binfmt_misc: fix false -ENOEXEC when coupled with other binary handlers

In case the binfmt_misc binary handler is registered *before* the e.g.
script one (when for example being compiled as a module) the following
situation may occur:

1. user launches a script, whose interpreter is a misc binary;
2. the load_misc_binary sets the misc_bang and returns -ENOEVEC,
since the binary is a script;
3. the load_script_binary loads one and calls for search_binary_hander
to run the interpreter;
4. the load_misc_binary is called again, but refuses to load the
binary due to misc_bang bit set.

The fix is to move the misc_bang setting lower - prior to the actual
call to the search_binary_handler.

Caused by the commit 3a2e7f47 (binfmt_misc.c: avoid potential kernel
stack overflow)

Signed-off-by: Pavel Emelyanov <[e-mail]>
Reported-by: Kirill A. Shutemov <[e-mail]>
Tested-by: Kirill A. Shutemov <[e-mail]>
Cc: <[e-mail]> [2.6.26.x]
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/binfmt_misc.c

···
 	if (bprm->misc_bang)
 		goto _ret;
 
-	bprm->misc_bang = 1;
-
 	/* to keep locking time low, we copy the interpreter string */
 	read_lock(&entries_lock);
 	fmt = check_file(bprm);
···
 
 	if (retval < 0)
 		goto _error;
+
+	bprm->misc_bang = 1;
 
 	retval = search_binary_handler (bprm, regs);
 	if (retval < 0)