getopt: fix fencepost error in ambiguous-W-option handling

getopt_long contains an undocumented (AFAICT) feature in which, if you
put "W;" in the short-options list, then '-W foo' and '-Wfoo' are
treated as equivalent to '--foo'.  This is implemented with a partial
second copy of the code for handling long options, and that code
increments optind one too many times when recovering from an ambiguous
abbreviated option, which can cause the main loop to walk past the end
of argv and crash.

I discovered this while writing a test case that tries to exercise all
of getopt's error reporting paths; I wouldn't be surprised to learn
that this feature is never used by real applications.

	* posix/getopt.c (_getopt_internal_r): Don't increment
	d->optind a second time when reporting ambiguous -W options.

2 files changed, 3 insertions, 1 deletions

diff --git a/ChangeLog b/ChangeLog
index ba702c0efd..48e5b036d9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2017-04-07  Zack Weinberg  <zackw@panix.com>
 
+	* posix/getopt.c (_getopt_internal_r): Don't increment
+	d->optind a second time when reporting ambiguous -W options.
+
 	* posix/getopt_int.h: Include getopt.h.
 	Use impl-namespace names for all arguments to _getopt_internal and
 	_getopt_internal_r.
diff --git a/posix/getopt.c b/posix/getopt.c
index f1fa0166d8..e616aa6e4d 100644
--- a/posix/getopt.c
+++ b/posix/getopt.c
@@ -850,7 +850,6 @@ _getopt_internal_r (int argc, char *const *argv, const char *optstring,
 #endif
 	      }
 	    d->__nextchar += strlen (d->__nextchar);
-	    d->optind++;
 	    return '?';
 	  }
 	if (pfound != NULL)