fix bug with "seq -f %10 1"

[Paul Eggert]

I found this bug when I was just fooling around:

$ seq -f %10 1
seq: memory exhausted

The problem is that strchr(string, '\0') always succeeds, by
definition.  Here's a patch:

Fix bug with "seq -f %10", which is an invalid format.
* src/seq.c (long_double_format): Fix bug that mishandled this case.
* tests/misc/seq (fmt-d): New test, for this case.
diff --git a/src/seq.c b/src/seq.c
index 261a44b..b3d1e46 100644
--- a/src/seq.c
+++ b/src/seq.c
@@ -190,6 +190,7 @@ long_double_format (char const *fmt, struct layout *layout)
   size_t suffix_len = 0;
   size_t length_modifier_offset;
   bool has_L;
+  static char const allowed_specifiers[8] = "efgaEFGA";

   for (i = 0; ! (fmt[i] == '%' && fmt[i + 1] != '%'); i += (fmt[i] == '%') + 1)
     if (fmt[i])
@@ -209,7 +210,7 @@ long_double_format (char const *fmt, struct layout *layout)
   length_modifier_offset = i;
   has_L = (fmt[i] == 'L');
   i += has_L;
-  if (! strchr ("efgaEFGA", fmt[i]))
+  if (! memchr (allowed_specifiers, fmt[i], sizeof allowed_specifiers))
     return NULL;

   for (i++; ! (fmt[i] == '%' && fmt[i + 1] != '%'); i += (fmt[i] == '%') + 1)
diff --git a/tests/misc/seq b/tests/misc/seq
index 3365d95..a85da75 100755
--- a/tests/misc/seq
+++ b/tests/misc/seq
@@ -89,6 +89,11 @@ my @Tests =
     {ERR => "seq: invalid format string: `%%g'\n"
      . "Try `seq --help' for more information.\n"},
 ],
+
+   # In coreutils-6.10, this would mistakenly exhaust memory.
+   ['fmt-d',   qw(-f %%10 1), {EXIT => 1},
+    {ERR => "seq: invalid format string: `%%10'\n"
+     . "Try `seq --help' for more information.\n"}],
   );

 # Append a newline to each entry in the OUT array.