Re: [PATCH] ptrace: Allow other threads to access tracee

[Oleg Nesterov]

On 03/11, Jim Newsome wrote:
>
> I suppose even if the corruption of the register-values-themselves is
> acceptable, some synchronization may be needed to avoid the possibility
> of corrupting the kernel's data structures?

Yes, the kernel can crash. Just look at the comment above ptrace_freeze_traced().
The kernel assumes that the tracee is frozen, in particular it can't exit.
Say, ptrace_peek_siginfo() can crash the tracee exits and clears ->sighand,
and this can obviously happen if another thread does PTRACE_CONT + SIGKILL.

> Is it "just" a matter of adding some locking? Would a relatively coarse
> lock on the target task over the duration of the ptrace call

Yes I think needs a mutex in task_struct. But honestly I am not sure
it makes sense.... I dunno.

> (which I
> believe is always non-blocking?)

Why? It is blocking.

Oleg.