drivers/tty/tty_audit.c

   1 /*
   2  * Creating audit events from TTY input.
   3  *
   4  * Copyright (C) 2007 Red Hat, Inc.  All rights reserved.  This copyrighted
   5  * material is made available to anyone wishing to use, modify, copy, or
   6  * redistribute it subject to the terms and conditions of the GNU General
   7  * Public License v.2.
   8  *
   9  * Authors: Miloslav Trmac <mitr@redhat.com>
  10  */
  11
  12 #include <linux/audit.h>
  13 #include <linux/slab.h>
  14 #include <linux/tty.h>
  15
  16 struct tty_audit_buf {
  17         struct mutex mutex;     /* Protects all data below */
  18         dev_t dev;              /* The TTY which the data is from */
  19         unsigned icanon:1;
  20         size_t valid;
  21         unsigned char *data;    /* Allocated size N_TTY_BUF_SIZE */
  22 };
  23
  24 static struct tty_audit_buf *tty_audit_buf_ref(void)
  25 {
  26         struct tty_audit_buf *buf;
  27
  28         buf = current->signal->tty_audit_buf;
  29         WARN_ON(buf == ERR_PTR(-ESRCH));
  30         return buf;
  31 }
  32
  33 static struct tty_audit_buf *tty_audit_buf_alloc(void)
  34 {
  35         struct tty_audit_buf *buf;
  36
  37         buf = kmalloc(sizeof(*buf), GFP_KERNEL);
  38         if (!buf)
  39                 goto err;
  40         buf->data = kmalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
  41         if (!buf->data)
  42                 goto err_buf;
  43         mutex_init(&buf->mutex);
  44         buf->dev = MKDEV(0, 0);
  45         buf->icanon = 0;
  46         buf->valid = 0;
  47         return buf;
  48
  49 err_buf:
  50         kfree(buf);
  51 err:
  52         return NULL;
  53 }
  54
  55 static void tty_audit_buf_free(struct tty_audit_buf *buf)
  56 {
  57         WARN_ON(buf->valid != 0);
  58         kfree(buf->data);
  59         kfree(buf);
  60 }
  61
  62 static void tty_audit_log(const char *description, dev_t dev,
  63                           unsigned char *data, size_t size)
  64 {
  65         struct audit_buffer *ab;
  66         struct task_struct *tsk = current;
  67         pid_t pid = task_pid_nr(tsk);
  68         uid_t uid = from_kuid(&init_user_ns, task_uid(tsk));
  69         uid_t loginuid = from_kuid(&init_user_ns, audit_get_loginuid(tsk));
  70         unsigned int sessionid = audit_get_sessionid(tsk);
  71
  72         ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_TTY);
  73         if (ab) {
  74                 char name[sizeof(tsk->comm)];
  75
  76                 audit_log_format(ab, "%s pid=%u uid=%u auid=%u ses=%u major=%d"
  77                                  " minor=%d comm=", description, pid, uid,
  78                                  loginuid, sessionid, MAJOR(dev), MINOR(dev));
  79                 get_task_comm(name, tsk);
  80                 audit_log_untrustedstring(ab, name);
  81                 audit_log_format(ab, " data=");
  82                 audit_log_n_hex(ab, data, size);
  83                 audit_log_end(ab);
  84         }
  85 }
  86
  87 /**
  88  *      tty_audit_buf_push      -       Push buffered data out
  89  *
  90  *      Generate an audit message from the contents of @buf, which is owned by
  91  *      the current task.  @buf->mutex must be locked.
  92  */
  93 static void tty_audit_buf_push(struct tty_audit_buf *buf)
  94 {
  95         if (buf->valid == 0)
  96                 return;
  97         if (audit_enabled == 0) {
  98                 buf->valid = 0;
  99                 return;
 100         }
 101         tty_audit_log("tty", buf->dev, buf->data, buf->valid);
 102         buf->valid = 0;
 103 }
 104
 105 /**
 106  *      tty_audit_exit  -       Handle a task exit
 107  *
 108  *      Make sure all buffered data is written out and deallocate the buffer.
 109  *      Only needs to be called if current->signal->tty_audit_buf != %NULL.
 110  *
 111  *      The process is single-threaded at this point; no other threads share
 112  *      current->signal.
 113  */
 114 void tty_audit_exit(void)
 115 {
 116         struct tty_audit_buf *buf;
 117
 118         buf = xchg(&current->signal->tty_audit_buf, ERR_PTR(-ESRCH));
 119         if (!buf)
 120                 return;
 121
 122         tty_audit_buf_push(buf);
 123         tty_audit_buf_free(buf);
 124 }
 125
 126 /**
 127  *      tty_audit_fork  -       Copy TTY audit state for a new task
 128  *
 129  *      Set up TTY audit state in @sig from current.  @sig needs no locking.
 130  */
 131 void tty_audit_fork(struct signal_struct *sig)
 132 {
 133         sig->audit_tty = current->signal->audit_tty;
 134 }
 135
 136 /**
 137  *      tty_audit_tiocsti       -       Log TIOCSTI
 138  */
 139 void tty_audit_tiocsti(struct tty_struct *tty, char ch)
 140 {
 141         dev_t dev;
 142
 143         dev = MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
 144         if (tty_audit_push())
 145                 return;
 146
 147         if (audit_enabled)
 148                 tty_audit_log("ioctl=TIOCSTI", dev, &ch, 1);
 149 }
 150
 151 /**
 152  *      tty_audit_push  -       Flush current's pending audit data
 153  *
 154  *      Returns 0 if success, -EPERM if tty audit is disabled
 155  */
 156 int tty_audit_push(void)
 157 {
 158         struct tty_audit_buf *buf;
 159
 160         if (~current->signal->audit_tty & AUDIT_TTY_ENABLE)
 161                 return -EPERM;
 162
 163         buf = tty_audit_buf_ref();
 164         if (!IS_ERR_OR_NULL(buf)) {
 165                 mutex_lock(&buf->mutex);
 166                 tty_audit_buf_push(buf);
 167                 mutex_unlock(&buf->mutex);
 168         }
 169         return 0;
 170 }
 171
 172 /**
 173  *      tty_audit_buf_get       -       Get an audit buffer.
 174  *
 175  *      Get an audit buffer, allocate it if necessary.  Return %NULL
 176  *      if out of memory or ERR_PTR(-ESRCH) if tty_audit_exit() has already
 177  *      occurred.  Otherwise, return a new reference to the buffer.
 178  */
 179 static struct tty_audit_buf *tty_audit_buf_get(void)
 180 {
 181         struct tty_audit_buf *buf;
 182
 183         buf = tty_audit_buf_ref();
 184         if (buf)
 185                 return buf;
 186
 187         buf = tty_audit_buf_alloc();
 188         if (buf == NULL) {
 189                 audit_log_lost("out of memory in TTY auditing");
 190                 return NULL;
 191         }
 192
 193         /* Race to use this buffer, free it if another wins */
 194         if (cmpxchg(&current->signal->tty_audit_buf, NULL, buf) != NULL)
 195                 tty_audit_buf_free(buf);
 196         return tty_audit_buf_ref();
 197 }
 198
 199 /**
 200  *      tty_audit_add_data      -       Add data for TTY auditing.
 201  *
 202  *      Audit @data of @size from @tty, if necessary.
 203  */
 204 void tty_audit_add_data(struct tty_struct *tty, const void *data, size_t size)
 205 {
 206         struct tty_audit_buf *buf;
 207         unsigned int icanon = !!L_ICANON(tty);
 208         unsigned int audit_tty;
 209         dev_t dev;
 210
 211         audit_tty = READ_ONCE(current->signal->audit_tty);
 212         if (~audit_tty & AUDIT_TTY_ENABLE)
 213                 return;
 214
 215         if (unlikely(size == 0))
 216                 return;
 217
 218         if (tty->driver->type == TTY_DRIVER_TYPE_PTY
 219             && tty->driver->subtype == PTY_TYPE_MASTER)
 220                 return;
 221
 222         if ((~audit_tty & AUDIT_TTY_LOG_PASSWD) && icanon && !L_ECHO(tty))
 223                 return;
 224
 225         buf = tty_audit_buf_get();
 226         if (IS_ERR_OR_NULL(buf))
 227                 return;
 228
 229         mutex_lock(&buf->mutex);
 230         dev = MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
 231         if (buf->dev != dev || buf->icanon != icanon) {
 232                 tty_audit_buf_push(buf);
 233                 buf->dev = dev;
 234                 buf->icanon = icanon;
 235         }
 236         do {
 237                 size_t run;
 238
 239                 run = N_TTY_BUF_SIZE - buf->valid;
 240                 if (run > size)
 241                         run = size;
 242                 memcpy(buf->data + buf->valid, data, run);
 243                 buf->valid += run;
 244                 data += run;
 245                 size -= run;
 246                 if (buf->valid == N_TTY_BUF_SIZE)
 247                         tty_audit_buf_push(buf);
 248         } while (size != 0);
 249         mutex_unlock(&buf->mutex);
 250 }