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-rw-r--r--elf/dl-tunables.c320
1 files changed, 320 insertions, 0 deletions
diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
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+/* The tunable framework. See the README.tunables to know how to use the
+ tunable in a glibc module.
+
+ Copyright (C) 2016 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
+ <http://www.gnu.org/licenses/>. */
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <libc-internal.h>
+#include <sysdep.h>
+#include <fcntl.h>
+#include <ldsodefs.h>
+
+#define TUNABLES_INTERNAL 1
+#include "dl-tunables.h"
+
+/* Compare environment names, bounded by the name hardcoded in glibc. */
+static bool
+is_name (const char *orig, const char *envname)
+{
+ for (;*orig != '\0' && *envname != '\0'; envname++, orig++)
+ if (*orig != *envname)
+ break;
+
+ /* The ENVNAME is immediately followed by a value. */
+ if (*orig == '\0' && *envname == '=')
+ return true;
+ else
+ return false;
+}
+
+static char **
+get_next_env (char **envp, char **name, size_t *namelen, char **val)
+{
+ while (envp != NULL && *envp != NULL)
+ {
+ 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];
+
+ return ++envp;
+ }
+
+ return NULL;
+}
+
+static int
+tunables_unsetenv (char **ep, const char *name)
+{
+ while (*ep != NULL)
+ {
+ size_t cnt = 0;
+
+ while ((*ep)[cnt] == name[cnt] && name[cnt] != '\0')
+ ++cnt;
+
+ if (name[cnt] == '\0' && (*ep)[cnt] == '=')
+ {
+ /* Found it. Remove this pointer by moving later ones to
+ the front. */
+ char **dp = ep;
+
+ do
+ dp[0] = dp[1];
+ while (*dp++);
+ /* Continue the loop in case NAME appears again. */
+ }
+ else
+ ++ep;
+ }
+
+ return 0;
+}
+
+/* A stripped down strtoul-like implementation for very early use. It does not
+ set errno if the result is outside bounds because it gets called before
+ errno may have been set up. */
+static unsigned long int
+tunables_strtoul (const char *nptr)
+{
+ unsigned long int result = 0;
+ long int sign = 1;
+ unsigned max_digit;
+
+ while (*nptr == ' ' || *nptr == '\t')
+ ++nptr;
+
+ if (*nptr == '-')
+ {
+ sign = -1;
+ ++nptr;
+ }
+ else if (*nptr == '+')
+ ++nptr;
+
+ if (*nptr < '0' || *nptr > '9')
+ return 0UL;
+
+ int base = 10;
+ max_digit = 9;
+ if (*nptr == '0')
+ {
+ if (nptr[1] == 'x' || nptr[1] == 'X')
+ {
+ base = 16;
+ nptr += 2;
+ }
+ else
+ {
+ base = 8;
+ max_digit = 7;
+ }
+ }
+
+ while (1)
+ {
+ unsigned long int digval;
+ if (*nptr >= '0' && *nptr <= '0' + max_digit)
+ digval = *nptr - '0';
+ else if (base == 16)
+ {
+ if (*nptr >= 'a' && *nptr <= 'f')
+ digval = *nptr - 'a' + 10;
+ else if (*nptr >= 'A' && *nptr <= 'F')
+ digval = *nptr - 'A' + 10;
+ else
+ break;
+ }
+ else
+ break;
+
+ if (result > ULONG_MAX / base
+ || (result == ULONG_MAX / base && digval > ULONG_MAX % base))
+ return ULONG_MAX;
+ result *= base;
+ result += digval;
+ ++nptr;
+ }
+
+ return result * sign;
+}
+
+/* Initialize the internal type if the value validates either using the
+ explicit constraints of the tunable or with the implicit constraints of its
+ type. */
+static void
+tunable_set_val_if_valid_range (tunable_t *cur, const char *strval,
+ int64_t default_min, int64_t default_max)
+{
+ int64_t val = tunables_strtoul (strval);
+
+ int64_t min = cur->type.min;
+ int64_t max = cur->type.max;
+
+ if (min == max)
+ {
+ min = default_min;
+ max = default_max;
+ }
+
+ if (val >= min && val <= max)
+ {
+ cur->val.numval = val;
+ cur->strval = strval;
+ }
+}
+
+/* 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)
+{
+ switch (cur->type.type_code)
+ {
+ case TUNABLE_TYPE_INT_32:
+ {
+ tunable_set_val_if_valid_range (cur, strval, INT32_MIN, INT32_MAX);
+ break;
+ }
+ case TUNABLE_TYPE_SIZE_T:
+ {
+ tunable_set_val_if_valid_range (cur, strval, 0, SIZE_MAX);
+ break;
+ }
+ case TUNABLE_TYPE_STRING:
+ {
+ cur->val.strval = cur->strval = strval;
+ break;
+ }
+ default:
+ __builtin_unreachable ();
+ }
+}
+
+/* Disable a tunable if it is set. */
+static void
+disable_tunable (tunable_id_t id, char **envp)
+{
+ const char *env_alias = tunable_list[id].env_alias;
+
+ if (env_alias != NULL)
+ tunables_unsetenv (envp, tunable_list[id].env_alias);
+}
+
+/* Disable the glibc.malloc.check tunable in SETUID/SETGID programs unless
+ the system administrator overrides it by creating 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 inline void
+__always_inline
+maybe_disable_malloc_check (void)
+{
+ if (__libc_enable_secure && __access_noerrno ("/etc/suid-debug", F_OK) != 0)
+ disable_tunable (TUNABLE_ENUM_NAME(glibc, malloc, check), __environ);
+}
+
+/* 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;
+
+ maybe_disable_malloc_check ();
+
+ while ((envp = get_next_env (envp, &envname, &len, &envval)) != NULL)
+ {
+ 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->strval != NULL || cur->env_alias == NULL
+ || (__libc_enable_secure && !cur->is_secure))
+ continue;
+
+ const char *name = cur->env_alias;
+
+ /* We have a match. Initialize and move on to the next line. */
+ if (is_name (name, envname))
+ {
+ tunable_initialize (cur, envval);
+ break;
+ }
+ }
+ }
+}
+
+/* Set the tunable value. This is called by the module that the tunable exists
+ in. */
+void
+__tunable_set_val (tunable_id_t id, void *valp, tunable_callback_t callback)
+{
+ tunable_t *cur = &tunable_list[id];
+
+ /* Don't do anything if our tunable was not set during initialization or if
+ it failed validation. */
+ if (cur->strval == NULL)
+ return;
+
+ if (valp == NULL)
+ goto cb;
+
+ switch (cur->type.type_code)
+ {
+ 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 ();
+ }
+
+cb:
+ if (callback)
+ callback (&cur->val);
+}
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