Potential remote crashes

[Timo Sirainen]

Did a small code audit. Looks pretty good in general, but found a few
things:

static int yy_use_redo_text(buff_t *buff)
{
    size_t used  = buff->t.leng;
    size_t size  = buff->size;
    size_t avail = size - used;
    byte  *buf = buff->t.text+used;
    size_t count = min(yysave->size, avail-2);

    memcpy(buf, yysave->t.text, count );

If avail is 0 or 1, count is set to (size_t)-1 or -2 and memcpy()
crashes. I'm not sure if that can happen though, it's not so obvious
when and how this function gets called..

size_t qp_decode(word_t *word)
..
    while (s < e)
    {
	byte ch = *s++;
	if (ch == '=') {
	    ch = *s++;
	    if (ch != '\n') {
		byte cx = *s++;
..
		    *d++ = '=';
		    *d++ = ch;
		    *d++ = cx;
		    continue;
..
    *d = '\0';

If ch == '=' is missing checks if s still is less than e, but it still
updates d. Looks like that would allow writing \0 to 1 or 2 bytes after
malloc()ed data.