From 58673149f37389495c098421085ffdb468b3f7ad Mon Sep 17 00:00:00 2001 From: DJ Delorie Date: Thu, 18 Feb 2021 15:26:30 -0500 Subject: nss: Re-enable NSS module loading after chroot [BZ #27389] The glibc 2.33 release enabled /etc/nsswitch.conf reloading, and to prevent potential security issues like CVE-2019-14271 the re-loading of nsswitch.conf and all mdoules was disabled when the root filesystem changes (see bug 27077). Unfortunately php-lpfm and openldap both require the ability to continue to load NSS modules after chroot. The packages do not exec after the chroot, and so do not cause the protections to be reset. The only solution is to re-enable only NSS module loading (not nsswitch.conf reloading) and so get back the previous glibc behaviour. In the future we may introduce a way to harden applications so they do not reload NSS modules once the root filesystem changes, or that only files/dns are available pre-loaded (or builtin). Reviewed-by: Carlos O'Donell --- nss/nss_database.c | 1 - nss/tst-reload2.c | 35 +++++++++++++++++++++------ nss/tst-reload2.root/etc/hosts | 1 + nss/tst-reload2.root/etc/nsswitch.conf | 1 + nss/tst-reload2.root/subdir/etc/hosts | 1 + nss/tst-reload2.root/subdir/etc/nsswitch.conf | 1 + 6 files changed, 32 insertions(+), 8 deletions(-) create mode 100644 nss/tst-reload2.root/etc/hosts create mode 100644 nss/tst-reload2.root/subdir/etc/hosts (limited to 'nss') diff --git a/nss/nss_database.c b/nss/nss_database.c index e1bef6bd75..fb72d0cc03 100644 --- a/nss/nss_database.c +++ b/nss/nss_database.c @@ -402,7 +402,6 @@ nss_database_check_reload_and_get (struct nss_database_state *local, atomic_store_release (&local->data.reload_disabled, 1); *result = local->data.services[database_index]; __libc_lock_unlock (local->lock); - __nss_module_disable_loading (); return true; } local->root_ino = str.st_ino; diff --git a/nss/tst-reload2.c b/nss/tst-reload2.c index 5dae16b4f0..5ecb032e9f 100644 --- a/nss/tst-reload2.c +++ b/nss/tst-reload2.c @@ -26,6 +26,7 @@ #include #include #include +#include #include #include @@ -48,7 +49,7 @@ static const char *group_4[] = { "alpha", "beta", "gamma", "fred", NULL }; -static struct group group_table_data[] = +static struct group group_table_data1[] = { GRP (4), GRP_LAST () @@ -58,7 +59,7 @@ void _nss_test1_init_hook (test_tables *t) { t->pwd_table = pwd_table1; - t->grp_table = group_table_data; + t->grp_table = group_table_data1; } static struct passwd pwd_table2[] = @@ -68,10 +69,21 @@ static struct passwd pwd_table2[] = PWD_LAST () }; +static const char *group_5[] = { + "fred", NULL +}; + +static struct group group_table_data2[] = + { + GRP (5), + GRP_LAST () + }; + void _nss_test2_init_hook (test_tables *t) { t->pwd_table = pwd_table2; + t->grp_table = group_table_data2; } static int @@ -79,6 +91,7 @@ do_test (void) { struct passwd *pw; struct group *gr; + struct hostent *he; char buf1[PATH_MAX]; char buf2[PATH_MAX]; @@ -99,7 +112,9 @@ do_test (void) TEST_COMPARE (pw->pw_uid, 1234); /* This just loads the test2 DSO. */ - gr = getgrnam ("name4"); + gr = getgrgid (5); + TEST_VERIFY (gr != NULL); + /* Change the root dir. */ @@ -114,15 +129,21 @@ do_test (void) 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); + gr = getgrgid (5); + TEST_VERIFY (gr != NULL); + gr = getgrnam ("name4"); + TEST_VERIFY (gr == NULL); + + /* hosts in the outer nsswitch is files; the inner one is test1. + Verify that we're still using the outer nsswitch *and* that we + can load the files DSO. */ + he = gethostbyname ("test2"); + TEST_VERIFY (he != NULL); return 0; } diff --git a/nss/tst-reload2.root/etc/hosts b/nss/tst-reload2.root/etc/hosts new file mode 100644 index 0000000000..bbd9e494ef --- /dev/null +++ b/nss/tst-reload2.root/etc/hosts @@ -0,0 +1 @@ +1.2.3.4 test1 diff --git a/nss/tst-reload2.root/etc/nsswitch.conf b/nss/tst-reload2.root/etc/nsswitch.conf index 570795ae22..688a589519 100644 --- a/nss/tst-reload2.root/etc/nsswitch.conf +++ b/nss/tst-reload2.root/etc/nsswitch.conf @@ -1,2 +1,3 @@ passwd: test1 group: test2 +hosts: files diff --git a/nss/tst-reload2.root/subdir/etc/hosts b/nss/tst-reload2.root/subdir/etc/hosts new file mode 100644 index 0000000000..0a2cbd4337 --- /dev/null +++ b/nss/tst-reload2.root/subdir/etc/hosts @@ -0,0 +1 @@ +1.2.3.4 test2 diff --git a/nss/tst-reload2.root/subdir/etc/nsswitch.conf b/nss/tst-reload2.root/subdir/etc/nsswitch.conf index f1d73f8765..fea271869e 100644 --- a/nss/tst-reload2.root/subdir/etc/nsswitch.conf +++ b/nss/tst-reload2.root/subdir/etc/nsswitch.conf @@ -1,2 +1,3 @@ passwd: test2 group: files +hosts: test1 -- cgit v1.2.3