/* 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)