nstrftime: suggest to glibc how to avoid alloca

* lib/nstrftime.c (widen) [COMPILE_WIDE]: Remove.
(__strftime_internal) [COMPILE_WIDE): Instead of converting the
multibyte time zone abbreviation into a potentially unbounded
alloca buffer, convert it directly into the output buffer.
Although this code is not used in Gnulib, this can help the glibc
developers avoid the problem on the glibc side.

2 files changed, 35 insertions, 14 deletions

diff --git a/ChangeLog b/ChangeLog
index ecbc25ef06..36b3c65b81 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2023-05-17  Paul Eggert  <eggert@cs.ucla.edu>
+
+	nstrftime: suggest to glibc how to avoid alloca
+	* lib/nstrftime.c (widen) [COMPILE_WIDE]: Remove.
+	(__strftime_internal) [COMPILE_WIDE): Instead of converting the
+	multibyte time zone abbreviation into a potentially unbounded
+	alloca buffer, convert it directly into the output buffer.
+	Although this code is not used in Gnulib, this can help the glibc
+	developers avoid the problem on the glibc side.
+
 2023-05-15  Bruno Haible  <bruno@clisp.org>
 
 	doc: New chapter "Strings and Characters".
diff --git a/lib/nstrftime.c b/lib/nstrftime.c
index 68bb560910..35a9307e1a 100644
--- a/lib/nstrftime.c
+++ b/lib/nstrftime.c
@@ -226,15 +226,6 @@ extern char *tzname[];
 #  undef __mbsrtowcs_l
 #  define __mbsrtowcs_l(d, s, l, st, loc) __mbsrtowcs (d, s, l, st)
 # endif
-# define widen(os, ws, l) \
-  {                                                                           \
-    mbstate_t __st;                                                           \
-    const char *__s = os;                                                     \
-    memset (&__st, '\0', sizeof (__st));                                      \
-    l = __mbsrtowcs_l (NULL, &__s, 0, &__st, loc);                            \
-    ws = (wchar_t *) alloca ((l + 1) * sizeof (wchar_t));                     \
-    (void) __mbsrtowcs_l (ws, &__s, l, &__st, loc);                           \
-  }
 #endif
 
 
@@ -1374,11 +1365,31 @@ __strftime_internal (STREAM_OR_CHAR_T *s, STRFTIME_ARG (size_t maxsize)
 #ifdef COMPILE_WIDE
           {
             /* The zone string is always given in multibyte form.  We have
-               to transform it first.  */
-            wchar_t *wczone;
-            size_t len;
-            widen (zone, wczone, len);
-            cpy (len, wczone);
+               to convert it to wide character.  */
+            size_t w = pad == L_('-') || width < 0 ? 0 : width;
+            char const *z = zone;
+            mbstate_t st = {0};
+            size_t len = __mbsrtowcs_l (p, &z, maxsize - i, &st, loc);
+            if (len == (size_t) -1)
+              return 0;
+            size_t incr = len < w ? w : len;
+            if (incr >= maxsize - i)
+              {
+                errno = ERANGE;
+                return 0;
+              }
+            if (p)
+              {
+                if (len < w)
+                  {
+                    size_t delta = w - len;
+                    wmemmove (p + delta, p, len);
+                    wchar_t wc = pad == L_('0') || pad == L_('+') ? L'0' : L' ';
+                    wmemset (p, wc, delta);
+                  }
+                p += incr;
+              }
+            i += incr;
           }
 #else
           cpy (strlen (zone), zone);