NSS: Replace exported NSS lookup functions with stubs [BZ #21962]

Commit 384ca551743318bd9c9e24a496d6397f2e3f2a49 from 2007 added this to
nss/XXX-lookup.c:

+#ifndef NO_COMPAT
+int
+internal_function attribute_compat_text_section
+DB_COMPAT_FCT (service_user **ni, const char *fct_name, void **fctp)
+{
+  return DB_LOOKUP_FCT (ni, fct_name, NULL, fctp);
+}
+#endif

That is, it adds a pseudo-compat function with an internal_function
attribute.  The function it was supposed to replace did not have the
attribute:

 extern int DB_LOOKUP_FCT (service_user **ni, const char *fct_name,
-			  void **fctp) internal_function;
+			  const char *fct2_name, void **fctp)
+  internal_function;

This changed the calling convention on i386 for the following
functions in the public ABI:

  __nss_passwd_lookup
  __nss_group_lookup
  __nss_hosts_lookup

This commit replaces the functions with always-failing stubs,
with true compat symbols.  Due to a happy accident, the calling
convention of the stub is identical for the internal_function
and non-internal_function case on i386.

In addition, this commit auto-generates the __nss_*_lookup2
function declarations as part of <nsswitch.h>.

1 files changed, 42 insertions, 0 deletions

diff --git a/nss/compat-lookup.c b/nss/compat-lookup.c
new file mode 100644
index 0000000..b5c9673
--- /dev/null
+++ b/nss/compat-lookup.c
@@ -0,0 +1,42 @@
+/* Compatibility stubs of accidentally exported __nss_*_lookup functions.
+   Copyright (C) 2017 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 <shlib-compat.h>
+#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_27)
+
+# include <errno.h>
+# include <nsswitch.h>
+
+/* On i386, the function calling convention changed from the standard
+   ABI calling convention to three register parameters in glibc 2.8.
+   The following error-returning stub happens to be compatible with
+   glibc 2.7 and earlier and glibc 2.8 and later, even on i386.  */
+int
+attribute_compat_text_section
+__nss_passwd_lookup (service_user **ni, const char *fct_name, void **fctp)
+{
+  __set_errno (ENOSYS);
+  return -1;
+}
+compat_symbol (libc, __nss_passwd_lookup, __nss_passwd_lookup, GLIBC_2_0);
+strong_alias (__nss_passwd_lookup, __nss_group_lookup)
+compat_symbol (libc, __nss_group_lookup, __nss_group_lookup, GLIBC_2_0);
+strong_alias (__nss_passwd_lookup, __nss_hosts_lookup)
+compat_symbol (libc, __nss_hosts_lookup, __nss_hosts_lookup, GLIBC_2_0);
+
+#endif /* SHLIB_COMPAT */