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 '+'.

1 files changed, 168 insertions, 0 deletions

diff --git a/pwd/tst-putpwent.c b/pwd/tst-putpwent.c
new file mode 100644
index 0000000..a408e43
--- /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"