wcsstr: Ensure worst-case linear execution time.

* lib/wchar.in.h (wcsstr): Consider REPLACE_WCSSTR.
* lib/wcs-two-way.h: New file, based on lib/str-two-way.h.
* lib/wcsstr-impl.h: If requested, use the two-way algorithm. New code
based on lib/strstr.c.
* m4/wcsstr.m4 (gl_FUNC_WCSSTR_SIMPLE): Renamed from gl_FUNC_WCSSTR.
(gl_FUNC_WCSSTR): New macro, based on gl_FUNC_STRSTR in m4/strstr.m4.
* m4/wchar_h.m4 (gl_WCHAR_H_DEFAULTS): Initialize REPLACE_WCSSTR.
* modules/wchar (Makefile.am): Substitute REPLACE_WCSSTR.
* modules/wcsstr-simple: New file, based on modules/wcsstr.
* modules/wcsstr (Description): Document that this module now provides
an efficient implementation.
(Files): Add lib/wcs-two-way.h.
(Depends-on): Depend on wcsstr-simple and the dependencies of the
two-way implementation.
(configure.ac): Use AC_LIBOBJ instead of a conditional. Don't invoke
gl_WCHAR_MODULE_INDICATOR.
(Makefile.am): Don't augment lib_SOURCES.
* tests/test-wcsstr.c: New file, based on tests/test-strstr.c.
* modules/wcsstr-tests: New file, based on modules/strstr-tests.
* doc/posix-functions/wcsstr.texi: Mention the worst-case complexity.
Mention the new 'wcsstr-simple' module.
* doc/posix-functions/strstr.texi: Fix typo.

1 files changed, 274 insertions, 0 deletions

diff --git a/tests/test-wcsstr.c b/tests/test-wcsstr.c
new file mode 100644
index 0000000000..5bc671124a
--- /dev/null
+++ b/tests/test-wcsstr.c
@@ -0,0 +1,274 @@
+/*
+ * Copyright (C) 2004, 2007-2023 Free Software Foundation, Inc.
+ * Written by Bruno Haible and Eric Blake
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+#include <wchar.h>
+
+#include "signature.h"
+SIGNATURE_CHECK (wcsstr, wchar_t *, (wchar_t const *, wchar_t const *));
+
+#include <signal.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "zerosize-ptr.h"
+#include "macros.h"
+
+int
+main (int argc, char *argv[])
+{
+#if HAVE_DECL_ALARM
+  /* Declare failure if test takes too long, by using default abort
+     caused by SIGALRM.  All known platforms that lack alarm also have
+     a quadratic wcsstr, and the replacement wcsstr is known to not
+     take too long.  */
+  int alarm_value = 50;
+  signal (SIGALRM, SIG_DFL);
+  alarm (alarm_value);
+#endif
+
+  {
+    const wchar_t input[] = L"foo";
+    const wchar_t *result = wcsstr (input, L"");
+    ASSERT (result == input);
+  }
+
+  {
+    const wchar_t input[] = L"foo";
+    const wchar_t *result = wcsstr (input, L"o");
+    ASSERT (result == input + 1);
+  }
+
+  {
+    /* On some platforms, the memchr() functions reads past the first
+       occurrence of the byte to be searched, leading to an out-of-bounds
+       read access for wcsstr().
+       See <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737>.
+       This is a bug in memchr(), see the Austin Group's clarification
+       <https://www.opengroup.org/austin/docs/austin_454.txt>.  */
+    const wchar_t *fix = L"aBaaaaaaaaaaax";
+    wchar_t *page_boundary = (wchar_t *) zerosize_ptr ();
+    size_t len = wcslen (fix) + 1;
+    wchar_t *input =
+      page_boundary ? page_boundary - len : malloc (len * sizeof (wchar_t));
+    const wchar_t *result;
+
+    wcscpy (input, fix);
+    result = wcsstr (input, L"B1x");
+    ASSERT (result == NULL);
+    if (!page_boundary)
+      free (input);
+  }
+
+  {
+    const wchar_t input[] = L"ABC ABCDAB ABCDABCDABDE";
+    const wchar_t *result = wcsstr (input, L"ABCDABD");
+    ASSERT (result == input + 15);
+  }
+
+  {
+    const wchar_t input[] = L"ABC ABCDAB ABCDABCDABDE";
+    const wchar_t *result = wcsstr (input, L"ABCDABE");
+    ASSERT (result == NULL);
+  }
+
+  {
+    const wchar_t input[] = L"ABC ABCDAB ABCDABCDABDE";
+    const wchar_t *result = wcsstr (input, L"ABCDABCD");
+    ASSERT (result == input + 11);
+  }
+
+  /* Check that a long periodic needle does not cause false positives.  */
+  {
+    const wchar_t input[] = L"F_BD_CE_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD"
+                             "_C3_88_20_EF_BF_BD_EF_BF_BD_EF_BF_BD"
+                             "_C3_A7_20_EF_BF_BD";
+    const wchar_t need[] = L"_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD";
+    const wchar_t *result = wcsstr (input, need);
+    ASSERT (result == NULL);
+  }
+  {
+    const wchar_t input[] = L"F_BD_CE_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD"
+                             "_C3_88_20_EF_BF_BD_EF_BF_BD_EF_BF_BD"
+                             "_C3_A7_20_EF_BF_BD_DA_B5_C2_A6_20"
+                             "_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD";
+    const wchar_t need[] = L"_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD_EF_BF_BD";
+    const wchar_t *result = wcsstr (input, need);
+    ASSERT (result == input + 115);
+  }
+
+  /* Check that a very long haystack is handled quickly if the needle is
+     short and occurs near the beginning.  */
+  {
+    size_t repeat = 10000;
+    size_t m = 1000000;
+    const wchar_t *needle =
+      L"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
+       "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
+    wchar_t *haystack = (wchar_t *) malloc ((m + 1) * sizeof (wchar_t));
+    if (haystack != NULL)
+      {
+        wmemset (haystack, L'A', m);
+        haystack[0] = L'B';
+        haystack[m] = L'\0';
+
+        for (; repeat > 0; repeat--)
+          {
+            ASSERT (wcsstr (haystack, needle) == haystack + 1);
+          }
+
+        free (haystack);
+      }
+  }
+
+  /* Check that a very long needle is discarded quickly if the haystack is
+     short.  */
+  {
+    size_t repeat = 10000;
+    size_t m = 1000000;
+    const wchar_t *haystack =
+      L"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
+       "ABABABABABABABABABABABABABABABABABABABABABABABABABABABABABABABABABAB";
+    wchar_t *needle = (wchar_t *) malloc ((m + 1) * sizeof (wchar_t));
+    if (needle != NULL)
+      {
+        wmemset (needle, L'A', m);
+        needle[m] = L'\0';
+
+        for (; repeat > 0; repeat--)
+          {
+            ASSERT (wcsstr (haystack, needle) == NULL);
+          }
+
+        free (needle);
+      }
+  }
+
+  /* Check that the asymptotic worst-case complexity is not quadratic.  */
+  {
+    size_t m = 1000000;
+    wchar_t *haystack = (wchar_t *) malloc ((2 * m + 2) * sizeof (wchar_t));
+    wchar_t *needle = (wchar_t *) malloc ((m + 2) * sizeof (wchar_t));
+    if (haystack != NULL && needle != NULL)
+      {
+        const wchar_t *result;
+
+        wmemset (haystack, L'A', 2 * m);
+        haystack[2 * m] = L'B';
+        haystack[2 * m + 1] = L'\0';
+
+        wmemset (needle, L'A', m);
+        needle[m] = L'B';
+        needle[m + 1] = L'\0';
+
+        result = wcsstr (haystack, needle);
+        ASSERT (result == haystack + m);
+      }
+    free (needle);
+    free (haystack);
+  }
+
+  /* Sublinear speed is only possible in memmem; wcsstr must examine
+     every character of haystack to find its length.  */
+
+
+  {
+    /* Ensure that with a barely periodic "short" needle, wcsstr's
+       search does not mistakenly skip just past the match point.  */
+    const wchar_t *haystack =
+      L"\n"
+       "with_build_libsubdir\n"
+       "with_local_prefix\n"
+       "with_gxx_include_dir\n"
+       "with_cpp_install_dir\n"
+       "enable_generated_files_in_srcdir\n"
+       "with_gnu_ld\n"
+       "with_ld\n"
+       "with_demangler_in_ld\n"
+       "with_gnu_as\n"
+       "with_as\n"
+       "enable_largefile\n"
+       "enable_werror_always\n"
+       "enable_checking\n"
+       "enable_coverage\n"
+       "enable_gather_detailed_mem_stats\n"
+       "enable_build_with_cxx\n"
+       "with_stabs\n"
+       "enable_multilib\n"
+       "enable___cxa_atexit\n"
+       "enable_decimal_float\n"
+       "enable_fixed_point\n"
+       "enable_threads\n"
+       "enable_tls\n"
+       "enable_objc_gc\n"
+       "with_dwarf2\n"
+       "enable_shared\n"
+       "with_build_sysroot\n"
+       "with_sysroot\n"
+       "with_specs\n"
+       "with_pkgversion\n"
+       "with_bugurl\n"
+       "enable_languages\n"
+       "with_multilib_list\n";
+    const wchar_t *needle =
+      L"\n"
+       "with_gnu_ld\n";
+    const wchar_t* p = wcsstr (haystack, needle);
+    ASSERT (p - haystack == 114);
+  }
+
+  {
+    /* Same bug, shorter trigger.  */
+    const wchar_t *haystack = L"..wi.d.";
+    const wchar_t *needle = L".d.";
+    const wchar_t* p = wcsstr (haystack, needle);
+    ASSERT (p - haystack == 4);
+  }
+
+  /* Test case from Yves Bastide.
+     <https://www.openwall.com/lists/musl/2014/04/18/2>  */
+  {
+    const wchar_t input[] = L"playing play play play always";
+    const wchar_t *result = wcsstr (input, L"play play play");
+    ASSERT (result == input + 8);
+  }
+
+  /* Test long needles.  */
+  {
+    size_t m = 1024;
+    wchar_t *haystack = (wchar_t *) malloc ((2 * m + 1) * sizeof (wchar_t));
+    wchar_t *needle = (wchar_t *) malloc ((m + 1) * sizeof (wchar_t));
+    if (haystack != NULL && needle != NULL)
+      {
+        const wchar_t *p;
+        haystack[0] = L'x';
+        wmemset (haystack + 1, L' ', m - 1);
+        wmemset (haystack + m, L'x', m);
+        haystack[2 * m] = L'\0';
+        wmemset (needle, L'x', m);
+        needle[m] = L'\0';
+        p = wcsstr (haystack, needle);
+        ASSERT (p);
+        ASSERT (p - haystack == m);
+      }
+    free (needle);
+    free (haystack);
+  }
+
+  return 0;
+}