gshadow: Matching sgetsgent, sgetsgent_r ERANGE handling (bug 30151)

Before this change, sgetsgent_r did not set errno to ERANGE, but
sgetsgent only check errno, not the return value from sgetsgent_r.
Consequently, sgetsgent did not detect any error, and reported
success to the caller, without initializing the struct sgrp object
whose address was returned.

This commit changes sgetsgent_r to set errno as well.  This avoids
similar issues in applications which only change errno.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
(cherry picked from commit 969e9733c7)

NEWS

@@ -73,6 +73,7 @@ The following bugs are resolved with this release:
   [29951] time: Set daylight to 1 for matching DST/offset change
   [29953] x86: Check minimum/maximum of non_temporal_threshold
   [30053] time: strftime %s returns -1 after 2038 on 32 bits systems
+  [30151] gshadow: Matching sgetsgent, sgetsgent_r ERANGE handling
 
 
 Version 2.35

gshadow/Makefile

@@ -26,7 +26,7 @@ headers		= gshadow.h
 routines	= getsgent getsgnam sgetsgent fgetsgent putsgent \
 		  getsgent_r getsgnam_r sgetsgent_r fgetsgent_r
 
-tests = tst-gshadow tst-putsgent tst-fgetsgent_r
+tests = tst-gshadow tst-putsgent tst-fgetsgent_r tst-sgetsgent
 
 CFLAGS-getsgent_r.c += -fexceptions
 CFLAGS-getsgent.c += -fexceptions

gshadow/sgetsgent_r.c

@@ -61,7 +61,10 @@ __sgetsgent_r (const char *string, struct sgrp *resbuf, char *buffer,
       buffer[buflen - 1] = '\0';
       sp = strncpy (buffer, string, buflen);
       if (buffer[buflen - 1] != '\0')
-	return ERANGE;
+	{
+	  __set_errno (ERANGE);
+	  return ERANGE;
+	}
     }
   else
     sp = (char *) string;

gshadow/tst-sgetsgent.c

@@ -0,0 +1,69 @@
+/* Test large input for sgetsgent (bug 30151).
+   Copyright (C) 2023 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 <gshadow.h>
+#include <stddef.h>
+#include <support/check.h>
+#include <support/support.h>
+#include <support/xmemstream.h>
+#include <stdlib.h>
+
+static int
+do_test (void)
+{
+  /* Create a shadow group with 1000 members.  */
+  struct xmemstream mem;
+  xopen_memstream (&mem);
+  const char *passwd = "k+zD0nucwfxAo3sw1NXUj6K5vt5M16+X0TVGdE1uFvq5R8V7efJ";
+  fprintf (mem.out, "group-name:%s::m0", passwd);
+  for (int i = 1; i < 1000; ++i)
+    fprintf (mem.out, ",m%d", i);
+  xfclose_memstream (&mem);
+
+  /* Call sgetsgent.  */
+  char *input = mem.buffer;
+  struct sgrp *e = sgetsgent (input);
+  TEST_VERIFY_EXIT (e != NULL);
+  TEST_COMPARE_STRING (e->sg_namp, "group-name");
+  TEST_COMPARE_STRING (e->sg_passwd, passwd);
+  /* No administrators.  */
+  TEST_COMPARE_STRING (e->sg_adm[0], NULL);
+  /* Check the members list.  */
+  for (int i = 0; i < 1000; ++i)
+    {
+      char *member = xasprintf ("m%d", i);
+      TEST_COMPARE_STRING (e->sg_mem[i], member);
+      free (member);
+    }
+  TEST_COMPARE_STRING (e->sg_mem[1000], NULL);
+
+  /* Check that putsgent brings back the input string.  */
+  xopen_memstream (&mem);
+  TEST_COMPARE (putsgent (e, mem.out), 0);
+  xfclose_memstream (&mem);
+  /* Compare without the trailing '\n' that putsgent added.  */
+  TEST_COMPARE (mem.buffer[mem.length - 1], '\n');
+  mem.buffer[mem.length - 1] = '\0';
+  TEST_COMPARE_STRING (mem.buffer, input);
+
+  free (mem.buffer);
+  free (input);
+  return 0;
+}
+
+#include <support/test-driver.c>