nss_files: Consolidate file opening in __nss_files_fopen

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

include/nss_files.h

@@ -0,0 +1,28 @@
+/* Internal routines for nss_files.
+   Copyright (C) 2020 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
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _NSS_FILES_H
+#define _NSS_FILES_H
+
+#include <stdio.h>
+
+/* Open PATH for reading, as a data source for nss_files.  */
+FILE *__nss_files_fopen (const char *path);
+libc_hidden_proto (__nss_files_fopen)
+
+#endif /* _NSS_FILES_H */

nss/Makefile

@@ -28,7 +28,7 @@ headers			:= nss.h
 routines		= nsswitch getnssent getnssent_r digits_dots \
 			  valid_field valid_list_field rewrite_field \
 			  $(addsuffix -lookup,$(databases)) \
-			  compat-lookup nss_hash
+			  compat-lookup nss_hash nss_files_fopen
 
 # These are the databases that go through nss dispatch.
 # Caution: if you add a database here, you must add its real name

nss/Versions

@@ -18,6 +18,7 @@ libc {
     __nss_passwd_lookup2; __nss_group_lookup2; __nss_hosts_lookup2;
     __nss_services_lookup2; __nss_next2; __nss_lookup;
     __nss_hash; __nss_database_lookup2;
+    __nss_files_fopen;
   }
 }
 

nss/nss_files/files-XXX.c

@@ -22,6 +22,7 @@
 #include <fcntl.h>
 #include <libc-lock.h>
 #include "nsswitch.h"
+#include <nss_files.h>
 
 #include <kernel-features.h>
 
@@ -74,7 +75,7 @@ internal_setent (FILE **stream)
 
   if (*stream == NULL)
     {
-      *stream = fopen (DATAFILE, "rce");
+      *stream = __nss_files_fopen (DATAFILE);
 
       if (*stream == NULL)
 	status = errno == EAGAIN ? NSS_STATUS_TRYAGAIN : NSS_STATUS_UNAVAIL;

nss/nss_files/files-alias.c

@@ -29,6 +29,7 @@
 #include <kernel-features.h>
 
 #include "nsswitch.h"
+#include <nss_files.h>
 
 NSS_DECLARE_MODULE_FUNCTIONS (files)
 
@@ -49,7 +50,7 @@ internal_setent (FILE **stream)
 
   if (*stream == NULL)
     {
-      *stream = fopen ("/etc/aliases", "rce");
+      *stream = __nss_files_fopen ("/etc/aliases");
 
       if (*stream == NULL)
 	status = errno == EAGAIN ? NSS_STATUS_TRYAGAIN : NSS_STATUS_UNAVAIL;
@@ -215,7 +216,7 @@ get_next_alias (FILE *stream, const char *match, struct aliasent *result,
 
 		      first_unused = cp;
 
-		      listfile = fopen (&cp[9], "rce");
+		      listfile = __nss_files_fopen (&cp[9]);
 		      /* If the file does not exist we simply ignore
 			 the statement.  */
 		      if (listfile != NULL

nss/nss_files/files-initgroups.c

@@ -26,6 +26,7 @@
 #include <stdlib.h>
 #include <scratch_buffer.h>
 #include <nss.h>
+#include <nss_files.h>
 
 NSS_DECLARE_MODULE_FUNCTIONS (files)
 
@@ -34,16 +35,13 @@ _nss_files_initgroups_dyn (const char *user, gid_t group, long int *start,
 			   long int *size, gid_t **groupsp, long int limit,
 			   int *errnop)
 {
-  FILE *stream = fopen ("/etc/group", "rce");
+  FILE *stream = __nss_files_fopen ("/etc/group");
   if (stream == NULL)
     {
       *errnop = errno;
       return *errnop == ENOMEM ? NSS_STATUS_TRYAGAIN : NSS_STATUS_UNAVAIL;
     }
 
-  /* No other thread using this stream.  */
-  __fsetlocking (stream, FSETLOCKING_BYCALLER);
-
   char *line = NULL;
   size_t linelen = 0;
   enum nss_status status = NSS_STATUS_SUCCESS;

nss/nss_files/files-netgrp.c

@@ -26,6 +26,7 @@
 #include <string.h>
 #include "nsswitch.h"
 #include "netgroup.h"
+#include <nss_files.h>
 
 NSS_DECLARE_MODULE_FUNCTIONS (files)
 
@@ -64,7 +65,7 @@ _nss_files_setnetgrent (const char *group, struct __netgrent *result)
     return NSS_STATUS_UNAVAIL;
 
   /* Find the netgroups file and open it.  */
-  fp = fopen (DATAFILE, "rce");
+  fp = __nss_files_fopen (DATAFILE);
   if (fp == NULL)
     status = errno == EAGAIN ? NSS_STATUS_TRYAGAIN : NSS_STATUS_UNAVAIL;
   else
@@ -78,8 +79,6 @@ _nss_files_setnetgrent (const char *group, struct __netgrent *result)
       status = NSS_STATUS_NOTFOUND;
       result->cursor = result->data;
 
-      __fsetlocking (fp, FSETLOCKING_BYCALLER);
-
       while (!feof_unlocked (fp))
 	{
 	  ssize_t curlen = getline (&line, &line_len, fp);

nss/nss_files_fopen.c

@@ -0,0 +1,47 @@
+/* Open an nss_files database file.
+   Copyright (C) 2020 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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <nss_files.h>
+
+#include <errno.h>
+#include <stdio_ext.h>
+
+FILE *
+__nss_files_fopen (const char *path)
+{
+  FILE *fp = fopen (path, "rce");
+  if (fp == NULL)
+    return NULL;
+
+  /* The stream is not shared across threads.  */
+  __fsetlocking (fp, FSETLOCKING_BYCALLER);
+
+  /* This tells libio that the file is seekable, and that fp->_offset
+     is correct, ensuring that __ftello64 is efficient (bug 26257).  */
+  if (__fseeko64 (fp, 0, SEEK_SET) < 0)
+    {
+      /* nss_files requires seekable files, to deal with repeated
+         reads of the same line after reporting ERANGE.  */
+      fclose (fp);
+      __set_errno (ESPIPE);
+      return NULL;
+    }
+
+  return fp;
+}
+libc_hidden_def (__nss_files_fopen)