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, 180 insertions, 1 deletions

diff --git a/gshadow/Makefile b/gshadow/Makefile
index 883e1c8..c811041 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 0b2cad6..c1cb921 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 0000000..5b0f381
--- /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"