/*
 * 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 {
        atomic_t count;
        struct mutex mutex;     /* Protects all data below */
        int major, minor;       /* 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_alloc(int major, int minor,
                                                 int icanon)
{
        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;
        atomic_set(&buf->count, 1);
        mutex_init(&buf->mutex);
        buf->major = major;
        buf->minor = minor;
        buf->icanon = icanon;
        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_buf_put(struct tty_audit_buf *buf)
{
        if (atomic_dec_and_test(&buf->count))
                tty_audit_buf_free(buf);
}

static void tty_audit_log(const char *description, struct task_struct *tsk,
                          kuid_t loginuid, unsigned sessionid, int major,
                          int minor, unsigned char *data, size_t size)
{
        struct audit_buffer *ab;

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

                audit_log_format(ab, "%s pid=%u uid=%u auid=%u ses=%u "
                                 "major=%d minor=%d comm=", description,
                                 tsk->pid,
                                 from_kuid(&init_user_ns, uid),
                                 from_kuid(&init_user_ns, loginuid),
                                 sessionid,
                                 major, minor);
                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
 *      @tsk with @loginuid.  @buf->mutex must be locked.
 */
static void tty_audit_buf_push(struct task_struct *tsk, kuid_t loginuid,
                               unsigned int sessionid,
                               struct tty_audit_buf *buf)
{
        if (buf->valid == 0)
                return;
        if (audit_enabled == 0) {
                buf->valid = 0;
                return;
        }
        tty_audit_log("tty", tsk, loginuid, sessionid, buf->major, buf->minor,
                      buf->data, buf->valid);
        buf->valid = 0;
}

/**
 *      tty_audit_buf_push_current      -       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_current(struct tty_audit_buf *buf)
{
        kuid_t auid = audit_get_loginuid(current);
        unsigned int sessionid = audit_get_sessionid(current);
        tty_audit_buf_push(current, auid, sessionid, buf);
}

/**
 *      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.
 */
void tty_audit_exit(void)
{
        struct tty_audit_buf *buf;

        spin_lock_irq(&current->sighand->siglock);
        buf = current->signal->tty_audit_buf;
        current->signal->tty_audit_buf = NULL;
        spin_unlock_irq(&current->sighand->siglock);
        if (!buf)
                return;

        mutex_lock(&buf->mutex);
        tty_audit_buf_push_current(buf);
        mutex_unlock(&buf->mutex);

        tty_audit_buf_put(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)
{
        spin_lock_irq(&current->sighand->siglock);
        sig->audit_tty = current->signal->audit_tty;
        spin_unlock_irq(&current->sighand->siglock);
}

/**
 *      tty_audit_tiocsti       -       Log TIOCSTI
 */
void tty_audit_tiocsti(struct tty_struct *tty, char ch)
{
        struct tty_audit_buf *buf;
        int major, minor, should_audit;

        spin_lock_irq(&current->sighand->siglock);
        should_audit = current->signal->audit_tty;
        buf = current->signal->tty_audit_buf;
        if (buf)
                atomic_inc(&buf->count);
        spin_unlock_irq(&current->sighand->siglock);

        major = tty->driver->major;
        minor = tty->driver->minor_start + tty->index;
        if (buf) {
                mutex_lock(&buf->mutex);
                if (buf->major == major && buf->minor == minor)
                        tty_audit_buf_push_current(buf);
                mutex_unlock(&buf->mutex);
                tty_audit_buf_put(buf);
        }

        if (should_audit && audit_enabled) {
                kuid_t auid;
                unsigned int sessionid;

                auid = audit_get_loginuid(current);
                sessionid = audit_get_sessionid(current);
                tty_audit_log("ioctl=TIOCSTI", current, auid, sessionid, major,
                              minor, &ch, 1);
        }
}

/**
 * tty_audit_push_task  -       Flush task's pending audit data
 * @tsk:                task pointer
 * @loginuid:           sender login uid
 * @sessionid:          sender session id
 *
 * Called with a ref on @tsk held. Try to lock sighand and get a
 * reference to the tty audit buffer if available.
 * Flush the buffer or return an appropriate error code.
 */
int tty_audit_push_task(struct task_struct *tsk, kuid_t loginuid, u32 sessionid)
{
        struct tty_audit_buf *buf = ERR_PTR(-EPERM);
        unsigned long flags;

        if (!lock_task_sighand(tsk, &flags))
                return -ESRCH;

        if (tsk->signal->audit_tty) {
                buf = tsk->signal->tty_audit_buf;
                if (buf)
                        atomic_inc(&buf->count);
        }
        unlock_task_sighand(tsk, &flags);

        /*
         * Return 0 when signal->audit_tty set
         * but tsk->signal->tty_audit_buf == NULL.
         */
        if (!buf || IS_ERR(buf))
                return PTR_ERR(buf);

        mutex_lock(&buf->mutex);
        tty_audit_buf_push(tsk, loginuid, sessionid, buf);
        mutex_unlock(&buf->mutex);

        tty_audit_buf_put(buf);
        return 0;
}

/**
 *      tty_audit_buf_get       -       Get an audit buffer.
 *
 *      Get an audit buffer for @tty, allocate it if necessary.  Return %NULL
 *      if TTY auditing is disabled or out of memory.  Otherwise, return a new
 *      reference to the buffer.
 */
static struct tty_audit_buf *tty_audit_buf_get(struct tty_struct *tty)
{
        struct tty_audit_buf *buf, *buf2;

        buf = NULL;
        buf2 = NULL;
        spin_lock_irq(&current->sighand->siglock);
        if (likely(!current->signal->audit_tty))
                goto out;
        buf = current->signal->tty_audit_buf;
        if (buf) {
                atomic_inc(&buf->count);
                goto out;
        }
        spin_unlock_irq(&current->sighand->siglock);

        buf2 = tty_audit_buf_alloc(tty->driver->major,
                                   tty->driver->minor_start + tty->index,
                                   tty->icanon);
        if (buf2 == NULL) {
                audit_log_lost("out of memory in TTY auditing");
                return NULL;
        }

        spin_lock_irq(&current->sighand->siglock);
        if (!current->signal->audit_tty)
                goto out;
        buf = current->signal->tty_audit_buf;
        if (!buf) {
                current->signal->tty_audit_buf = buf2;
                buf = buf2;
                buf2 = NULL;
        }
        atomic_inc(&buf->count);
        /* Fall through */
 out:
        spin_unlock_irq(&current->sighand->siglock);
        if (buf2)
                tty_audit_buf_free(buf2);
        return buf;
}

/**
 *      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, unsigned char *data,
                        size_t size)
{
        struct tty_audit_buf *buf;
        int major, minor;

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

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

        buf = tty_audit_buf_get(tty);
        if (!buf)
                return;

        mutex_lock(&buf->mutex);
        major = tty->driver->major;
        minor = tty->driver->minor_start + tty->index;
        if (buf->major != major || buf->minor != minor
            || buf->icanon != tty->icanon) {
                tty_audit_buf_push_current(buf);
                buf->major = major;
                buf->minor = minor;
                buf->icanon = tty->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_current(buf);
        } while (size != 0);
        mutex_unlock(&buf->mutex);
        tty_audit_buf_put(buf);
}

/**
 *      tty_audit_push  -       Push buffered data out
 *
 *      Make sure no audit data is pending for @tty on the current process.
 */
void tty_audit_push(struct tty_struct *tty)
{
        struct tty_audit_buf *buf;

        spin_lock_irq(&current->sighand->siglock);
        if (likely(!current->signal->audit_tty)) {
                spin_unlock_irq(&current->sighand->siglock);
                return;
        }
        buf = current->signal->tty_audit_buf;
        if (buf)
                atomic_inc(&buf->count);
        spin_unlock_irq(&current->sighand->siglock);

        if (buf) {
                int major, minor;

                major = tty->driver->major;
                minor = tty->driver->minor_start + tty->index;
                mutex_lock(&buf->mutex);
                if (buf->major == major && buf->minor == minor)
                        tty_audit_buf_push_current(buf);
                mutex_unlock(&buf->mutex);
                tty_audit_buf_put(buf);
        }
}