Harden File Read From Symbolic Links

[zakuArbor]

Purpose

• previous change [Security] Link File Attack #47 tried to address preventing symbolic link attacks but it is still vulnerable to TOCTOU and I assume hardlinks as well
• inspiration: https://lwn.net/Articles/939217/
  • That open() call also uses the O_NOFOLLOW flag
  • however, could open the door to a time-of-check-to-time-of-use vulnerability
• source: https://wiki.sei.cmu.edu/confluence/display/c/POS01-C.+Check+for+the+existence+of+links+when+dealing+with+files

Tasks/Goals

• Open file with nofollow flag
• Check if file has been tampered
• Prevent hard links

Summary

To fill out once the issue is to be closed. Give a short summary of the changes you made to implement or fix an issue

[zakuArbor]

Checkout https://wiki.sei.cmu.edu/confluence/display/c/POS35-C.+Avoid+race+conditions+while+checking+for+the+existence+of+a+symbolic+link

Existing method is insufficient. Think about using open instead of fopen