
{
        struct tty_audit_buf *buf;

        buf = kmalloc(sizeof(*buf), GFP_KERNEL);
        if (!buf)
                goto err;
        buf->data = kmalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
        if (!buf->data)
                goto err_buf;
        mutex_init(&buf->mutex);
        buf->dev = MKDEV(0, 0);
        buf->icanon = 0;
        buf->valid = 0;
        return buf;

err_buf:
        kfree(buf);
err:
        return NULL;
}

static void tty_audit_buf_free(struct tty_audit_buf *buf)
{
        WARN_ON(buf->valid != 0);
        kfree(buf->data);
        kfree(buf);
}

static void tty_audit_log(const char *description, dev_t dev,
                          unsigned char *data, size_t size)
{
        struct audit_buffer *ab;
        struct task_struct *tsk = current;
        pid_t pid = task_pid_nr(tsk);
        uid_t uid = from_kuid(&init_user_ns, task_uid(tsk));
        uid_t loginuid = from_kuid(&init_user_ns, audit_get_loginuid(tsk));
        unsigned int sessionid = audit_get_sessionid(tsk);

        ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_TTY);
        if (ab) {
                char name[sizeof(tsk->comm)];

                audit_log_format(ab, "%s pid=%u uid=%u auid=%u ses=%u major=%d"
                                 " minor=%d comm=", description, pid, uid,
                                 loginuid, sessionid, MAJOR(dev), MINOR(dev));
                get_task_comm(name, tsk);
                audit_log_untrustedstring(ab, name);
                audit_log_format(ab, " data=");
                audit_log_n_hex(ab, data, size);
                audit_log_end(ab);
        }
}

/**
 *      tty_audit_buf_push      -       Push buffered data out
 *
 *      Generate an audit message from the contents of @buf, which is owned by
 *      the current task.  @buf->mutex must be locked.
 */
static void tty_audit_buf_push(struct tty_audit_buf *buf)
{
        if (buf->valid == 0)
                return;
        if (audit_enabled == 0) {
                buf->valid = 0;
                return;
        }
        tty_audit_log("tty", buf->dev, buf->data, buf->valid);
        buf->valid = 0;
}

/**
 *      tty_audit_exit  -       Handle a task exit
 *
 *      Make sure all buffered data is written out and deallocate the buffer.
 *      Only needs to be called if current->signal->tty_audit_buf != %NULL.
 *
 *      The process is single-threaded at this point; no other threads share
 *      current->signal.
 */
void tty_audit_exit(void)
{
        struct tty_audit_buf *buf;

        buf = xchg(&current->signal->tty_audit_buf, ERR_PTR(-ESRCH));
        if (!buf)
                return;

        tty_audit_buf_push(buf);
        tty_audit_buf_free(buf);
}

/**
 *      tty_audit_fork  -       Copy TTY audit state for a new task
 *
 *      Set up TTY audit state in @sig from current.  @sig needs no locking.
 */
void tty_audit_fork(struct signal_struct *sig)
{
        sig->audit_tty = current->signal->audit_tty;
}

/**
 *      tty_audit_tiocsti       -       Log TIOCSTI
 */
void tty_audit_tiocsti(struct tty_struct *tty, char ch)
{
        dev_t dev;

        dev = MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
        if (tty_audit_push())
                return;

        if (audit_enabled)
                tty_audit_log("ioctl=TIOCSTI", dev, &ch, 1);
}

/**
 *      tty_audit_push  -       Flush current's pending audit data
 *
 *      Returns 0 if success, -EPERM if tty audit is disabled
 */
int tty_audit_push(void)
{
        struct tty_audit_buf *buf;

        if (~current->signal->audit_tty & AUDIT_TTY_ENABLE)
                return -EPERM;

        buf = tty_audit_buf_ref();
        if (!IS_ERR_OR_NULL(buf)) {
                mutex_lock(&buf->mutex);
                tty_audit_buf_push(buf);
                mutex_unlock(&buf->mutex);
        }
        return 0;
}

/**
 *      tty_audit_buf_get       -       Get an audit buffer.
 *
 *      Get an audit buffer, allocate it if necessary.  Return %NULL
 *      if out of memory or ERR_PTR(-ESRCH) if tty_audit_exit() has already
 *      occurred.  Otherwise, return a new reference to the buffer.
 */
static struct tty_audit_buf *tty_audit_buf_get(void)
{
        struct tty_audit_buf *buf;

        buf = tty_audit_buf_ref();
        if (buf)
                return buf;

        buf = tty_audit_buf_alloc();
        if (buf == NULL) {
                audit_log_lost("out of memory in TTY auditing");
                return NULL;
        }

        /* Race to use this buffer, free it if another wins */
        if (cmpxchg(&current->signal->tty_audit_buf, NULL, buf) != NULL)
                tty_audit_buf_free(buf);
        return tty_audit_buf_ref();
}

/**
 *      tty_audit_add_data      -       Add data for TTY auditing.
 *
 *      Audit @data of @size from @tty, if necessary.
 */
void tty_audit_add_data(struct tty_struct *tty, const void *data, size_t size)
{
        struct tty_audit_buf *buf;
        unsigned int icanon = !!L_ICANON(tty);
        unsigned int audit_tty;
        dev_t dev;

        audit_tty = READ_ONCE(current->signal->audit_tty);
        if (~audit_tty & AUDIT_TTY_ENABLE)
                return;

        if (unlikely(size == 0))
                return;

        if (tty->driver->type == TTY_DRIVER_TYPE_PTY
            && tty->driver->subtype == PTY_TYPE_MASTER)
                return;

        if ((~audit_tty & AUDIT_TTY_LOG_PASSWD) && icanon && !L_ECHO(tty))
                return;

        buf = tty_audit_buf_get();
        if (IS_ERR_OR_NULL(buf))
                return;

        mutex_lock(&buf->mutex);
        dev = MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
        if (buf->dev != dev || buf->icanon != icanon) {
                tty_audit_buf_push(buf);
                buf->dev = dev;
                buf->icanon = icanon;
        }
        do {
                size_t run;

                run = N_TTY_BUF_SIZE - buf->valid;
                if (run > size)
                        run = size;
                memcpy(buf->data + buf->valid, data, run);
                buf->valid += run;
                data += run;
                size -= run;
                if (buf->valid == N_TTY_BUF_SIZE)
                        tty_audit_buf_push(buf);
        } while (size != 0);
        mutex_unlock(&buf->mutex);
}