Harden putpwent, putgrent, putspent, putspent against injection [BZ #18724]

This prevents injection of ':' and '\n' into output functions which
use the NSS files database syntax.  Critical fields (user/group names
and file system paths) are checked strictly.  For backwards
compatibility, the GECOS field is rewritten instead.

The getent program is adjusted to use the put*ent functions in libc,
instead of local copies.  This changes the behavior of getent if user
names start with '-' or '+'.

22 files changed, 1018 insertions, 109 deletions

diff --git a/ChangeLog b/ChangeLog
index d410e0feef..20953eebc9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,41 @@
+2015-10-02  Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #18724]
+	* include/nss.h (NSS_INVALID_FIELD_CHARACTERS): Define.
+	(__nss_invalid_field_characters, __nss_valid_field)
+	(__nss_valid_list_field, __nss_rewrite_field): Declare.
+	* nss/valid_field.c, nss/valid_list_field, nss/rewrite_field.c,
+	tst-field.c: New file.
+	* nss/Makefile (routines): Add valid_field, rewrite_field.
+	(tests-static): Define unconditionally.
+	(tests): Include tests-static.
+	[build-static-nss] (tests-static): Use append.
+	[build-static-nss] (tests): Remove modification.
+	* nss/getent.c (print_group): Call putgrent.  Report error.
+	(print_gshadow): Call putsgent.  Report error.
+	(print_passwd): Call putpwent.  Report error.
+	(print_shadow): Call putspent.  Report error.
+	* include/pwd.h: Include <nss.h> instead of <nss/nss.h>.
+	* pwd/pwd.h (putpwent): Remove incorrect nonnull attribute.
+	* pwd/putpwent.c (putpwent): Use ISO function definition.  Check
+	name, password, directory, shell fields for valid syntax.  Rewrite
+	GECOS field to match syntax.
+	* pwd/Makefile (tests): Add tst-putpwent.
+	* pwd/tst-putpwent.c: New file.
+	* grp/putgrent.c (putgrent): Convert to ISO function definition.
+	Check grName, grpasswd, gr_mem fields for valid syntax.
+	Change loop variable i to size_t.
+	* grp/Makefile (tests): Add tst-putgrent.
+	* grp/tst-putgrent.c: New file.
+	* shadow/putspent.c (putspent): Check sp_namp, sp_pwdp fields for
+	valid syntax.
+	* shadow/Makefile (tests): Add tst-putspent.
+	* shadow/tst-putspent.c: New file.
+	* gshadow/putsgent.c (putsgent): Check sg_namp, sg_passwd, sg_adm,
+	sg_mem fields for valid syntax.
+	* gshadow/Makefile (tests): Add tst-putsgent.
+	* gshadow/tst-putsgent.c: New file.
+
 2015-10-01  Gabriel F. T. Gomes  <gftg@linux.vnet.ibm.com>
 
 	* sysdeps/powerpc/powerpc64/power8/strncpy.S: Added comments to some
diff --git a/NEWS b/NEWS
index e8b59a4676..4634b74ebf 100644
--- a/NEWS
+++ b/NEWS
@@ -13,11 +13,11 @@ Version 2.23
   15918, 16141, 16296, 16347, 16415, 16517, 16519, 16520, 16521, 16620,
   16734, 16973, 16985, 17118, 17243, 17244, 17250, 17441, 17787, 17886,
   17887, 17905, 18084, 18086, 18240, 18265, 18370, 18421, 18480, 18525,
-  18595, 18610, 18618, 18647, 18661, 18674, 18675, 18681, 18757, 18778,
-  18781, 18787, 18789, 18790, 18795, 18796, 18803, 18820, 18823, 18824,
-  18825, 18857, 18863, 18870, 18872, 18873, 18875, 18887, 18921, 18951,
-  18952, 18956, 18961, 18966, 18967, 18969, 18970, 18977, 18980, 18981,
-  18985, 19003, 19016, 19032, 19046.
+  18595, 18610, 18618, 18647, 18661, 18674, 18675, 18681, 18724, 18757,
+  18778, 18781, 18787, 18789, 18790, 18795, 18796, 18803, 18820, 18823,
+  18824, 18825, 18857, 18863, 18870, 18872, 18873, 18875, 18887, 18921,
+  18951, 18952, 18956, 18961, 18966, 18967, 18969, 18970, 18977, 18980,
+  18981, 18985, 19003, 19016, 19032, 19046.
 
 * The obsolete header <regexp.h> has been removed.  Programs that require
   this header must be updated to use <regex.h> instead.
diff --git a/grp/Makefile b/grp/Makefile
index c63b552a65..ed8cc2b056 100644
--- a/grp/Makefile
+++ b/grp/Makefile
@@ -28,7 +28,7 @@ routines := fgetgrent initgroups setgroups \
 	    getgrent getgrgid getgrnam putgrent \
 	    getgrent_r getgrgid_r getgrnam_r fgetgrent_r
 
-tests := testgrp
+tests := testgrp tst-putgrent
 
 ifeq (yes,$(build-shared))
 test-srcs :=  tst_fgetgrent
diff --git a/grp/putgrent.c b/grp/putgrent.c
index e4d662c6b5..1ac7f19a0b 100644
--- a/grp/putgrent.c
+++ b/grp/putgrent.c
@@ -16,7 +16,9 @@
    <http://www.gnu.org/licenses/>.  */
 
 #include <errno.h>
+#include <nss.h>
 #include <stdio.h>
+#include <string.h>
 #include <grp.h>
 
 #define flockfile(s) _IO_flockfile (s)
@@ -27,13 +29,14 @@
 /* Write an entry to the given stream.
    This must know the format of the group file.  */
 int
-putgrent (gr, stream)
-     const struct group *gr;
-     FILE *stream;
+putgrent (const struct group *gr, FILE *stream)
 {
   int retval;
 
-  if (__glibc_unlikely (gr == NULL) || __glibc_unlikely (stream == NULL))
+  if (__glibc_unlikely (gr == NULL) || __glibc_unlikely (stream == NULL)
+      || gr->gr_name == NULL || !__nss_valid_field (gr->gr_name)
+      || !__nss_valid_field (gr->gr_passwd)
+      || !__nss_valid_list_field (gr->gr_mem))
     {
       __set_errno (EINVAL);
       return -1;
@@ -56,9 +59,7 @@ putgrent (gr, stream)
 
   if (gr->gr_mem != NULL)
     {
-      int i;
-
-      for (i = 0 ; gr->gr_mem[i] != NULL; i++)
+      for (size_t i = 0; gr->gr_mem[i] != NULL; i++)
 	if (fprintf (stream, i == 0 ? "%s" : ",%s", gr->gr_mem[i]) < 0)
 	  {
 	    /* What else can we do?  */
diff --git a/grp/tst-putgrent.c b/grp/tst-putgrent.c
new file mode 100644
index 0000000000..0a07ef6ac1
--- /dev/null
+++ b/grp/tst-putgrent.c
@@ -0,0 +1,167 @@
+/* Test for processing of invalid group entries.  [BZ #18724]
+   Copyright (C) 2015 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 <errno.h>
+#include <grp.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static bool errors;
+
+static void
+check (struct group e, const char *expected)
+{
+  char *buf;
+  size_t buf_size;
+  FILE *f = open_memstream (&buf, &buf_size);
+
+  if (f == NULL)
+    {
+      printf ("open_memstream: %m\n");
+      errors = true;
+      return;
+    }
+
+  int ret = putgrent (&e, f);
+
+  if (expected == NULL)
+    {
+      if (ret == -1)
+	{
+	  if (errno != EINVAL)
+	    {
+	      printf ("putgrent: unexpected error code: %m\n");
+	      errors = true;
+	    }
+	}
+      else
+	{
+	  printf ("putgrent: unexpected success (\"%s\", \"%s\")\n",
+		  e.gr_name, e.gr_passwd);
+	  errors = true;
+	}
+    }
+  else
+    {
+      /* Expect success.  */
+      size_t expected_length = strlen (expected);
+      if (ret == 0)
+	{
+	  long written = ftell (f);
+
+	  if (written <= 0 || fflush (f) < 0)
+	    {
+	      printf ("stream error: %m\n");
+	      errors = true;
+	    }
+	  else if (buf[written - 1] != '\n')
+	    {
+	      printf ("FAILED: \"%s\" without newline\n", expected);
+	      errors = true;
+	    }
+	  else if (strncmp (buf, expected, written - 1) != 0
+		   || written - 1 != expected_length)
+	    {
+	      buf[written - 1] = '\0';
+	      printf ("FAILED: \"%s\" (%ld), expected \"%s\" (%zu)\n",
+		      buf, written - 1, expected, expected_length);
+	      errors = true;
+	    }
+	}
+      else
+	{
+	  printf ("FAILED: putgrent (expected \"%s\"): %m\n", expected);
+	  errors = true;
+	}
+    }
+
+  fclose (f);
+  free (buf);
+}
+
+static int
+do_test (void)
+{
+  check ((struct group) {
+      .gr_name = (char *) "root",
+    },
+    "root::0:");
+  check ((struct group) {
+      .gr_name = (char *) "root",
+      .gr_passwd = (char *) "password",
+      .gr_gid = 1234,
+      .gr_mem = (char *[2]) {(char *) "member1", NULL}
+    },
+    "root:password:1234:member1");
+  check ((struct group) {
+      .gr_name = (char *) "root",
+      .gr_passwd = (char *) "password",
+      .gr_gid = 1234,
+      .gr_mem = (char *[3]) {(char *) "member1", (char *) "member2", NULL}
+    },
+    "root:password:1234:member1,member2");
+
+  /* Bad values.  */
+  {
+    static const char *const bad_strings[] = {
+      ":",
+      "\n",
+      ":bad",
+      "\nbad",
+      "b:ad",
+      "b\nad",
+      "bad:",
+      "bad\n",
+      "b:a\nd"
+      ",",
+      "\n,",
+      ":,",
+      ",bad",
+      "b,ad",
+      "bad,",
+      NULL
+    };
+    for (const char *const *bad = bad_strings; *bad != NULL; ++bad)
+      {
+	char *members[]
+	  = {(char *) "first", (char *) *bad, (char *) "last", NULL};
+	if (strpbrk (*bad, ":\n") != NULL)
+	  {
+	    check ((struct group) {
+		.gr_name = (char *) *bad,
+	      }, NULL);
+	    check ((struct group) {
+		.gr_name = (char *) "root",
+		.gr_passwd = (char *) *bad,
+	      }, NULL);
+	  }
+	check ((struct group) {
+	    .gr_name = (char *) "root",
+	    .gr_passwd = (char *) "password",
+	    .gr_mem = members,
+	  }, NULL);
+      }
+  }
+
+  return errors;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/gshadow/Makefile b/gshadow/Makefile
index 883e1c8a2a..c811041a55 100644
--- a/gshadow/Makefile
+++ b/gshadow/Makefile
@@ -26,7 +26,7 @@ headers		= gshadow.h
 routines	= getsgent getsgnam sgetsgent fgetsgent putsgent \
 		  getsgent_r getsgnam_r sgetsgent_r fgetsgent_r
 
-tests = tst-gshadow
+tests = tst-gshadow tst-putsgent
 
 CFLAGS-getsgent_r.c = -fexceptions
 CFLAGS-getsgent.c = -fexceptions
diff --git a/gshadow/putsgent.c b/gshadow/putsgent.c
index 0b2cad6eaa..c1cb921595 100644
--- a/gshadow/putsgent.c
+++ b/gshadow/putsgent.c
@@ -15,9 +15,11 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
+#include <errno.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <gshadow.h>
+#include <nss.h>
 
 #define _S(x)	x ? x : ""
 
@@ -29,6 +31,15 @@ putsgent (const struct sgrp *g, FILE *stream)
 {
   int errors = 0;
 
+  if (g->sg_namp == NULL || !__nss_valid_field (g->sg_namp)
+      || !__nss_valid_field (g->sg_passwd)
+      || !__nss_valid_list_field (g->sg_adm)
+      || !__nss_valid_list_field (g->sg_mem))
+    {
+      __set_errno (EINVAL);
+      return -1;
+    }
+
   _IO_flockfile (stream);
 
   if (fprintf (stream, "%s:%s:", g->sg_namp, _S (g->sg_passwd)) < 0)
diff --git a/gshadow/tst-putsgent.c b/gshadow/tst-putsgent.c
new file mode 100644
index 0000000000..5b0f381bc5
--- /dev/null
+++ b/gshadow/tst-putsgent.c
@@ -0,0 +1,168 @@
+/* Test for processing of invalid gshadow entries.  [BZ #18724]
+   Copyright (C) 2015 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 <errno.h>
+#include <gshadow.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static bool errors;
+
+static void
+check (struct sgrp e, const char *expected)
+{
+  char *buf;
+  size_t buf_size;
+  FILE *f = open_memstream (&buf, &buf_size);
+
+  if (f == NULL)
+    {
+      printf ("open_memstream: %m\n");
+      errors = true;
+      return;
+    }
+
+  int ret = putsgent (&e, f);
+
+  if (expected == NULL)
+    {
+      if (ret == -1)
+	{
+	  if (errno != EINVAL)
+	    {
+	      printf ("putsgent: unexpected error code: %m\n");
+	      errors = true;
+	    }
+	}
+      else
+	{
+	  printf ("putsgent: unexpected success (\"%s\")\n", e.sg_namp);
+	  errors = true;
+	}
+    }
+  else
+    {
+      /* Expect success.  */
+      size_t expected_length = strlen (expected);
+      if (ret == 0)
+	{
+	  long written = ftell (f);
+
+	  if (written <= 0 || fflush (f) < 0)
+	    {
+	      printf ("stream error: %m\n");
+	      errors = true;
+	    }
+	  else if (buf[written - 1] != '\n')
+	    {
+	      printf ("FAILED: \"%s\" without newline\n", expected);
+	      errors = true;
+	    }
+	  else if (strncmp (buf, expected, written - 1) != 0
+		   || written - 1 != expected_length)
+	    {
+	      printf ("FAILED: \"%s\" (%ld), expected \"%s\" (%zu)\n",
+		      buf, written - 1, expected, expected_length);
+	      errors = true;
+	    }
+	}
+      else
+	{
+	  printf ("FAILED: putsgent (expected \"%s\"): %m\n", expected);
+	  errors = true;
+	}
+    }
+
+  fclose (f);
+  free (buf);
+}
+
+static int
+do_test (void)
+{
+  check ((struct sgrp) {
+      .sg_namp = (char *) "root",
+    },
+    "root:::");
+  check ((struct sgrp) {
+      .sg_namp = (char *) "root",
+      .sg_passwd = (char *) "password",
+    },
+    "root:password::");
+  check ((struct sgrp) {
+      .sg_namp = (char *) "root",
+      .sg_passwd = (char *) "password",
+      .sg_adm = (char *[]) {(char *) "adm1", (char *) "adm2", NULL},
+      .sg_mem = (char *[]) {(char *) "mem1", (char *) "mem2", NULL},
+    },
+    "root:password:adm1,adm2:mem1,mem2");
+
+  /* Bad values.  */
+  {
+    static const char *const bad_strings[] = {
+      ":",
+      "\n",
+      ":bad",
+      "\nbad",
+      "b:ad",
+      "b\nad",
+      "bad:",
+      "bad\n",
+      "b:a\nd",
+      ",",
+      "\n,",
+      ":,",
+      ",bad",
+      "b,ad",
+      "bad,",
+      NULL
+    };
+    for (const char *const *bad = bad_strings; *bad != NULL; ++bad)
+      {
+	char *members[]
+	  = {(char *) "first", (char *) *bad, (char *) "last", NULL};
+	if (strpbrk (*bad, ":\n") != NULL)
+	  {
+	    check ((struct sgrp) {
+		.sg_namp = (char *) *bad,
+	      }, NULL);
+	    check ((struct sgrp) {
+		.sg_namp = (char *) "root",
+		.sg_passwd = (char *) *bad,
+	      }, NULL);
+	  }
+	check ((struct sgrp) {
+	    .sg_namp = (char *) "root",
+	    .sg_passwd = (char *) "password",
+	    .sg_adm = members
+	  }, NULL);
+	check ((struct sgrp) {
+	    .sg_namp = (char *) "root",
+	    .sg_passwd = (char *) "password",
+	    .sg_mem = members
+	  }, NULL);
+      }
+  }
+
+  return errors;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/include/nss.h b/include/nss.h
index 0541335c18..1e8cc3910d 100644
--- a/include/nss.h
+++ b/include/nss.h
@@ -1 +1,14 @@
+#ifndef _NSS_H
 #include <nss/nss.h>
+
+#define NSS_INVALID_FIELD_CHARACTERS ":\n"
+extern const char __nss_invalid_field_characters[] attribute_hidden;
+
+_Bool __nss_valid_field (const char *value)
+  attribute_hidden internal_function;
+_Bool __nss_valid_list_field (char **list)
+  attribute_hidden internal_function;
+const char *__nss_rewrite_field (const char *value, char **to_be_freed)
+  attribute_hidden internal_function;
+
+#endif /* _NSS_H */
diff --git a/include/pwd.h b/include/pwd.h
index bd7fecc16e..3b0f72540c 100644
--- a/include/pwd.h
+++ b/include/pwd.h
@@ -24,7 +24,7 @@ extern int __fgetpwent_r (FILE * __stream, struct passwd *__resultbuf,
 			  char *__buffer, size_t __buflen,
 			  struct passwd **__result);
 
-#include <nss/nss.h>
+#include <nss.h>
 
 struct parser_data;
 extern int _nss_files_parse_pwent (char *line, struct passwd *result,
diff --git a/nss/Makefile b/nss/Makefile
index 02a50160cb..bbbad85d7e 100644
--- a/nss/Makefile
+++ b/nss/Makefile
@@ -26,6 +26,7 @@ headers			:= nss.h
 
 # This is the trivial part which goes into libc itself.
 routines		= nsswitch getnssent getnssent_r digits_dots \
+			  valid_field valid_list_field rewrite_field \
 			  $(addsuffix -lookup,$(databases))
 
 # These are the databases that go through nss dispatch.
@@ -47,8 +48,10 @@ install-bin             := getent makedb
 makedb-modules = xmalloc hash-string
 extra-objs		+= $(makedb-modules:=.o)
 
+tests-static            = tst-field
 tests			= test-netdb tst-nss-test1 test-digits-dots \
-			  tst-nss-getpwent bug17079
+			  tst-nss-getpwent bug17079 \
+			  $(tests-static)
 xtests			= bug-erange
 
 # Specify rules for the nss_* modules.  We have some services.
@@ -83,8 +86,7 @@ libnss_db-inhibit-o	= $(filter-out .os,$(object-suffixes))
 ifeq ($(build-static-nss),yes)
 routines                += $(libnss_files-routines)
 static-only-routines    += $(libnss_files-routines)
-tests-static		= tst-nss-static
-tests			+= $(tests-static)
+tests-static		+= tst-nss-static
 endif
 
 include ../Rules
diff --git a/nss/getent.c b/nss/getent.c
index 34df8487a9..996d378af7 100644
--- a/nss/getent.c
+++ b/nss/getent.c
@@ -184,20 +184,8 @@ ethers_keys (int number, char *key[])
 static void
 print_group (struct group *grp)
 {
-  unsigned int i = 0;
-
-  printf ("%s:%s:%lu:", grp->gr_name ? grp->gr_name : "",
-	  grp->gr_passwd ? grp->gr_passwd : "",
-	  (unsigned long int) grp->gr_gid);
-
-  while (grp->gr_mem[i] != NULL)
-    {
-      fputs_unlocked (grp->gr_mem[i], stdout);
-      ++i;
-      if (grp->gr_mem[i] != NULL)
-	putchar_unlocked (',');
-    }
-  putchar_unlocked ('\n');
+  if (putgrent (grp, stdout) != 0)
+    fprintf (stderr, "error writing group entry: %m\n");
 }
 
 static int
@@ -241,32 +229,8 @@ group_keys (int number, char *key[])
 static void
 print_gshadow (struct sgrp *sg)
 {
-  unsigned int i = 0;
-
-  printf ("%s:%s:",
-	  sg->sg_namp ? sg->sg_namp : "",
-	  sg->sg_passwd ? sg->sg_passwd : "");
-
-  while (sg->sg_adm[i] != NULL)
-    {
-      fputs_unlocked (sg->sg_adm[i], stdout);
-      ++i;
-      if (sg->sg_adm[i] != NULL)
-	putchar_unlocked (',');
-    }
-
-  putchar_unlocked (':');
-
-  i = 0;
-  while (sg->sg_mem[i] != NULL)
-    {
-      fputs_unlocked (sg->sg_mem[i], stdout);
-      ++i;
-      if (sg->sg_mem[i] != NULL)
-	putchar_unlocked (',');
-    }
-
-  putchar_unlocked ('\n');
+  if (putsgent (sg, stdout) != 0)
+    fprintf (stderr, "error writing gshadow entry: %m\n");
 }
 
 static int
@@ -603,14 +567,8 @@ networks_keys (int number, char *key[])
 static void
 print_passwd (struct passwd *pwd)
 {
-  printf ("%s:%s:%lu:%lu:%s:%s:%s\n",
-	  pwd->pw_name ? pwd->pw_name : "",
-	  pwd->pw_passwd ? pwd->pw_passwd : "",
-	  (unsigned long int) pwd->pw_uid,
-	  (unsigned long int) pwd->pw_gid,
-	  pwd->pw_gecos ? pwd->pw_gecos : "",
-	  pwd->pw_dir ? pwd->pw_dir : "",
-	  pwd->pw_shell ? pwd->pw_shell : "");
+  if (putpwent (pwd, stdout) != 0)
+    fprintf (stderr, "error writing passwd entry: %m\n");
 }
 
 static int
@@ -812,26 +770,8 @@ services_keys (int number, char *key[])
 static void
 print_shadow (struct spwd *sp)
 {
-  printf ("%s:%s:",
-	  sp->sp_namp ? sp->sp_namp : "",
-	  sp->sp_pwdp ? sp->sp_pwdp : "");
-
-#define SHADOW_FIELD(n) \
-  if (sp->n == -1)							      \
-    putchar_unlocked (':');						      \
-  else									      \
-    printf ("%ld:", sp->n)
-
-  SHADOW_FIELD (sp_lstchg);
-  SHADOW_FIELD (sp_min);
-  SHADOW_FIELD (sp_max);
-  SHADOW_FIELD (sp_warn);
-  SHADOW_FIELD (sp_inact);
-  SHADOW_FIELD (sp_expire);
-  if (sp->sp_flag == ~0ul)
-    putchar_unlocked ('\n');
-  else
-    printf ("%lu\n", sp->sp_flag);
+  if (putspent (sp, stdout) != 0)
+    fprintf (stderr, "error writing shadow entry: %m\n");
 }
 
 static int
diff --git a/nss/rewrite_field.c b/nss/rewrite_field.c
new file mode 100644
index 0000000000..fb9d274842
--- /dev/null
+++ b/nss/rewrite_field.c
@@ -0,0 +1,51 @@
+/* Copyright (C) 2015 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 <nss.h>
+#include <string.h>
+
+/* Rewrite VALUE to a valid field value in the NSS database.  Invalid
+   characters are replaced with a single space character ' '.  If
+   VALUE is NULL, the empty string is returned.  *TO_BE_FREED is
+   overwritten with a pointer the caller has to free if the function
+   returns successfully.  On failure, return NULL.  */
+const char *
+__nss_rewrite_field (const char *value, char **to_be_freed)
+{
+  *to_be_freed = NULL;
+  if (value == NULL)
+    return "";
+
+  /* Search for non-allowed characters.  */
+  const char *p = strpbrk (value, __nss_invalid_field_characters);
+  if (p == NULL)
+    return value;
+  *to_be_freed = __strdup (value);
+  if (*to_be_freed == NULL)
+    return NULL;
+
+  /* Switch pointer to freshly-allocated buffer.  */
+  char *bad = *to_be_freed + (p - value);
+  do
+    {
+      *bad = ' ';
+      bad = strpbrk (bad + 1, __nss_invalid_field_characters);
+    }
+  while (bad != NULL);
+
+  return *to_be_freed;
+}
diff --git a/nss/tst-field.c b/nss/tst-field.c
new file mode 100644
index 0000000000..f97d3aed9b
--- /dev/null
+++ b/nss/tst-field.c
@@ -0,0 +1,101 @@
+/* Test for invalid field handling in file-style NSS databases.  [BZ #18724]
+   Copyright (C) 2015 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/>.  */
+
+/* This test needs to be statically linked because it access hidden
+   functions.  */
+
+#include <nss.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static bool errors;
+
+static void
+check (const char *what, bool expr)
+{
+  if (!expr)
+    {
+      printf ("FAIL: %s\n", what);
+      errors = true;
+    }
+}
+
+#define CHECK(expr) check (#expr, (expr))
+
+static void
+check_rewrite (const char *input, const char *expected)
+{
+  char *to_free;
+  const char *result = __nss_rewrite_field (input, &to_free);
+  CHECK (result != NULL);
+  if (result != NULL && strcmp (result, expected) != 0)
+    {
+      printf ("FAIL: rewrite \"%s\" -> \"%s\", expected \"%s\"\n",
+	      input, result, expected);
+      errors = true;
+    }
+  free (to_free);
+}
+
+static int
+do_test (void)
+{
+  CHECK (__nss_valid_field (NULL));
+  CHECK (__nss_valid_field (""));
+  CHECK (__nss_valid_field ("+"));
+  CHECK (__nss_valid_field ("-"));
+  CHECK (__nss_valid_field (" "));
+  CHECK (__nss_valid_field ("abcdef"));
+  CHECK (__nss_valid_field ("abc def"));
+  CHECK (__nss_valid_field ("abc\tdef"));
+  CHECK (!__nss_valid_field ("abcdef:"));
+  CHECK (!__nss_valid_field ("abcde:f"));
+  CHECK (!__nss_valid_field (":abcdef"));
+  CHECK (!__nss_valid_field ("abcdef\n"));
+  CHECK (!__nss_valid_field ("\nabcdef"));
+  CHECK (!__nss_valid_field (":"));
+  CHECK (!__nss_valid_field ("\n"));
+
+  CHECK (__nss_valid_list_field (NULL));
+  CHECK (__nss_valid_list_field ((char *[]) {(char *) "good", NULL}));
+  CHECK (!__nss_valid_list_field ((char *[]) {(char *) "g,ood", NULL}));
+  CHECK (!__nss_valid_list_field ((char *[]) {(char *) "g\nood", NULL}));
+  CHECK (!__nss_valid_list_field ((char *[]) {(char *) "g:ood", NULL}));
+
+  check_rewrite (NULL, "");
+  check_rewrite ("", "");
+  check_rewrite ("abc", "abc");
+  check_rewrite ("abc\n", "abc ");
+  check_rewrite ("abc:", "abc ");
+  check_rewrite ("\nabc", " abc");
+  check_rewrite (":abc", " abc");
+  check_rewrite (":", " ");
+  check_rewrite ("\n", " ");
+  check_rewrite ("a:b:c", "a b c");
+  check_rewrite ("a\nb\nc", "a b c");
+  check_rewrite ("a\nb:c", "a b c");
+  check_rewrite ("aa\nbb\ncc", "aa bb cc");
+  check_rewrite ("aa\nbb:cc", "aa bb cc");
+
+  return errors;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/nss/valid_field.c b/nss/valid_field.c
new file mode 100644
index 0000000000..5fcddc50ae
--- /dev/null
+++ b/nss/valid_field.c
@@ -0,0 +1,31 @@
+/* Copyright (C) 2015 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 <nss.h>
+#include <string.h>
+
+const char __nss_invalid_field_characters[] = NSS_INVALID_FIELD_CHARACTERS;
+
+/* Check that VALUE is either NULL or a NUL-terminated string which
+   does not contain characters not permitted in NSS database
+   fields.  */
+_Bool
+__nss_valid_field (const char *value)
+{
+  return value == NULL
+    || strpbrk (value, __nss_invalid_field_characters) == NULL;
+}
diff --git a/nss/valid_list_field.c b/nss/valid_list_field.c
new file mode 100644
index 0000000000..98ab93beab
--- /dev/null
+++ b/nss/valid_list_field.c
@@ -0,0 +1,35 @@
+/* Copyright (C) 2015 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 <nss.h>
+#include <stdbool.h>
+#include <string.h>
+
+static const char invalid_characters[] = NSS_INVALID_FIELD_CHARACTERS ",";
+
+/* Check that all list members match the field syntax requirements and
+   do not contain the character ','.  */
+_Bool
+__nss_valid_list_field (char **list)
+{
+  if (list == NULL)
+    return true;
+  for (; *list != NULL; ++list)
+    if (strpbrk (*list, invalid_characters) != NULL)
+      return false;
+  return true;
+}
diff --git a/pwd/Makefile b/pwd/Makefile
index 7f6de03b57..af0973455b 100644
--- a/pwd/Makefile
+++ b/pwd/Makefile
@@ -28,7 +28,7 @@ routines := fgetpwent getpw putpwent \
 	    getpwent getpwnam getpwuid \
 	    getpwent_r getpwnam_r getpwuid_r fgetpwent_r
 
-tests := tst-getpw
+tests := tst-getpw tst-putpwent
 
 include ../Rules
 
diff --git a/pwd/putpwent.c b/pwd/putpwent.c
index 8be58c27ae..16b9c6f80f 100644
--- a/pwd/putpwent.c
+++ b/pwd/putpwent.c
@@ -18,37 +18,47 @@
 #include <errno.h>
 #include <stdio.h>
 #include <pwd.h>
+#include <nss.h>
 
 #define _S(x)	x ?: ""
 
-/* Write an entry to the given stream.
-   This must know the format of the password file.  */
+/* Write an entry to the given stream.  This must know the format of
+   the password file.  If the input contains invalid characters,
+   return EINVAL, or replace them with spaces (if they are contained
+   in the GECOS field).  */
 int
-putpwent (p, stream)
-     const struct passwd *p;
-     FILE *stream;
+putpwent (const struct passwd *p, FILE *stream)
 {
-  if (p == NULL || stream == NULL)
+  if (p == NULL || stream == NULL
+      || p->pw_name == NULL || !__nss_valid_field (p->pw_name)
+      || !__nss_valid_field (p->pw_passwd)
+      || !__nss_valid_field (p->pw_dir)
+      || !__nss_valid_field (p->pw_shell))
     {
       __set_errno (EINVAL);
       return -1;
     }
 
+  int ret;
+  char *gecos_alloc;
+  const char *gecos = __nss_rewrite_field (p->pw_gecos, &gecos_alloc);
+
+  if (gecos == NULL)
+    return -1;
+
   if (p->pw_name[0] == '+' || p->pw_name[0] == '-')
-    {
-      if (fprintf (stream, "%s:%s:::%s:%s:%s\n",
-		   p->pw_name, _S (p->pw_passwd),
-		   _S (p->pw_gecos), _S (p->pw_dir), _S (p->pw_shell)) < 0)
-	return -1;
-    }
+      ret = fprintf (stream, "%s:%s:::%s:%s:%s\n",
+		     p->pw_name, _S (p->pw_passwd),
+		     gecos, _S (p->pw_dir), _S (p->pw_shell));
   else
-    {
-      if (fprintf (stream, "%s:%s:%lu:%lu:%s:%s:%s\n",
-		   p->pw_name, _S (p->pw_passwd),
-		   (unsigned long int) p->pw_uid,
-		   (unsigned long int) p->pw_gid,
-		   _S (p->pw_gecos), _S (p->pw_dir), _S (p->pw_shell)) < 0)
-	return -1;
-    }
-  return 0;
+      ret = fprintf (stream, "%s:%s:%lu:%lu:%s:%s:%s\n",
+		     p->pw_name, _S (p->pw_passwd),
+		     (unsigned long int) p->pw_uid,
+		     (unsigned long int) p->pw_gid,
+		     gecos, _S (p->pw_dir), _S (p->pw_shell));
+
+  free (gecos_alloc);
+  if (ret >= 0)
+    ret = 0;
+  return ret;
 }
diff --git a/pwd/tst-putpwent.c b/pwd/tst-putpwent.c
new file mode 100644
index 0000000000..a408e43e3b
--- /dev/null
+++ b/pwd/tst-putpwent.c
@@ -0,0 +1,168 @@
+/* Test for processing of invalid passwd entries.  [BZ #18724]
+   Copyright (C) 2015 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 <errno.h>
+#include <pwd.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+static bool errors;
+
+static void
+check (struct passwd p, const char *expected)
+{
+  char *buf;
+  size_t buf_size;
+  FILE *f = open_memstream (&buf, &buf_size);
+
+  if (f == NULL)
+    {
+      printf ("open_memstream: %m\n");
+      errors = true;
+      return;
+    }
+
+  int ret = putpwent (&p, f);
+
+  if (expected == NULL)
+    {
+      if (ret == -1)
+	{
+	  if (errno != EINVAL)
+	    {
+	      printf ("putpwent: unexpected error code: %m\n");
+	      errors = true;
+	    }
+	}
+      else
+	{
+	  printf ("putpwent: unexpected success (\"%s\")\n", p.pw_name);
+	  errors = true;
+	}
+    }
+  else
+    {
+      /* Expect success.  */
+      size_t expected_length = strlen (expected);
+      if (ret == 0)
+	{
+	  long written = ftell (f);
+
+	  if (written <= 0 || fflush (f) < 0)
+	    {
+	      printf ("stream error: %m\n");
+	      errors = true;
+	    }
+	  else if (buf[written - 1] != '\n')
+	    {
+	      printf ("FAILED: \"%s\" without newline\n", expected);
+	      errors = true;
+	    }
+	  else if (strncmp (buf, expected, written - 1) != 0
+		   || written - 1 != expected_length)
+	    {
+	      printf ("FAILED: \"%s\" (%ld), expected \"%s\" (%zu)\n",
+		      buf, written - 1, expected, expected_length);
+	      errors = true;
+	    }
+	}
+      else
+	{
+	  printf ("FAILED: putpwent (expected \"%s\"): %m\n", expected);
+	  errors = true;
+	}
+    }
+
+  fclose (f);
+  free (buf);
+}
+
+static int
+do_test (void)
+{
+  check ((struct passwd) {
+      .pw_name = (char *) "root",
+    },
+    "root::0:0:::");
+  check ((struct passwd) {
+      .pw_name = (char *) "root",
+      .pw_passwd = (char *) "password",
+    },
+    "root:password:0:0:::");
+  check ((struct passwd) {
+      .pw_name = (char *) "root",
+      .pw_passwd = (char *) "password",
+      .pw_uid = 12,
+      .pw_gid = 34,
+      .pw_gecos = (char *) "gecos",
+      .pw_dir = (char *) "home",
+      .pw_shell = (char *) "shell",
+    },
+    "root:password:12:34:gecos:home:shell");
+  check ((struct passwd) {
+      .pw_name = (char *) "root",
+      .pw_passwd = (char *) "password",
+      .pw_uid = 12,
+      .pw_gid = 34,
+      .pw_gecos = (char *) ":ge\n:cos\n",
+      .pw_dir = (char *) "home",
+      .pw_shell = (char *) "shell",
+    },
+    "root:password:12:34: ge  cos :home:shell");
+
+  /* Bad values.  */
+  {
+    static const char *const bad_strings[] = {
+      ":",
+      "\n",
+      ":bad",
+      "\nbad",
+      "b:ad",
+      "b\nad",
+      "bad:",
+      "bad\n",
+      "b:a\nd",
+      NULL
+    };
+    for (const char *const *bad = bad_strings; *bad != NULL; ++bad)
+      {
+	check ((struct passwd) {
+	    .pw_name = (char *) *bad,
+	  }, NULL);
+	check ((struct passwd) {
+	    .pw_name = (char *) "root",
+	    .pw_passwd = (char *) *bad,
+	  }, NULL);
+	check ((struct passwd) {
+	    .pw_name = (char *) "root",
+	    .pw_dir = (char *) *bad,
+	  }, NULL);
+	check ((struct passwd) {
+	    .pw_name = (char *) "root",
+	    .pw_shell = (char *) *bad,
+	  }, NULL);
+      }
+  }
+
+  return errors > 0;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/shadow/Makefile b/shadow/Makefile
index 8291c61622..6990f339f7 100644
--- a/shadow/Makefile
+++ b/shadow/Makefile
@@ -27,7 +27,7 @@ routines	= getspent getspnam sgetspent fgetspent putspent \
 		  getspent_r getspnam_r sgetspent_r fgetspent_r \
 		  lckpwdf
 
-tests = tst-shadow
+tests = tst-shadow tst-putspent
 
 CFLAGS-getspent_r.c = -fexceptions
 CFLAGS-getspent.c = -fexceptions
diff --git a/shadow/putspent.c b/shadow/putspent.c
index 142e697e64..ba8230a482 100644
--- a/shadow/putspent.c
+++ b/shadow/putspent.c
@@ -15,6 +15,8 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
+#include <errno.h>
+#include <nss.h>
 #include <stdio.h>
 #include <shadow.h>
 
@@ -31,6 +33,13 @@ putspent (const struct spwd *p, FILE *stream)
 {
   int errors = 0;
 
+  if (p->sp_namp == NULL || !__nss_valid_field (p->sp_namp)
+      || !__nss_valid_field (p->sp_pwdp))
+    {
+      __set_errno (EINVAL);
+      return -1;
+    }
+
   flockfile (stream);
 
   if (fprintf (stream, "%s:%s:", p->sp_namp, _S (p->sp_pwdp)) < 0)
diff --git a/shadow/tst-putspent.c b/shadow/tst-putspent.c
new file mode 100644
index 0000000000..d00c0229fc
--- /dev/null
+++ b/shadow/tst-putspent.c
@@ -0,0 +1,164 @@
+/* Test for processing of invalid shadow entries.  [BZ #18724]
+   Copyright (C) 2015 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 <errno.h>
+#include <shadow.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static bool errors;
+
+static void
+check (struct spwd p, const char *expected)
+{
+  char *buf;
+  size_t buf_size;
+  FILE *f = open_memstream (&buf, &buf_size);
+
+  if (f == NULL)
+    {
+      printf ("open_memstream: %m\n");
+      errors = true;
+      return;
+    }
+
+  int ret = putspent (&p, f);
+
+  if (expected == NULL)
+    {
+      if (ret == -1)
+	{
+	  if (errno != EINVAL)
+	    {
+	      printf ("putspent: unexpected error code: %m\n");
+	      errors = true;
+	    }
+	}
+      else
+	{
+	  printf ("putspent: unexpected success (\"%s\")\n", p.sp_namp);
+	  errors = true;
+	}
+    }
+  else
+    {
+      /* Expect success.  */
+      size_t expected_length = strlen (expected);
+      if (ret == 0)
+	{
+	  long written = ftell (f);
+
+	  if (written <= 0 || fflush (f) < 0)
+	    {
+	      printf ("stream error: %m\n");
+	      errors = true;
+	    }
+	  else if (buf[written - 1] != '\n')
+	    {
+	      printf ("FAILED: \"%s\" without newline\n", expected);
+	      errors = true;
+	    }
+	  else if (strncmp (buf, expected, written - 1) != 0
+		   || written - 1 != expected_length)
+	    {
+	      printf ("FAILED: \"%s\" (%ld), expected \"%s\" (%zu)\n",
+		      buf, written - 1, expected, expected_length);
+	      errors = true;
+	    }
+	}
+      else
+	{
+	  printf ("FAILED: putspent (expected \"%s\"): %m\n", expected);
+	  errors = true;
+	}
+    }
+
+  fclose (f);
+  free (buf);
+}
+
+static int
+do_test (void)
+{
+  check ((struct spwd) {
+      .sp_namp = (char *) "root",
+    },
+    "root::0:0:0:0:0:0:0");
+  check ((struct spwd) {
+      .sp_namp = (char *) "root",
+      .sp_pwdp = (char *) "password",
+    },
+    "root:password:0:0:0:0:0:0:0");
+  check ((struct spwd) {
+      .sp_namp = (char *) "root",
+      .sp_pwdp = (char *) "password",
+      .sp_lstchg = -1,
+      .sp_min = -1,
+      .sp_max = -1,
+      .sp_warn = -1,
+      .sp_inact = -1,
+      .sp_expire = -1,
+      .sp_flag = -1
+    },
+    "root:password:::::::");
+  check ((struct spwd) {
+      .sp_namp = (char *) "root",
+      .sp_pwdp = (char *) "password",
+      .sp_lstchg = 1,
+      .sp_min = 2,
+      .sp_max = 3,
+      .sp_warn = 4,
+      .sp_inact = 5,
+      .sp_expire = 6,
+      .sp_flag = 7
+    },
+    "root:password:1:2:3:4:5:6:7");
+
+  /* Bad values.  */
+  {
+    static const char *const bad_strings[] = {
+      ":",
+      "\n",
+      ":bad",
+      "\nbad",
+      "b:ad",
+      "b\nad",
+      "bad:",
+      "bad\n",
+      "b:a\nd",
+      NULL
+    };
+    for (const char *const *bad = bad_strings; *bad != NULL; ++bad)
+      {
+	check ((struct spwd) {
+	    .sp_namp = (char *) *bad,
+	  }, NULL);
+	check ((struct spwd) {
+	    .sp_namp = (char *) "root",
+	    .sp_pwdp = (char *) *bad,
+	  }, NULL);
+      }
+  }
+
+  return errors;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"