[BUG] afs_deliver_to_call -- ASSERTCMP when a server returns zero capabilities

[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/131-afs-assertcmp-zero-capabilities/

  AFS: Assertion failed
  1 > 2 is false
  0x1 > 0x2 is false
  kernel BUG at fs/afs/rxrpc.c:572!
  Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
  Workqueue: kafsd afs_process_async_call
  Call Trace:
   afs_process_async_call+0x82/0xe0
   process_scheduled_works+0xc99/0x1900
   worker_thread+0xa53/0xfc0
   kthread+0x38b/0x480
   ret_from_fork+0x514/0xb70
  Kernel panic - not syncing: Fatal exception

Our reproducer.c is available upon request.

Happy to test a patch if that would help.

Regards,