Re: [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex

Bernd Edlinger
2020-03-09T13:45:57Z

On 3/8/20 10:38 PM, Eric W. Biederman wrote:
>
> The cred_guard_mutex is problematic. The cred_guard_mutex is held
> over the userspace accesses as the arguments from userspace are read.
> The cred_guard_mutex is held of PTRACE_EVENT_EXIT as the the other

... is held while waiting for the trace parent to handle PTRACE_EVENT_EXIT
or something?

I wonder if we also should mention that
it is held while waiting for the trace parent to
receive the exit code with "wait"?

> threads are killed. The cred_guard_mutex is held over
> "put_user(0, tsk->clear_child_tid)" in exit_mm().
>
> Any of those can result in deadlock, as the cred_guard_mutex is held
> over a possible indefinite userspace waits for userspace.
>
> Add exec_update_mutex that is only held over exec updating process

Add ?

> with the new contents of exec, so that code that needs not to be
> confused by exec changing the mm and the cred in ways that can not
> happen during ordinary execution of a process.
>
> The plan is to switch the users of cred_guard_mutex to
> exec_udpate_mutex one by one. This lets us move forward while still

s/udpate/update/

Bernd.