[PATCHv7] nss_db: protect against empty mappings

[DJ Delorie <dj@redhat.com>]

Andreas Schwab <schwab@suse.de> writes:
> That comment does not quite say that.  It should say that it's a symbol
> reference to the library (not a functional dependency).

I added a big comment to both of those explaining what the files were
for.

nss_db allows for getpwent et al to be called without a set*ent,
but it only works once.  After the last get*ent a set*ent is
required to restart, because the end*ent did not properly reset
the module.  Resetting it to NULL allows for a proper restart.

If the database doesn't exist, however, end*ent erroniously called
munmap which set errno.

The test case runs "makedb" inside the testroot, so needs selinux
DSOs installed.

2019-06-25  DJ Delorie  <dj@redhat.com>
	    Sergei Trofimovich <slyfox@inbox.ru>

	[BZ #24696]
	[BZ #24695]
	* nss/nss_db/db-open.c (internal_endent): Protect against NULL
	mappings.
	* nss/tst-nss-db-endgrent.c: New.
	* nss/tst-nss-db-endgrent.root: New.
	* nss/tst-nss-db-endpwent.c: New.
	* nss/tst-nss-db-endpwent.root: New.
	* nss/Makefile: Add new tests.
	* support/links-dso-program-c.c: Add selinux dependency.
	* support/links-dso-program.cc: Add selinux dependency.
	* support/Makefile: Build those with -lselinux if enabled.

diff --git a/nss/Makefile b/nss/Makefile
index 95081bddc5..a15c3b7d90 100644
--- a/nss/Makefile
+++ b/nss/Makefile
@@ -61,7 +61,9 @@ xtests			= bug-erange
 
 tests-container = \
 			  tst-nss-test3 \
-			  tst-nss-files-hosts-long
+			  tst-nss-files-hosts-long \
+			  tst-nss-db-endpwent \
+			  tst-nss-db-endgrent
 
 # Tests which need libdl
 ifeq (yes,$(build-shared))
diff --git a/nss/nss_db/db-open.c b/nss/nss_db/db-open.c
index 8a83d6b930..3fa11e9ab0 100644
--- a/nss/nss_db/db-open.c
+++ b/nss/nss_db/db-open.c
@@ -63,5 +63,9 @@ internal_setent (const char *file, struct nss_db_map *mapping)
 void
 internal_endent (struct nss_db_map *mapping)
 {
-  munmap (mapping->header, mapping->len);
+  if (mapping->header != NULL)
+    {
+      munmap (mapping->header, mapping->len);
+      mapping->header = NULL;
+    }
 }
diff --git a/nss/tst-nss-db-endgrent.c b/nss/tst-nss-db-endgrent.c
new file mode 100644
index 0000000000..367cc6c901
--- /dev/null
+++ b/nss/tst-nss-db-endgrent.c
@@ -0,0 +1,54 @@
+/* Test for endgrent changing errno for BZ #24696
+   Copyright (C) 2019 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 <stdlib.h>
+#include <sys/types.h>
+#include <grp.h>
+#include <unistd.h>
+#include <errno.h>
+
+#include <support/check.h>
+#include <support/support.h>
+
+/* The following test verifies that if the db NSS Service is initialized
+   with no database (getgrent), that a subsequent closure (endgrent) does
+   not set errno. In the case of the db service it is not an error to close
+   the service and so it should not set errno.  */
+
+static int
+do_test (void)
+{
+  /* Just make sure it's not there, although usually it won't be.  */
+  unlink ("/var/db/group.db");
+
+  /* This, in conjunction with the testroot's nsswitch.conf, causes
+     the nss_db module to be "connected" and initialized - but the
+     testroot has no group.db, so no mapping will be created.  */
+  getgrent ();
+
+  errno = 0;
+
+  /* Before the fix, this would call munmap (NULL) and set errno.  */
+  endgrent ();
+
+  if (errno != 0)
+    FAIL_EXIT1 ("endgrent set errno to %d\n", errno);
+
+  return 0;
+}
+#include <support/test-driver.c>
diff --git a/nss/tst-nss-db-endgrent.root/etc/nsswitch.conf b/nss/tst-nss-db-endgrent.root/etc/nsswitch.conf
new file mode 100644
index 0000000000..21471df94f
--- /dev/null
+++ b/nss/tst-nss-db-endgrent.root/etc/nsswitch.conf
@@ -0,0 +1 @@
+group : db files
diff --git a/nss/tst-nss-db-endpwent.c b/nss/tst-nss-db-endpwent.c
new file mode 100644
index 0000000000..0a8b3184b0
--- /dev/null
+++ b/nss/tst-nss-db-endpwent.c
@@ -0,0 +1,70 @@
+/* Test for endpwent->getpwent crash for BZ #24695
+   Copyright (C) 2019 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 <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <pwd.h>
+
+#include <support/support.h>
+#include <support/check.h>
+
+/* It is entirely allowed to start with a getpwent call without
+   resetting the state of the service via a call to setpwent.
+   You can also call getpwent more times than you have entries in
+   the service, and it should not fail.  This test iteratates the
+   database once, gets to the end, and then attempts a second
+   iteration to look for crashes.  */
+
+static void
+try_it (void)
+{
+  struct passwd *pw;
+
+  /* setpwent is intentionally omitted here.  The first call to
+     getpwent detects that it's first and initializes.  The second
+     time try_it is called, this "first call" was not detected before
+     the fix, and getpwent would crash.  */
+
+  while ((pw = getpwent ()) != NULL)
+    ;
+
+  /* We only care if this segfaults or not.  */
+  endpwent ();
+}
+
+static int
+do_test (void)
+{
+  char *cmd;
+  const char *rest;
+
+  rest = "/makedb -o /var/db/passwd.db /var/db/passwd.in";
+  cmd = (char *) xmalloc (strlen (support_bindir_prefix)
+				+ strlen (rest) + 1);
+  strcpy (cmd, support_bindir_prefix);
+  strcat (cmd, rest);
+
+  system (cmd);
+
+  try_it ();
+  try_it ();
+
+  return 0;
+}
+#include <support/test-driver.c>
diff --git a/nss/tst-nss-db-endpwent.root/etc/nsswitch.conf b/nss/tst-nss-db-endpwent.root/etc/nsswitch.conf
new file mode 100644
index 0000000000..593ffc564a
--- /dev/null
+++ b/nss/tst-nss-db-endpwent.root/etc/nsswitch.conf
@@ -0,0 +1 @@
+passwd: db
diff --git a/nss/tst-nss-db-endpwent.root/var/db/passwd.in b/nss/tst-nss-db-endpwent.root/var/db/passwd.in
new file mode 100644
index 0000000000..98f39126ef
--- /dev/null
+++ b/nss/tst-nss-db-endpwent.root/var/db/passwd.in
@@ -0,0 +1,4 @@
+.root root:x:0:0:root:/root:/bin/bash
+=0 root:x:0:0:root:/root:/bin/bash
+.bin bin:x:1:1:bin:/bin:/sbin/nologin
+=1 bin:x:1:1:bin:/bin:/sbin/nologin
diff --git a/support/Makefile b/support/Makefile
index 56c1ed43bb..ab66913a02 100644
--- a/support/Makefile
+++ b/support/Makefile
@@ -191,6 +191,11 @@ LINKS_DSO_PROGRAM = links-dso-program
 LDLIBS-links-dso-program = -lstdc++ -lgcc -lgcc_s $(libunwind)
 endif
 
+ifeq (yes,$(have-selinux))
+LDLIBS-$(LINKS_DSO_PROGRAM) += -lselinux
+endif
+
+
 LDLIBS-test-container = $(libsupport)
 
 others += test-container
diff --git a/support/links-dso-program-c.c b/support/links-dso-program-c.c
index d28a28a0d0..5fcbab2c17 100644
--- a/support/links-dso-program-c.c
+++ b/support/links-dso-program-c.c
@@ -1,9 +1,26 @@
 #include <stdio.h>
 
+/* makedb needs selinux dso's.  */
+#ifdef HAVE_SELINUX
+# include <selinux/selinux.h>
+#endif
+
+/* The purpose of this file is to indicate to the build system which
+   shared objects need to be copied into the testroot, such as gcc or
+   selinux support libraries.  This program is never executed, only
+   scanned for dependencies on shared objects, so the code below may
+   seem weird - it's written to survive gcc optimization and force
+   such dependencies.
+*/
+
 int
 main (int argc, char **argv)
 {
   /* Complexity to keep gcc from optimizing this away.  */
   printf ("This is a test %s.\n", argc > 1 ? argv[1] : "null");
+#ifdef HAVE_SELINUX
+  /* This exists to force libselinux.so to be required.  */
+  printf ("selinux %d\n", is_selinux_enabled ());
+#endif
   return 0;
 }
diff --git a/support/links-dso-program.cc b/support/links-dso-program.cc
index dba6976c06..4bc2411086 100644
--- a/support/links-dso-program.cc
+++ b/support/links-dso-program.cc
@@ -1,11 +1,28 @@
 #include <iostream>
 
+/* makedb needs selinux dso's.  */
+#ifdef HAVE_SELINUX
+# include <selinux/selinux.h>
+#endif
+
 using namespace std;
 
+/* The purpose of this file is to indicate to the build system which
+   shared objects need to be copied into the testroot, such as gcc or
+   selinux support libraries.  This program is never executed, only
+   scanned for dependencies on shared objects, so the code below may
+   seem weird - it's written to survive gcc optimization and force
+   such dependencies.
+*/
+
 int
 main (int argc, char **argv)
 {
   /* Complexity to keep gcc from optimizing this away.  */
   cout << (argc > 1 ? argv[1] : "null");
+#ifdef HAVE_SELINUX
+  /* This exists to force libselinux.so to be required.  */
+  cout << "selinux " << is_selinux_enabled ();
+#endif
   return 0;
 }