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 '+'.

3 files changed, 176 insertions, 8 deletions

diff --git a/grp/Makefile b/grp/Makefile
index c63b552..ed8cc2b 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 e4d662c..1ac7f19 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 0000000..0a07ef6
--- /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"