about summary refs log tree commit diff
path: root/elf/dl-tunables.c
blob: 26e6e266120596b8041e2ce133d057f8dc7838a8 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
/* The tunable framework.  See the README.tunables to know how to use the
   tunable in a glibc module.

   Copyright (C) 2016-2020 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <startup.h>
#include <stdint.h>
#include <stdbool.h>
#include <unistd.h>
#include <stdlib.h>
#include <sysdep.h>
#include <fcntl.h>
#include <ldsodefs.h>

#define TUNABLES_INTERNAL 1
#include "dl-tunables.h"

#include <not-errno.h>

#if TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring
# define GLIBC_TUNABLES "GLIBC_TUNABLES"
#endif

#if TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring
static char *
tunables_strdup (const char *in)
{
  size_t i = 0;

  while (in[i++] != '\0');
  char *out = __sbrk (i);

  /* For most of the tunables code, we ignore user errors.  However,
     this is a system error - and running out of memory at program
     startup should be reported, so we do.  */
  if (out == (void *)-1)
    _dl_fatal_printf ("sbrk() failure while processing tunables\n");

  i--;

  while (i-- > 0)
    out[i] = in[i];

  return out;
}
#endif

static char **
get_next_env (char **envp, char **name, size_t *namelen, char **val,
	      char ***prev_envp)
{
  while (envp != NULL && *envp != NULL)
    {
      char **prev = envp;
      char *envline = *envp++;
      int len = 0;

      while (envline[len] != '\0' && envline[len] != '=')
	len++;

      /* Just the name and no value, go to the next one.  */
      if (envline[len] == '\0')
	continue;

      *name = envline;
      *namelen = len;
      *val = &envline[len + 1];
      *prev_envp = prev;

      return envp;
    }

  return NULL;
}

#define TUNABLE_SET_VAL_IF_VALID_RANGE(__cur, __val, __type)		      \
({									      \
  __type min = (__cur)->type.min;					      \
  __type max = (__cur)->type.max;					      \
									      \
  if ((__type) (__val) >= min && (__type) (__val) <= max)		      \
    {									      \
      (__cur)->val.numval = (__val);					      \
      (__cur)->initialized = true;					      \
    }									      \
})

static void
do_tunable_update_val (tunable_t *cur, const void *valp)
{
  uint64_t val;

  if (cur->type.type_code != TUNABLE_TYPE_STRING)
    val = *((int64_t *) valp);

  switch (cur->type.type_code)
    {
    case TUNABLE_TYPE_INT_32:
	{
	  TUNABLE_SET_VAL_IF_VALID_RANGE (cur, val, int64_t);
	  break;
	}
    case TUNABLE_TYPE_UINT_64:
	{
	  TUNABLE_SET_VAL_IF_VALID_RANGE (cur, val, uint64_t);
	  break;
	}
    case TUNABLE_TYPE_SIZE_T:
	{
	  TUNABLE_SET_VAL_IF_VALID_RANGE (cur, val, uint64_t);
	  break;
	}
    case TUNABLE_TYPE_STRING:
	{
	  cur->val.strval = valp;
	  break;
	}
    default:
      __builtin_unreachable ();
    }
}

/* Validate range of the input value and initialize the tunable CUR if it looks
   good.  */
static void
tunable_initialize (tunable_t *cur, const char *strval)
{
  uint64_t val;
  const void *valp;

  if (cur->type.type_code != TUNABLE_TYPE_STRING)
    {
      val = _dl_strtoul (strval, NULL);
      valp = &val;
    }
  else
    {
      cur->initialized = true;
      valp = strval;
    }
  do_tunable_update_val (cur, valp);
}

void
__tunable_set_val (tunable_id_t id, void *valp)
{
  tunable_t *cur = &tunable_list[id];

  do_tunable_update_val (cur, valp);
}

#if TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring
/* Parse the tunable string TUNESTR and adjust it to drop any tunables that may
   be unsafe for AT_SECURE processes so that it can be used as the new
   environment variable value for GLIBC_TUNABLES.  VALSTRING is the original
   environment variable string which we use to make NULL terminated values so
   that we don't have to allocate memory again for it.  */
static void
parse_tunables (char *tunestr, char *valstring)
{
  if (tunestr == NULL || *tunestr == '\0')
    return;

  char *p = tunestr;

  while (true)
    {
      char *name = p;
      size_t len = 0;

      /* First, find where the name ends.  */
      while (p[len] != '=' && p[len] != ':' && p[len] != '\0')
	len++;

      /* If we reach the end of the string before getting a valid name-value
	 pair, bail out.  */
      if (p[len] == '\0')
	return;

      /* We did not find a valid name-value pair before encountering the
	 colon.  */
      if (p[len]== ':')
	{
	  p += len + 1;
	  continue;
	}

      p += len + 1;

      /* Take the value from the valstring since we need to NULL terminate it.  */
      char *value = &valstring[p - tunestr];
      len = 0;

      while (p[len] != ':' && p[len] != '\0')
	len++;

      /* Add the tunable if it exists.  */
      for (size_t i = 0; i < sizeof (tunable_list) / sizeof (tunable_t); i++)
	{
	  tunable_t *cur = &tunable_list[i];

	  if (tunable_is_name (cur->name, name))
	    {
	      /* If we are in a secure context (AT_SECURE) then ignore the tunable
		 unless it is explicitly marked as secure.  Tunable values take
		 precedence over their envvar aliases.  */
	      if (__libc_enable_secure)
		{
		  if (cur->security_level == TUNABLE_SECLEVEL_SXID_ERASE)
		    {
		      if (p[len] == '\0')
			{
			  /* Last tunable in the valstring.  Null-terminate and
			     return.  */
			  *name = '\0';
			  return;
			}
		      else
			{
			  /* Remove the current tunable from the string.  We do
			     this by overwriting the string starting from NAME
			     (which is where the current tunable begins) with
			     the remainder of the string.  We then have P point
			     to NAME so that we continue in the correct
			     position in the valstring.  */
			  char *q = &p[len + 1];
			  p = name;
			  while (*q != '\0')
			    *name++ = *q++;
			  name[0] = '\0';
			  len = 0;
			}
		    }

		  if (cur->security_level != TUNABLE_SECLEVEL_NONE)
		    break;
		}

	      value[len] = '\0';
	      tunable_initialize (cur, value);
	      break;
	    }
	}

      if (p[len] == '\0')
	return;
      else
	p += len + 1;
    }
}
#endif

/* Enable the glibc.malloc.check tunable in SETUID/SETGID programs only when
   the system administrator has created the /etc/suid-debug file.  This is a
   special case where we want to conditionally enable/disable a tunable even
   for setuid binaries.  We use the special version of access() to avoid
   setting ERRNO, which is a TLS variable since TLS has not yet been set
   up.  */
static __always_inline void
maybe_enable_malloc_check (void)
{
  tunable_id_t id = TUNABLE_ENUM_NAME (glibc, malloc, check);
  if (__libc_enable_secure && __access_noerrno ("/etc/suid-debug", F_OK) == 0)
    tunable_list[id].security_level = TUNABLE_SECLEVEL_NONE;
}

/* Initialize the tunables list from the environment.  For now we only use the
   ENV_ALIAS to find values.  Later we will also use the tunable names to find
   values.  */
void
__tunables_init (char **envp)
{
  char *envname = NULL;
  char *envval = NULL;
  size_t len = 0;
  char **prev_envp = envp;

  maybe_enable_malloc_check ();

  while ((envp = get_next_env (envp, &envname, &len, &envval,
			       &prev_envp)) != NULL)
    {
#if TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring
      if (tunable_is_name (GLIBC_TUNABLES, envname))
	{
	  char *new_env = tunables_strdup (envname);
	  if (new_env != NULL)
	    parse_tunables (new_env + len + 1, envval);
	  /* Put in the updated envval.  */
	  *prev_envp = new_env;
	  continue;
	}
#endif

      for (int i = 0; i < sizeof (tunable_list) / sizeof (tunable_t); i++)
	{
	  tunable_t *cur = &tunable_list[i];

	  /* Skip over tunables that have either been set already or should be
	     skipped.  */
	  if (cur->initialized || cur->env_alias == NULL)
	    continue;

	  const char *name = cur->env_alias;

	  /* We have a match.  Initialize and move on to the next line.  */
	  if (tunable_is_name (name, envname))
	    {
	      /* For AT_SECURE binaries, we need to check the security settings of
		 the tunable and decide whether we read the value and also whether
		 we erase the value so that child processes don't inherit them in
		 the environment.  */
	      if (__libc_enable_secure)
		{
		  if (cur->security_level == TUNABLE_SECLEVEL_SXID_ERASE)
		    {
		      /* Erase the environment variable.  */
		      char **ep = prev_envp;

		      while (*ep != NULL)
			{
			  if (tunable_is_name (name, *ep))
			    {
			      char **dp = ep;

			      do
				dp[0] = dp[1];
			      while (*dp++);
			    }
			  else
			    ++ep;
			}
		      /* Reset the iterator so that we read the environment again
			 from the point we erased.  */
		      envp = prev_envp;
		    }

		  if (cur->security_level != TUNABLE_SECLEVEL_NONE)
		    continue;
		}

	      tunable_initialize (cur, envval);
	      break;
	    }
	}
    }
}

/* Set the tunable value.  This is called by the module that the tunable exists
   in. */
void
__tunable_get_val (tunable_id_t id, void *valp, tunable_callback_t callback)
{
  tunable_t *cur = &tunable_list[id];

  switch (cur->type.type_code)
    {
    case TUNABLE_TYPE_UINT_64:
	{
	  *((uint64_t *) valp) = (uint64_t) cur->val.numval;
	  break;
	}
    case TUNABLE_TYPE_INT_32:
	{
	  *((int32_t *) valp) = (int32_t) cur->val.numval;
	  break;
	}
    case TUNABLE_TYPE_SIZE_T:
	{
	  *((size_t *) valp) = (size_t) cur->val.numval;
	  break;
	}
    case TUNABLE_TYPE_STRING:
	{
	  *((const char **)valp) = cur->val.strval;
	  break;
	}
    default:
      __builtin_unreachable ();
    }

  if (cur->initialized && callback != NULL)
    callback (&cur->val);
}

rtld_hidden_def (__tunable_get_val)