cups-filters 2.0rc2

Security vulnerability fix and general security and code clean-up of the beh (Backend Error Handler) backend:

• beh backend: Use execv() instead of system() - CVE-2023-24805
  With execv() command line arguments are passed as separate strings and not the full command line in a single string. This prevents arbitrary command execution by escaping the quoting of the arguments in a job with forged job title.
• beh backend: Extra checks against odd/forged input - CVE-2023-24805
  • Do not allow / in the scheme of the URI (= backend executable name), to assure that only backends inside /usr/lib/cups/backend/ are used.
  • Pre-define scheme buffer to empty string, to be defined for case of URI being NULL.
  • URI must have :, to split off scheme, otherwise error.
  • Check return value of snprintf() to create call path for the backend, to error out on truncation of a too long scheme or on complete failure due to a completely odd scheme.
• beh backend: Further improvements - CVE-2023-24805
  • Use strncat() instead of strncpy() for getting scheme from URI, the latter does not require setting terminating zero byte in case of truncation.
  • Also exclude . or .. as scheme, as directories are not valid CUPS backends.
  • Do not use fprintf() in sigterm_handler(), to not interfere with a fprintf() which could be running in the main process when sigterm_handler() is triggered.
  • Use static volatile int for global variable job_canceled.
• parallel backend: Added missing #include lines