Re: [PATCH v8 1/2] seccomp: add a return code to trap to userspace

Oleg Nesterov
2018-11-30T10:17:56Z

On 11/29, Tycho Andersen wrote:
>
> /*
> * These should never be seen by user programs. To return one of ERESTART*
> * codes, signal_pending() MUST be set. Note that ptrace can observe these
> * at syscall exit tracing, but they will never be left for the debugged user
> * process to see.
> */
> #define ERESTARTSYS 512
>
> So basically, if you respond with -ERESTARTSYS with no signal pending, you'll
> leak it to userspace.

Yes,

> It turns out this is already possible with
> SECCOMP_RET_TRAP (and probably ptrace alone,

Yes,

> The question is: do we care?

I think we do not care, debugger can do anything with the tracee.

Oleg.