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SubjectRe: [PULL] seccomp update (next)
On Fri, Jun 17, 2016 at 12:15 AM, James Morris <jmorris@namei.org> wrote:
> On Tue, 14 Jun 2016, Kees Cook wrote:
>
>> Hi,
>>
>> Please pull these seccomp changes for next. These have been tested by
>> myself and Andy, and close a long-standing issue with seccomp where tracers
>> could change the syscall out from under seccomp.
>
> Pulled to security -next.

As a heads up: I think this doesn't quite close the hole on x86. Consider:

64-bit task arranges to be traced by a 32-bit task (or presumably a
64-bit task that calls ptrace via int80).

Tracer does PTRACE_SYSCALL.

Tracee does a normal syscall.

Tracer writes tracee's orig_ax, thus invoking this thing in
arch/x86/kernel/ptrace.c:

if (syscall_get_nr(child, regs) >= 0)
child->thread.status |= TS_COMPAT;

Tracer resumes and gets confused.

I think the right fix is to just delete:

if (syscall_get_nr(child, regs) >= 0)
child->thread.status |= TS_COMPAT;

from ptrace.c. The comment above it is garbage, too.

--Andy

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