On 15 Feb 2016 17:50, Dmitry V. Levin wrote: > On Mon, Feb 15, 2016 at 09:30:18AM -0500, Mike Frysinger wrote: > > On 15 Feb 2016 15:21, Dmitry V. Levin wrote: > > > On Mon, Feb 15, 2016 at 12:12:09PM +0100, Pas wrote: > > > > 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 strace sees -1 in its place. > > > > > > You can play with strace/tests/seccomp.c and see it yourself. > > > > would PTRACE_O_TRACESECCOMP help here ? > > Only for SECCOMP_RET_TRACE actions.
oh i misread ... i was thinking it was for all ret operations. can we get the seccomp core to save its original state in a way we can get at later, perhaps via a new PTRACE_GETSECCOMPDATA ? that'd tell us which SECCOMP_RET_xxx was used and the value that was in there before. we would need a new PTRACE_EVENT_xxx so we don't have to run it all the time. -mike
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