[BUG] general protection fault in security_path_post_mknod

[Farhad Alemi]

Hello,

As part of the kernel research at ASU's SEFCOM
lab, we hit the crash below. Crash reports can be found here:

  https://github.com/farhad-alemi/public_bug_reports/tree/main/178-general-protection-fault-in-security-path-post-mknod/

  Oops: general protection fault, probably for non-canonical address
0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI
  KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
  RIP: 0010:security_path_post_mknod+0x49/0x1e0 security/security.c:1430
  Call Trace:
   security_path_post_mknod+0x49/0x1e0 security/security.c:1430
   filename_mknodat+0x40e/0x660 fs/namei.c:5172
   __do_sys_mknod fs/namei.c:5207 [inline]
   __se_sys_mknod+0x3a/0x150 fs/namei.c:5204
   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
   do_syscall_64+0x146/0x480 arch/x86/entry/syscall_64.c:94
   entry_SYSCALL_64_after_hwframe+0x77/0x7f

Our reproducer.c is available upon request.

Happy to test a patch if that would help.

Regards,