From 429029a73ec2dba7f808f69ec8b9e3d84e13e804 Mon Sep 17 00:00:00 2001 From: DJ Delorie Date: Fri, 15 Jan 2021 19:50:00 -0500 Subject: [PATCH] nsswitch: do not reload if "/" changes https://sourceware.org/bugzilla/show_bug.cgi?id=27077 Before reloading nsswitch.conf, verify that the root directory hasn't changed - if it has, it's likely that we've entered a container and should not trust the nsswitch inside the container nor load any shared objects therein. Reviewed-by: Carlos O'Donell --- nss/Makefile | 2 +- nss/nss_database.c | 27 ++++++ nss/nss_module.c | 13 +++ nss/nss_module.h | 3 + nss/tst-reload2.c | 126 ++++++++++++++++++++++++++ nss/tst-reload2.root/etc/nsswitch.conf | 2 + nss/tst-reload2.root/subdir/etc/group | 1 + nss/tst-reload2.root/subdir/etc/nsswitch.conf | 2 + nss/tst-reload2.root/tst-reload2.script | 3 + 9 files changed, 178 insertions(+), 1 deletion(-) create mode 100644 nss/tst-reload2.c create mode 100644 nss/tst-reload2.root/etc/nsswitch.conf create mode 100644 nss/tst-reload2.root/subdir/etc/group create mode 100644 nss/tst-reload2.root/subdir/etc/nsswitch.conf create mode 100644 nss/tst-reload2.root/tst-reload2.script diff --git a/nss/Makefile b/nss/Makefile index 5f6bf59..0906202 100644 --- a/nss/Makefile +++ b/nss/Makefile @@ -67,7 +67,7 @@ tests-container = \ tst-nss-files-hosts-long \ tst-nss-db-endpwent \ tst-nss-db-endgrent \ - tst-reload1 + tst-reload1 tst-reload2 # Tests which need libdl ifeq (yes,$(build-shared)) diff --git a/nss/nss_database.c b/nss/nss_database.c index e719ec0..cf0306a 100644 --- a/nss/nss_database.c +++ b/nss/nss_database.c @@ -33,6 +33,11 @@ struct nss_database_state { struct nss_database_data data; __libc_lock_define (, lock); + /* If "/" changes, we switched into a container and do NOT want to + reload anything. This data must be persistent across + reloads. */ + ino64_t root_ino; + dev_t root_dev; }; @@ -54,6 +59,8 @@ global_state_allocate (void *closure) result->data.initialized = true; result->data.reload_disabled = false; __libc_lock_init (result->lock); + result->root_ino = 0; + result->root_dev = 0; } return result; } @@ -356,6 +363,8 @@ nss_database_check_reload_and_get (struct nss_database_state *local, nss_action_list *result, enum nss_database database_index) { + struct stat64 str; + /* Acquire MO is needed because the thread that sets reload_disabled may have loaded the configuration first, so synchronize with the Release MO store there. */ @@ -379,6 +388,24 @@ nss_database_check_reload_and_get (struct nss_database_state *local, __libc_lock_unlock (local->lock); return true; } + + /* Before we reload, verify that "/" hasn't changed. We assume that + errors here are very unlikely, but the chance that we're entering + a container is also very unlikely, so we err on the side of both + very unlikely things not happening at the same time. */ + if (__stat64 ("/", &str) != 0 + || (local->root_ino != 0 + && (str.st_ino != local->root_ino + || str.st_dev != local->root_dev))) + { + /* Change detected; disable reloading. */ + atomic_store_release (&local->data.reload_disabled, 1); + __libc_lock_unlock (local->lock); + __nss_module_disable_loading (); + return true; + } + local->root_ino = str.st_ino; + local->root_dev = str.st_dev; __libc_lock_unlock (local->lock); /* Avoid overwriting the global configuration until we have loaded diff --git a/nss/nss_module.c b/nss/nss_module.c index 1a93599..6c5f341 100644 --- a/nss/nss_module.c +++ b/nss/nss_module.c @@ -349,6 +349,19 @@ __nss_disable_nscd (void (*cb) (size_t, struct traced_file *)) } #endif +/* Block attempts to dlopen any module we haven't already opened. */ +void +__nss_module_disable_loading (void) +{ + __libc_lock_lock (nss_module_list_lock); + + for (struct nss_module *p = nss_module_list; p != NULL; p = p->next) + if (p->state == nss_module_uninitialized) + p->state = nss_module_failed; + + __libc_lock_unlock (nss_module_list_lock); +} + void __libc_freeres_fn_section __nss_module_freeres (void) { diff --git a/nss/nss_module.h b/nss/nss_module.h index 06e8c29..05c4791 100644 --- a/nss/nss_module.h +++ b/nss/nss_module.h @@ -87,6 +87,9 @@ bool __nss_module_load (struct nss_module *module) attribute_hidden; void *__nss_module_get_function (struct nss_module *module, const char *name) attribute_hidden; +/* Block attempts to dlopen any module we haven't already opened. */ +void __nss_module_disable_loading (void); + /* Called from __libc_freeres. */ void __nss_module_freeres (void) attribute_hidden; diff --git a/nss/tst-reload2.c b/nss/tst-reload2.c new file mode 100644 index 0000000..128db25 --- /dev/null +++ b/nss/tst-reload2.c @@ -0,0 +1,126 @@ +/* Test that reloading is disabled after a chroot. + Copyright (C) 2020-2021 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 + . */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include +#include +#include + +#include "nss_test.h" + +static struct passwd pwd_table1[] = + { + PWD_N (1234, "test1"), + PWD_N (4321, "test2"), + PWD_LAST () + }; + +static const char *group_4[] = { + "alpha", "beta", "gamma", "fred", NULL +}; + +static struct group group_table_data[] = + { + GRP (4), + GRP_LAST () + }; + +void +_nss_test1_init_hook (test_tables *t) +{ + t->pwd_table = pwd_table1; + t->grp_table = group_table_data; +} + +static struct passwd pwd_table2[] = + { + PWD_N (5, "test1"), + PWD_N (2468, "test2"), + PWD_LAST () + }; + +void +_nss_test2_init_hook (test_tables *t) +{ + t->pwd_table = pwd_table2; +} + +static int +do_test (void) +{ + struct passwd *pw; + struct group *gr; + char buf1[PATH_MAX]; + char buf2[PATH_MAX]; + + sprintf (buf1, "/subdir%s", support_slibdir_prefix); + xmkdirp (buf1, 0777); + + /* Copy this DSO into the chroot so it *could* be loaded. */ + sprintf (buf1, "%s/libnss_files.so.2", support_slibdir_prefix); + sprintf (buf2, "/subdir%s/libnss_files.so.2", support_slibdir_prefix); + support_copy_file (buf1, buf2); + + /* Check we're using the "outer" nsswitch.conf. */ + + /* This uses the test1 DSO. */ + pw = getpwnam ("test1"); + TEST_VERIFY (pw != NULL); + if (pw) + TEST_COMPARE (pw->pw_uid, 1234); + + /* This just loads the test2 DSO. */ + gr = getgrnam ("name4"); + + /* Change the root dir. */ + + TEST_VERIFY (chroot ("/subdir") == 0); + chdir ("/"); + + /* Check we're NOT using the "inner" nsswitch.conf. */ + + /* Both DSOs are loaded, which is used? */ + pw = getpwnam ("test2"); + TEST_VERIFY (pw != NULL); + if (pw) + TEST_VERIFY (pw->pw_uid != 2468); + + /* The "files" DSO should not be loaded. */ + gr = getgrnam ("test3"); + TEST_VERIFY (gr == NULL); + + /* We should still be using the old configuration. */ + pw = getpwnam ("test1"); + TEST_VERIFY (pw != NULL); + if (pw) + TEST_COMPARE (pw->pw_uid, 1234); + + return 0; +} + +#include diff --git a/nss/tst-reload2.root/etc/nsswitch.conf b/nss/tst-reload2.root/etc/nsswitch.conf new file mode 100644 index 0000000..570795a --- /dev/null +++ b/nss/tst-reload2.root/etc/nsswitch.conf @@ -0,0 +1,2 @@ +passwd: test1 +group: test2 diff --git a/nss/tst-reload2.root/subdir/etc/group b/nss/tst-reload2.root/subdir/etc/group new file mode 100644 index 0000000..e48646b --- /dev/null +++ b/nss/tst-reload2.root/subdir/etc/group @@ -0,0 +1 @@ +test3:x:123: diff --git a/nss/tst-reload2.root/subdir/etc/nsswitch.conf b/nss/tst-reload2.root/subdir/etc/nsswitch.conf new file mode 100644 index 0000000..f1d73f8 --- /dev/null +++ b/nss/tst-reload2.root/subdir/etc/nsswitch.conf @@ -0,0 +1,2 @@ +passwd: test2 +group: files diff --git a/nss/tst-reload2.root/tst-reload2.script b/nss/tst-reload2.root/tst-reload2.script new file mode 100644 index 0000000..c6ee4b8 --- /dev/null +++ b/nss/tst-reload2.root/tst-reload2.script @@ -0,0 +1,3 @@ +su +cp $B/nss/libnss_test1.so $L/libnss_test1.so.2 +cp $B/nss/libnss_test2.so $L/libnss_test2.so.2 -- 2.7.4