tty_audit.c

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/*
 * 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 <[email protected]>
 */

#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);
    }
}

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;
}

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);
}

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);
}

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);
}

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);
    }
}

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;
}

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;
}

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);
}

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);
    }
}