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>.

6 files changed, 54 insertions, 17 deletions

diff --git a/nss/Makefile b/nss/Makefile
index d9f6d41..1e298c2 100644
--- a/nss/Makefile
+++ b/nss/Makefile
@@ -27,7 +27,8 @@ headers			:= nss.h
 # This is the trivial part which goes into libc itself.
 routines		= nsswitch getnssent getnssent_r digits_dots \
 			  valid_field valid_list_field rewrite_field \
-			  $(addsuffix -lookup,$(databases))
+			  $(addsuffix -lookup,$(databases)) \
+			  compat-lookup
 
 # These are the databases that go through nss dispatch.
 # Caution: if you add a database here, you must add its real name
diff --git a/nss/Versions b/nss/Versions
index f8ababc..50268ed 100644
--- a/nss/Versions
+++ b/nss/Versions
@@ -7,6 +7,8 @@ libc {
   GLIBC_2.2.2 {
     __nss_hostname_digits_dots;
   }
+  GLIBC_2.27 {
+  }
   GLIBC_PRIVATE {
     _nss_files_parse_grent; _nss_files_parse_pwent; _nss_files_parse_spent;
     __nss_disable_nscd; __nss_lookup_function; _nss_files_parse_sgent;
diff --git a/nss/XXX-lookup.c b/nss/XXX-lookup.c
index 972a210..4941769 100644
--- a/nss/XXX-lookup.c
+++ b/nss/XXX-lookup.c
@@ -34,7 +34,6 @@
 \*******************************************************************/
 
 #define DB_LOOKUP_FCT CONCAT3_1 (__nss_, DATABASE_NAME, _lookup2)
-#define DB_COMPAT_FCT CONCAT3_1 (__nss_, DATABASE_NAME, _lookup)
 #define CONCAT3_1(Pre, Name, Post) CONCAT3_2 (Pre, Name, Post)
 #define CONCAT3_2(Pre, Name, Post) Pre##Name##Post
 
@@ -55,10 +54,6 @@
 
 service_user *DATABASE_NAME_SYMBOL attribute_hidden;
 
-extern int DB_LOOKUP_FCT (service_user **ni, const char *fct_name,
-			  const char *fct2_name, void **fctp);
-libc_hidden_proto (DB_LOOKUP_FCT)
-
 int
 DB_LOOKUP_FCT (service_user **ni, const char *fct_name, const char *fct2_name,
 	       void **fctp)
@@ -73,13 +68,3 @@ DB_LOOKUP_FCT (service_user **ni, const char *fct_name, const char *fct2_name,
   return __nss_lookup (ni, fct_name, fct2_name, fctp);
 }
 libc_hidden_def (DB_LOOKUP_FCT)
-
-
-#ifndef NO_COMPAT
-int
-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
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 */
diff --git a/nss/nsswitch.h b/nss/nsswitch.h
index 7da9013..2b86d63 100644
--- a/nss/nsswitch.h
+++ b/nss/nsswitch.h
@@ -219,4 +219,12 @@ libc_hidden_proto (__nss_hostname_digits_dots)
 #define MAX_NR_ALIASES  48
 #define MAX_NR_ADDRS    48
 
+/* Prototypes for __nss_*_lookup2 functions.  */
+#define DEFINE_DATABASE(arg)				    \
+  int __nss_##arg##_lookup2 (service_user **, const char *, \
+			     const char *, void **);	    \
+  libc_hidden_proto (__nss_##arg##_lookup2)
+#include "databases.def"
+#undef DEFINE_DATABASE
+
 #endif	/* nsswitch.h */
diff --git a/nss/service-lookup.c b/nss/service-lookup.c
index 3f230d6..3b97b41 100644
--- a/nss/service-lookup.c
+++ b/nss/service-lookup.c
@@ -17,6 +17,5 @@
    <http://www.gnu.org/licenses/>.  */
 
 #define DATABASE_NAME services
-#define NO_COMPAT
 
 #include "XXX-lookup.c"