[krbdev.mit.edu #6959] cms_signeddata_verify has unsafe error handling

[Sam Hartman via RT]

I felt the need to add the following comment to cms_signeddata_verify

    /*                                                                          
     * Warning: Since most openssl functions do not set retval, large chunks of
     * this function assume that retval is always a failure and may go to       
     * cleanup without setting retval explicitly. Make sure retval is not set   
     * to 0 or errors such as signature verification failure may be converted   
     * to success with significant security consequences.                       

If anyone accidentally inserted a k5alloc or anything else that set retval, it would be really bad.
I'd recommend refactoring that function.
Since I'm not doing that now I'm opening a bug to track.