Re: [Qemu-devel] [PULL 1/2] seccomp: don't kill process for resource control syscalls

[Daniel P . Berrangé]

On Wed, Mar 27, 2019 at 10:59:03AM +0100, Eduardo Otubo wrote:
> From: Daniel P. Berrangé <address@hidden>
> 
> The Mesa library tries to set process affinity on some of its threads in
> order to optimize its performance. Currently this results in QEMU being
> immediately terminated when seccomp is enabled.
> 
> Mesa doesn't consider failure of the process affinity settings to be
> fatal to its operation, but our seccomp policy gives it no choice in
> gracefully handling this denial.
> 
> It is reasonable to consider that malicious code using the resource
> control syscalls to be a less serious attack than if they were trying
> to spawn processes or change UIDs and other such things. Generally
> speaking changing the resource control setting will "merely" affect
> quality of service of processes on the host. With this in mind, rather
> than kill the process, we can relax the policy for these syscalls to
> return the EPERM errno value. This allows callers to detect that QEMU
> does not want them to change resource allocations, and apply some
> reasonable fallback logic.
> 
> The main downside to this is for code which uses these syscalls but does
> not check the return value, blindly assuming they will always
> succeeed. Returning an errno could result in sub-optimal behaviour.
> Arguably though such code is already broken & needs fixing regardless.
> 
> Signed-off-by: Daniel P. Berrangé <address@hidden>
> Reviewed-by: Marc-André Lureau <address@hidden>
> Acked-by: Eduardo Otubo <address@hidden>

Normally the person sending the pull request should be adding a
Signed-off-by line, not an Acked-by line, as Acked-by doesn't
have any meaning wrt to the DCO.

IIUC, we don't really use Acked-by in QEMU. Only case I think
it would be used is where a maintainer is giving their approval
for a patch to be sent someone else's tree. eg if a seccomp patch
had to merge via a block maintainer tree for some reason, then
you could give an Acked-by to indicate you are ok with that going
via the different tree.

Regards,
Daniel
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