On 3/8/20 10:34 PM, Eric W. Biederman wrote:

Bernd, everyone

This is how I think the infrastructure change should look that makes way
for fixing this issue.

- Cleanup and reorder the code so code that can potentially wait
  indefinitely for userspace comes at the beginning for flush_old_exec.
- Add a new mutex and take it after we have passed any potential
  indefinite waits for userspace.

Then I think it is just going through the existing users of
cred_guard_mutex and fixing them to use the new one.

There really aren't that many users of cred_guard_mutex so we should be
able to get through the easy ones fairly quickly.  And anything that
isn't easy we can wait until we have a good fix.

The users of cred_guard_mutex that I saw were:
    fs/proc/base.c:
       proc_pid_attr_write
       do_io_accounting
       proc_pid_stack
       proc_pid_syscall
       proc_pid_personality
    
    perf_event_open
    mm_access
    kcmp
    pidfd_fget
    seccomp_set_mode_filter

Bernd I think I have addressed the issues you pointed out in v1.
Please let me know if you see anything else.

Yes, looks good, except some nits.


Thanks
Bernd.