Re: internal_function symbols part of the public ABI

[Florian Weimer <fweimer at redhat dot com>]

On 08/14/2017 04:37 PM, Andreas Schwab wrote:
> On Aug 14 2017, Florian Weimer <fweimer@redhat.com> wrote:
> 
>> The 2007 commit radically changed the calling convention, so it's safe
>> to assume that there were no active users on i386 at the time because
>> they would have run into crashes.  Today, it's still difficult to call
>> these functions because it is hard to write a correct prototype.
> 
> They are really private interfaces for nscd, AFAICS.
> 
>> Can we remove the functions completely?
> 
> They should be unexported, for sure.  Since nscd doesn't use them any
> more, they could just be dummies.

What about the attached patch?

I cleaned up the declarations of the __nss_*_lookup* functions.  They
are now generated from databases.def in <nsswitch.h>.  I switched all
the internal users of the *lookup functions to *lookup2 functions, so
that the compat functions are not used internally anymore.

Thanks,
Florian

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>.

2017-08-14  Florian Weimer  <fweimer@redhat.com>

	[BZ #21962]
	NSS: Create stubs for accidentally exported lookup functions.
	* grp/initgroups.c (__nss_group_lookup, __nss_lookup_function):
	Remove declaration.
	* inet/ether_hton.c (__nss_ethers_lookup): Likewise.
	(ether_hostton): Call __nss_ethers_lookup2 instead.
	* inet/ether_ntoh.c (__nss_ethers_lookup): Remove declaration.
	(ether_ntohost): Call __nss_ethers_lookup2 instead.
	* inet/getnetgrent_r.c (__nss_netgroup_lookup): Remove declaration.
	(setup): Call __nss_netgroup_lookup2 instead.
	* nss/Makefile (routines): Add compat-lookup.
	* nss/Versions (GLIBC_2.27): Add symbol version.
	* nss/XXX-lookup (DB_LOOKUP_FCT): Remove declaration.  Now provided by <nsswitch.h>.
	(DB_COMPAT_FCT): Remove.
	* nss/compat-lookup.c: New file.
	* nss/nsswitch.h: Generate __nss_*_lookup2 function prototypes
	from databases.def.
	* nss/service-lookup.c (NO_COMPAT): Remove definition.
	* sunrpc/netname.c (__nss_publickey_lookup): Remove declaration.
	(netname2user): Call __nss_publickey_lookup2 instead.
	* sunrpc/publickey.c (__nss_publickey_lookup): Remove declaration.
	(getpublickey, getsecretkey): Call __nss_publickey_lookup2
	instead.

diff --git a/grp/initgroups.c b/grp/initgroups.c
index 7a40813d5e..0d5b841796 100644
--- a/grp/initgroups.c
+++ b/grp/initgroups.c
@@ -36,11 +36,6 @@ typedef enum nss_status (*initgroups_dyn_function) (const char *, gid_t,
 						    long int *, long int *,
 						    gid_t **, long int, int *);
 
-/* The lookup function for the first entry of this service.  */
-extern int __nss_group_lookup (service_user **nip, const char *name,
-				   void **fctp);
-extern void *__nss_lookup_function (service_user *ni, const char *fct_name);
-
 extern service_user *__nss_group_database attribute_hidden;
 service_user *__nss_initgroups_database;
 static bool use_initgroups_entry;
diff --git a/inet/ether_hton.c b/inet/ether_hton.c
index a5523986c9..164838ecec 100644
--- a/inet/ether_hton.c
+++ b/inet/ether_hton.c
@@ -27,11 +27,6 @@
 typedef int (*lookup_function) (const char *, struct etherent *, char *, int,
 				int *);
 
-/* The lookup function for the first entry of this service.  */
-extern int __nss_ethers_lookup (service_user **nip, const char *name,
-				void **fctp) internal_function;
-
-
 int
 ether_hostton (const char *hostname, struct ether_addr *addr)
 {
@@ -49,7 +44,7 @@ ether_hostton (const char *hostname, struct ether_addr *addr)
 
   if (startp == NULL)
     {
-      no_more = __nss_ethers_lookup (&nip, "gethostton_r", &fct.ptr);
+      no_more = __nss_ethers_lookup2 (&nip, "gethostton_r", NULL, &fct.ptr);
       if (no_more)
 	startp = (service_user *) -1;
       else
diff --git a/inet/ether_ntoh.c b/inet/ether_ntoh.c
index b2f7422ace..393601ee7a 100644
--- a/inet/ether_ntoh.c
+++ b/inet/ether_ntoh.c
@@ -28,11 +28,6 @@
 typedef int (*lookup_function) (const struct ether_addr *, struct etherent *,
 				char *, size_t, int *);
 
-/* The lookup function for the first entry of this service.  */
-extern int __nss_ethers_lookup (service_user **nip, const char *name,
-				void **fctp) internal_function;
-
-
 int
 ether_ntohost (char *hostname, const struct ether_addr *addr)
 {
@@ -50,7 +45,7 @@ ether_ntohost (char *hostname, const struct ether_addr *addr)
 
   if (startp == NULL)
     {
-      no_more = __nss_ethers_lookup (&nip, "getntohost_r", &fct.ptr);
+      no_more = __nss_ethers_lookup2 (&nip, "getntohost_r", NULL, &fct.ptr);
       if (no_more)
 	startp = (service_user *) -1;
       else
diff --git a/inet/getnetgrent_r.c b/inet/getnetgrent_r.c
index a8fc51c1b6..89fefeb612 100644
--- a/inet/getnetgrent_r.c
+++ b/inet/getnetgrent_r.c
@@ -36,10 +36,6 @@ __libc_lock_define_initialized (static, lock)
    kept in this structure.  */
 static struct __netgrent dataset;
 
-/* The lookup function for the first entry of this service.  */
-extern int __nss_netgroup_lookup (service_user **nipp, const char *name,
-				  void **fctp) internal_function;
-
 /* Set up NIP to run through the services.  Return nonzero if there are no
    services (left).  */
 static int
@@ -54,7 +50,7 @@ setup (void **fctp, service_user **nipp)
     {
       /* Executing this more than once at the same time must yield the
 	 same result every time.  So we need no locking.  */
-      no_more = __nss_netgroup_lookup (nipp, "setnetgrent", fctp);
+      no_more = __nss_netgroup_lookup2 (nipp, "setnetgrent", NULL, fctp);
       startp = no_more ? (service_user *) -1 : *nipp;
 #ifdef PTR_MANGLE
       PTR_MANGLE (startp);
diff --git a/nss/Makefile b/nss/Makefile
index d9f6d41181..1e298c28f1 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 f8ababccc7..50268ed9b5 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 972a2102bf..49417691b2 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 0000000000..b5c9673b49
--- /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 7da90130ec..2b86d63ddb 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 3f230d606a..3b97b419b6 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"
diff --git a/sunrpc/netname.c b/sunrpc/netname.c
index 9aee3e4042..0dacd1cac7 100644
--- a/sunrpc/netname.c
+++ b/sunrpc/netname.c
@@ -140,9 +140,6 @@ libc_hidden_nolink_sunrpc (getnetname, GLIBC_2_1)
 /* Type of the lookup function for netname2user.  */
 typedef int (*netname2user_function) (const char netname[MAXNETNAMELEN + 1],
 				      uid_t *, gid_t *, int *, gid_t *);
-/* The lookup function for the first entry of this service.  */
-extern int __nss_publickey_lookup (service_user ** nip, const char *name,
-				   void **fctp) internal_function;
 
 int
 netname2user (const char netname[MAXNETNAMELEN + 1], uid_t * uidp, gid_t * gidp,
@@ -161,7 +158,7 @@ netname2user (const char netname[MAXNETNAMELEN + 1], uid_t * uidp, gid_t * gidp,
 
   if (startp == NULL)
     {
-      no_more = __nss_publickey_lookup (&nip, "netname2user", &fct.ptr);
+      no_more = __nss_publickey_lookup2 (&nip, "netname2user", NULL, &fct.ptr);
       if (no_more)
 	startp = (service_user *) - 1;
       else
diff --git a/sunrpc/publickey.c b/sunrpc/publickey.c
index ca6e4303d4..e7ac8548f8 100644
--- a/sunrpc/publickey.c
+++ b/sunrpc/publickey.c
@@ -31,11 +31,6 @@ typedef int (*public_function) (const char *, char *, int *);
 /* Type of the lookup function for the secret key.  */
 typedef int (*secret_function) (const char *, char *, const char *, int *);
 
-/* The lookup function for the first entry of this service.  */
-extern int __nss_publickey_lookup (service_user **nip, const char *name,
-				   void **fctp) internal_function;
-
-
 int
 getpublickey (const char *name, char *key)
 {
@@ -52,7 +47,7 @@ getpublickey (const char *name, char *key)
 
   if (startp == NULL)
     {
-      no_more = __nss_publickey_lookup (&nip, "getpublickey", &fct.ptr);
+      no_more = __nss_publickey_lookup2 (&nip, "getpublickey", NULL, &fct.ptr);
       if (no_more)
 	startp = (service_user *) -1;
       else
@@ -95,7 +90,7 @@ getsecretkey (const char *name, char *key, const char *passwd)
 
   if (startp == NULL)
     {
-      no_more = __nss_publickey_lookup (&nip, "getsecretkey", &fct.ptr);
+      no_more = __nss_publickey_lookup2 (&nip, "getsecretkey", NULL, &fct.ptr);
       if (no_more)
 	startp = (service_user *) -1;
       else