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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 <carlos@redhat.com>
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@ -402,7 +402,6 @@ nss_database_check_reload_and_get (struct nss_database_state *local,
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atomic_store_release (&local->data.reload_disabled, 1);
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atomic_store_release (&local->data.reload_disabled, 1);
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*result = local->data.services[database_index];
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*result = local->data.services[database_index];
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__libc_lock_unlock (local->lock);
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__libc_lock_unlock (local->lock);
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__nss_module_disable_loading ();
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return true;
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return true;
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}
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}
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local->root_ino = str.st_ino;
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local->root_ino = str.st_ino;
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@ -26,6 +26,7 @@
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#include <pwd.h>
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#include <pwd.h>
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#include <grp.h>
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#include <grp.h>
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#include <unistd.h>
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#include <unistd.h>
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#include <netdb.h>
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#include <support/support.h>
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#include <support/support.h>
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#include <support/check.h>
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#include <support/check.h>
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@ -48,7 +49,7 @@ static const char *group_4[] = {
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"alpha", "beta", "gamma", "fred", NULL
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"alpha", "beta", "gamma", "fred", NULL
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};
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};
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static struct group group_table_data[] =
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static struct group group_table_data1[] =
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{
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{
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GRP (4),
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GRP (4),
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GRP_LAST ()
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GRP_LAST ()
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@ -58,7 +59,7 @@ void
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_nss_test1_init_hook (test_tables *t)
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_nss_test1_init_hook (test_tables *t)
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{
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{
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t->pwd_table = pwd_table1;
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t->pwd_table = pwd_table1;
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t->grp_table = group_table_data;
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t->grp_table = group_table_data1;
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}
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}
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static struct passwd pwd_table2[] =
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static struct passwd pwd_table2[] =
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@ -68,10 +69,21 @@ static struct passwd pwd_table2[] =
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PWD_LAST ()
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PWD_LAST ()
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};
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};
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static const char *group_5[] = {
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"fred", NULL
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};
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static struct group group_table_data2[] =
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{
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GRP (5),
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GRP_LAST ()
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};
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void
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void
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_nss_test2_init_hook (test_tables *t)
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_nss_test2_init_hook (test_tables *t)
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{
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{
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t->pwd_table = pwd_table2;
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t->pwd_table = pwd_table2;
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t->grp_table = group_table_data2;
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}
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}
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static int
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static int
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@ -79,6 +91,7 @@ do_test (void)
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{
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{
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struct passwd *pw;
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struct passwd *pw;
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struct group *gr;
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struct group *gr;
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struct hostent *he;
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char buf1[PATH_MAX];
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char buf1[PATH_MAX];
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char buf2[PATH_MAX];
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char buf2[PATH_MAX];
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@ -99,7 +112,9 @@ do_test (void)
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TEST_COMPARE (pw->pw_uid, 1234);
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TEST_COMPARE (pw->pw_uid, 1234);
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/* This just loads the test2 DSO. */
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/* This just loads the test2 DSO. */
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gr = getgrnam ("name4");
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gr = getgrgid (5);
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TEST_VERIFY (gr != NULL);
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/* Change the root dir. */
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/* Change the root dir. */
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@ -114,15 +129,21 @@ do_test (void)
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if (pw)
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if (pw)
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TEST_VERIFY (pw->pw_uid != 2468);
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TEST_VERIFY (pw->pw_uid != 2468);
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/* The "files" DSO should not be loaded. */
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gr = getgrnam ("test3");
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TEST_VERIFY (gr == NULL);
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/* We should still be using the old configuration. */
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/* We should still be using the old configuration. */
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pw = getpwnam ("test1");
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pw = getpwnam ("test1");
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TEST_VERIFY (pw != NULL);
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TEST_VERIFY (pw != NULL);
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if (pw)
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if (pw)
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TEST_COMPARE (pw->pw_uid, 1234);
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TEST_COMPARE (pw->pw_uid, 1234);
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gr = getgrgid (5);
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TEST_VERIFY (gr != NULL);
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gr = getgrnam ("name4");
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TEST_VERIFY (gr == NULL);
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/* hosts in the outer nsswitch is files; the inner one is test1.
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Verify that we're still using the outer nsswitch *and* that we
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can load the files DSO. */
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he = gethostbyname ("test2");
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TEST_VERIFY (he != NULL);
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return 0;
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return 0;
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}
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}
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1
nss/tst-reload2.root/etc/hosts
Normal file
1
nss/tst-reload2.root/etc/hosts
Normal file
@ -0,0 +1 @@
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1.2.3.4 test1
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@ -1,2 +1,3 @@
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passwd: test1
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passwd: test1
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group: test2
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group: test2
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hosts: files
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1
nss/tst-reload2.root/subdir/etc/hosts
Normal file
1
nss/tst-reload2.root/subdir/etc/hosts
Normal file
@ -0,0 +1 @@
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1.2.3.4 test2
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@ -1,2 +1,3 @@
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passwd: test2
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passwd: test2
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group: files
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group: files
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hosts: test1
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