syscall_4294967295

[Dmitry V. Levin]

Hi,

On Mon, Feb 15, 2016 at 12:12:09PM +0100, Pas wrote:
> Hello!
> 
> Thanks for the quick response and for the hint! After testing with
> -fveseccomp,prctl
> it turns out that:
> 
> docker-engine 1.10.1-0~wily uses seccomp (prctl PR_SET_SECCOMP,
> SECCOMP_MODE_FILTER and PR_CAPBSET_DROP ...), whereas 1.10.1-0~jessie
> doesn't. Though eventually by default Docker will filter out (almost all?)
> syscalls:
> https://docs.docker.com/engine/reference/run/#runtime-privilege-and-linux-capabilities

On entering syscall, seccomp kernel hooks are executed before ptrace
kernel hooks.  As result, when some syscall is blocked by seccomp filter
using SECCOMP_RET_ERRNO statement, on many architectures including x86 and
x86_64 the syscall number is clobbered and straces sees -1 in its place.

You can play with strace/tests/seccomp.c and see it yourself.


-- 
ldv
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