Re: [PATCH v6 1/2] ptrace,syscall_user_dispatch: Implement Syscall User Dispatch Suspension

From: Gregory Price
Date: Wed Jan 25 2023 - 23:43:42 EST


On Thu, Jan 26, 2023 at 01:30:08AM +0100, Oleg Nesterov wrote:
> On 01/24, Gregory Price wrote:
> >
> > Adds PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH to ptrace options, and
> > modify Syscall User Dispatch to suspend interception when enabled.
> >
> > This is modeled after the SUSPEND_SECCOMP feature, which suspends
> > SECCOMP interposition. Without doing this, software like CRIU will
> > inject system calls into a process and be intercepted by Syscall
> > User Dispatch, either causing a crash (due to blocked signals) or
> > the delivery of those signals to a ptracer (not the intended behavior).
>
> Cough... Gregory, I am sorry ;)
>
> but can't we drop this patch to ?
>
> CRIU needs to do PTRACE_SET_SYSCALL_USER_DISPATCH_CONFIG and check
> config->mode anyway as we discussed.
>
> Then it can simply set *config->selector = SYSCALL_DISPATCH_FILTER_ALLOW
> with the same effect, no?
>
> Oleg.
>

After further investigation, I believe we can drop 1/2, but for a
different reason: It's actually insane behavior during the quiesce
phase. Quiesce allows the program to run until a particular state,
which means we can't turn it off lest we interfere with intended
behavior - (cough cough prior review said this cough cough i'm dumb).

I'll drop patch 1/2 and resubmit (there's an unused variable warning i
need to clean up).

Thanks again for the reviews all
~Gregory