drivers/tty/tty_audit.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Creating audit events from TTY input.
   4  *
   5  * Copyright (C) 2007 Red Hat, Inc.  All rights reserved.
   6  *
   7  * Authors: Miloslav Trmac <mitr@redhat.com>
   8  */
   9
  10 #include <linux/audit.h>
  11 #include <linux/slab.h>
  12 #include <linux/tty.h>
  13 #include "tty.h"
  14
  15 struct tty_audit_buf {
  16         struct mutex mutex;     /* Protects all data below */
  17         dev_t dev;              /* The TTY which the data is from */
  18         bool icanon;
  19         size_t valid;
  20         u8 *data;               /* Allocated size N_TTY_BUF_SIZE */
  21 };
  22
  23 static struct tty_audit_buf *tty_audit_buf_ref(void)
  24 {
  25         struct tty_audit_buf *buf;
  26
  27         buf = current->signal->tty_audit_buf;
  28         WARN_ON(buf == ERR_PTR(-ESRCH));
  29         return buf;
  30 }
  31
  32 static struct tty_audit_buf *tty_audit_buf_alloc(void)
  33 {
  34         struct tty_audit_buf *buf;
  35
  36         buf = kzalloc(sizeof(*buf), GFP_KERNEL);
  37         if (!buf)
  38                 goto err;
  39
  40         buf->data = kmalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
  41         if (!buf->data)
  42                 goto err_buf;
  43
  44         mutex_init(&buf->mutex);
  45
  46         return buf;
  47
  48 err_buf:
  49         kfree(buf);
  50 err:
  51         return NULL;
  52 }
  53
  54 static void tty_audit_buf_free(struct tty_audit_buf *buf)
  55 {
  56         WARN_ON(buf->valid != 0);
  57         kfree(buf->data);
  58         kfree(buf);
  59 }
  60
  61 static void tty_audit_log(const char *description, dev_t dev,
  62                           const u8 *data, size_t size)
  63 {
  64         struct audit_buffer *ab;
  65         pid_t pid = task_pid_nr(current);
  66         uid_t uid = from_kuid(&init_user_ns, task_uid(current));
  67         uid_t loginuid = from_kuid(&init_user_ns, audit_get_loginuid(current));
  68         unsigned int sessionid = audit_get_sessionid(current);
  69         char name[TASK_COMM_LEN];
  70
  71         ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_TTY);
  72         if (!ab)
  73                 return;
  74
  75         audit_log_format(ab, "%s pid=%u uid=%u auid=%u ses=%u major=%d minor=%d comm=",
  76                          description, pid, uid, loginuid, sessionid,
  77                          MAJOR(dev), MINOR(dev));
  78         get_task_comm(name, current);
  79         audit_log_untrustedstring(ab, name);
  80         audit_log_format(ab, " data=");
  81         audit_log_n_hex(ab, data, size);
  82         audit_log_end(ab);
  83 }
  84
  85 /*
  86  *      tty_audit_buf_push      -       Push buffered data out
  87  *
  88  *      Generate an audit message from the contents of @buf, which is owned by
  89  *      the current task.  @buf->mutex must be locked.
  90  */
  91 static void tty_audit_buf_push(struct tty_audit_buf *buf)
  92 {
  93         if (buf->valid == 0)
  94                 return;
  95         if (audit_enabled == AUDIT_OFF) {
  96                 buf->valid = 0;
  97                 return;
  98         }
  99         tty_audit_log("tty", buf->dev, buf->data, buf->valid);
 100         buf->valid = 0;
 101 }
 102
 103 /**
 104  *      tty_audit_exit  -       Handle a task exit
 105  *
 106  *      Make sure all buffered data is written out and deallocate the buffer.
 107  *      Only needs to be called if current->signal->tty_audit_buf != %NULL.
 108  *
 109  *      The process is single-threaded at this point; no other threads share
 110  *      current->signal.
 111  */
 112 void tty_audit_exit(void)
 113 {
 114         struct tty_audit_buf *buf;
 115
 116         buf = xchg(&current->signal->tty_audit_buf, ERR_PTR(-ESRCH));
 117         if (!buf)
 118                 return;
 119
 120         tty_audit_buf_push(buf);
 121         tty_audit_buf_free(buf);
 122 }
 123
 124 /*
 125  *      tty_audit_fork  -       Copy TTY audit state for a new task
 126  *
 127  *      Set up TTY audit state in @sig from current.  @sig needs no locking.
 128  */
 129 void tty_audit_fork(struct signal_struct *sig)
 130 {
 131         sig->audit_tty = current->signal->audit_tty;
 132 }
 133
 134 /*
 135  *      tty_audit_tiocsti       -       Log TIOCSTI
 136  */
 137 void tty_audit_tiocsti(const struct tty_struct *tty, u8 ch)
 138 {
 139         dev_t dev;
 140
 141         dev = MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
 142         if (tty_audit_push())
 143                 return;
 144
 145         if (audit_enabled)
 146                 tty_audit_log("ioctl=TIOCSTI", dev, &ch, 1);
 147 }
 148
 149 /*
 150  *      tty_audit_push  -       Flush current's pending audit data
 151  *
 152  *      Returns 0 if success, -EPERM if tty audit is disabled
 153  */
 154 int tty_audit_push(void)
 155 {
 156         struct tty_audit_buf *buf;
 157
 158         if (~current->signal->audit_tty & AUDIT_TTY_ENABLE)
 159                 return -EPERM;
 160
 161         buf = tty_audit_buf_ref();
 162         if (!IS_ERR_OR_NULL(buf)) {
 163                 mutex_lock(&buf->mutex);
 164                 tty_audit_buf_push(buf);
 165                 mutex_unlock(&buf->mutex);
 166         }
 167         return 0;
 168 }
 169
 170 /*
 171  *      tty_audit_buf_get       -       Get an audit buffer.
 172  *
 173  *      Get an audit buffer, allocate it if necessary.  Return %NULL
 174  *      if out of memory or ERR_PTR(-ESRCH) if tty_audit_exit() has already
 175  *      occurred.  Otherwise, return a new reference to the buffer.
 176  */
 177 static struct tty_audit_buf *tty_audit_buf_get(void)
 178 {
 179         struct tty_audit_buf *buf;
 180
 181         buf = tty_audit_buf_ref();
 182         if (buf)
 183                 return buf;
 184
 185         buf = tty_audit_buf_alloc();
 186         if (buf == NULL) {
 187                 audit_log_lost("out of memory in TTY auditing");
 188                 return NULL;
 189         }
 190
 191         /* Race to use this buffer, free it if another wins */
 192         if (cmpxchg(&current->signal->tty_audit_buf, NULL, buf) != NULL)
 193                 tty_audit_buf_free(buf);
 194         return tty_audit_buf_ref();
 195 }
 196
 197 /*
 198  *      tty_audit_add_data      -       Add data for TTY auditing.
 199  *
 200  *      Audit @data of @size from @tty, if necessary.
 201  */
 202 void tty_audit_add_data(const struct tty_struct *tty, const void *data,
 203                         size_t size)
 204 {
 205         struct tty_audit_buf *buf;
 206         unsigned int audit_tty;
 207         bool icanon = L_ICANON(tty);
 208         dev_t dev;
 209
 210         audit_tty = READ_ONCE(current->signal->audit_tty);
 211         if (~audit_tty & AUDIT_TTY_ENABLE)
 212                 return;
 213
 214         if (unlikely(size == 0))
 215                 return;
 216
 217         if (tty->driver->type == TTY_DRIVER_TYPE_PTY
 218             && tty->driver->subtype == PTY_TYPE_MASTER)
 219                 return;
 220
 221         if ((~audit_tty & AUDIT_TTY_LOG_PASSWD) && icanon && !L_ECHO(tty))
 222                 return;
 223
 224         buf = tty_audit_buf_get();
 225         if (IS_ERR_OR_NULL(buf))
 226                 return;
 227
 228         mutex_lock(&buf->mutex);
 229         dev = MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
 230         if (buf->dev != dev || buf->icanon != icanon) {
 231                 tty_audit_buf_push(buf);
 232                 buf->dev = dev;
 233                 buf->icanon = icanon;
 234         }
 235         do {
 236                 size_t run;
 237
 238                 run = N_TTY_BUF_SIZE - buf->valid;
 239                 if (run > size)
 240                         run = size;
 241                 memcpy(buf->data + buf->valid, data, run);
 242                 buf->valid += run;
 243                 data += run;
 244                 size -= run;
 245                 if (buf->valid == N_TTY_BUF_SIZE)
 246                         tty_audit_buf_push(buf);
 247         } while (size != 0);
 248         mutex_unlock(&buf->mutex);
 249 }