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tty_audit.c

/*
 * 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/file.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;
      if (PAGE_SIZE != N_TTY_BUF_SIZE)
            buf->data = kmalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
      else
            buf->data = (unsigned char *)__get_free_page(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);
      if (PAGE_SIZE != N_TTY_BUF_SIZE)
            kfree(buf->data);
      else
            free_page((unsigned long)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);
}

/**
 *    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, uid_t loginuid,
                         struct tty_audit_buf *buf)
{
      struct audit_buffer *ab;

      if (buf->valid == 0)
            return;
      if (audit_enabled == 0)
            return;
      ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_TTY);
      if (ab) {
            char name[sizeof(tsk->comm)];

            audit_log_format(ab, "tty pid=%u uid=%u auid=%u major=%d "
                         "minor=%d comm=", tsk->pid, tsk->uid,
                         loginuid, buf->major, buf->minor);
            get_task_comm(name, tsk);
            audit_log_untrustedstring(ab, name);
            audit_log_format(ab, " data=");
            audit_log_n_untrustedstring(ab, buf->valid, buf->data);
            audit_log_end(ab);
      }
      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)
{
      tty_audit_buf_push(current, audit_get_loginuid(current->audit_context),
                     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);
      sig->tty_audit_buf = NULL;
}

/**
 *    tty_audit_push_task     -     Flush task's pending audit data
 */
void tty_audit_push_task(struct task_struct *tsk, uid_t loginuid)
{
      struct tty_audit_buf *buf;

      spin_lock_irq(&tsk->sighand->siglock);
      buf = tsk->signal->tty_audit_buf;
      if (buf)
            atomic_inc(&buf->count);
      spin_unlock_irq(&tsk->sighand->siglock);
      if (!buf)
            return;

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

      tty_audit_buf_put(buf);
}

/**
 *    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;

      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);
      }
}

/**
 *    tty_audit_opening -     A TTY is being opened.
 *
 *    As a special hack, tasks that close all their TTYs and open new ones
 *    are assumed to be system daemons (e.g. getty) and auditing is
 *    automatically disabled for them.
 */
void tty_audit_opening(void)
{
      int disable;

      disable = 1;
      spin_lock_irq(&current->sighand->siglock);
      if (current->signal->audit_tty == 0)
            disable = 0;
      spin_unlock_irq(&current->sighand->siglock);
      if (!disable)
            return;

      task_lock(current);
      if (current->files) {
            struct fdtable *fdt;
            unsigned i;

            /*
             * We don't take a ref to the file, so we must hold ->file_lock
             * instead.
             */
            spin_lock(&current->files->file_lock);
            fdt = files_fdtable(current->files);
            for (i = 0; i < fdt->max_fds; i++) {
                  struct file *filp;

                  filp = fcheck_files(current->files, i);
                  if (filp && is_tty(filp)) {
                        disable = 0;
                        break;
                  }
            }
            spin_unlock(&current->files->file_lock);
      }
      task_unlock(current);
      if (!disable)
            return;

      spin_lock_irq(&current->sighand->siglock);
      current->signal->audit_tty = 0;
      spin_unlock_irq(&current->sighand->siglock);
}

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