nss_files: Fix /etc/aliases null pointer dereference [BZ #24059]

If /etc/aliases ends with a continuation line (a line that starts
with whitespace) which does not have a trailing newline character,
the file parser would crash due to a null pointer dereference.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

3 files changed, 78 insertions, 0 deletions

diff --git a/nss/Makefile b/nss/Makefile
index 0fa28f0c5e..e66e01d45a 100644
--- a/nss/Makefile
+++ b/nss/Makefile
@@ -68,6 +68,7 @@ tests += tst-nss-files-hosts-erange
 tests += tst-nss-files-hosts-multi
 tests += tst-nss-files-hosts-getent
 tests += tst-nss-files-alias-leak
+tests += tst-nss-files-alias-truncated
 endif
 
 # If we have a thread library then we can test cancellation against
@@ -176,3 +177,4 @@ $(objpfx)tst-nss-files-hosts-multi: $(libdl)
 $(objpfx)tst-nss-files-hosts-getent: $(libdl)
 $(objpfx)tst-nss-files-alias-leak: $(libdl)
 $(objpfx)tst-nss-files-alias-leak.out: $(objpfx)/libnss_files.so
+$(objpfx)tst-nss-files-alias-truncated: $(objpfx)/libnss_files.so
diff --git a/nss/nss_files/files-alias.c b/nss/nss_files/files-alias.c
index 540eb9c678..34d7aa84cc 100644
--- a/nss/nss_files/files-alias.c
+++ b/nss/nss_files/files-alias.c
@@ -333,6 +333,16 @@ get_next_alias (FILE *stream, const char *match, struct aliasent *result,
 		     can be ignored.  */
 		  first_unused[room_left - 1] = '\xff';
 		  line = fgets_unlocked (first_unused, room_left, stream);
+		  if (line == NULL)
+		    {
+		      /* Continuation line without any data and
+			 without a newline at the end.  Treat it as an
+			 empty line and retry, reaching EOF once
+			 more.  */
+		      line = first_unused;
+		      *line = '\0';
+		      continue;
+		    }
 		  if (first_unused[room_left - 1] != '\xff')
 		    goto no_more_room;
 		  cp = strpbrk (line, "#\n");
diff --git a/nss/tst-nss-files-alias-truncated.c b/nss/tst-nss-files-alias-truncated.c
new file mode 100644
index 0000000000..2d6aba3c0e
--- /dev/null
+++ b/nss/tst-nss-files-alias-truncated.c
@@ -0,0 +1,66 @@
+/* Check handling of missing end-of-line at end of /etc/aliases (bug 24059).
+   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 <aliases.h>
+#include <nss.h>
+#include <stddef.h>
+#include <support/check.h>
+#include <support/namespace.h>
+#include <support/test-driver.h>
+#include <support/xunistd.h>
+
+static void
+in_chroot (void *closure)
+{
+  struct support_chroot *chroot_env = closure;
+  xchroot (chroot_env->path_chroot);
+
+  struct aliasent *e = getaliasbyname ("user1");
+  TEST_VERIFY_EXIT (e != NULL);
+  TEST_COMPARE_STRING (e->alias_name, "user1");
+  TEST_COMPARE (e->alias_members_len, 1);
+  TEST_VERIFY_EXIT (e->alias_members != NULL);
+  TEST_COMPARE_STRING (e->alias_members[0], "alias1");
+  TEST_VERIFY (e->alias_local);
+}
+
+static int
+do_test (void)
+{
+  /* nss_files has already been loaded via DT_NEEDED, outside the
+     chroot.  */
+  __nss_configure_lookup ("aliases", "files");
+
+  support_become_root ();
+  if (!support_can_chroot ())
+    return EXIT_UNSUPPORTED;
+
+  struct support_chroot *chroot_env = support_chroot_create
+    ((struct support_chroot_configuration)
+     {
+       .aliases = "user1: alias1,\n"
+        " "              /* Continuation line, but no \n.  */
+     });
+
+  support_isolate_in_subprocess (in_chroot, chroot_env);
+
+  support_chroot_free (chroot_env);
+  return 0;
+}
+
+#include <support/test-driver.c>