4 ms·

linux namespaces can be aggressively locked down. for example sandstorm by kenton varda has not been vulnerable to any of the recent linux kernel vulnerabilitie

linux namespaces can be aggressively locked down. for example sandstorm by kenton varda has not been vulnerable to any of the recent linux kernel vulnerabilities except for badiret and a TLB bug (https://github.com/sandstorm-io/sandstorm/blob/master/docs/using/security-non-events.md https://github.com/sandstorm-io/sandstorm/blob/master/docs/u...). it certainly wasn't vulnerable to dirty cow which is quite difficult to protect against. however, i think docker may have been vulnerable against dirty cow. [https://github.com/gebl/dirtycow-docker-vdso https://github.com/gebl/dirtycow-docker-vdso] i'm not sure if this was before or after jessie's work on securing docker. also, i don't think gvisor would have been vulnerable to dirty cow. it looks like it 'gates' all the mmap/munmap/madvise syscalls through a sentry process which does some kind of emulation of virtual memory through some magic. [https://github.com/google/gvisor/blob/797cda301677abc8523d5a2a8d731312cc43bce4/pkg/sentry/mm/README.md https://github.com/google/gvisor/blob/797cda301677abc8523d5a...]. like ultimately, i think mmap() system calls need to be executed in the monitored process but i think they are only done by the sentry using ptrace and if the sentry dies then i assume it is the root of the pid namespace so the process it is monitoring is killed as well.

amscanne 8y ago
DirtyCOW requires either ptrace or /proc/PID/mem, neither of which are accessible natively via gVisor. Even if they were, the VDSO is isolated, which was a good vector for privilege escalation. I don’t think “locked down namespaces” means anything. Sandstorm was not vulnerable because it doesn’t mount /proc and doesn’t allow ptrace.
kentonv 8y ago
It's been a while, but IIRC Docker wasn't affected by Dirty COW because they mount /proc read-only. (Sandstorm was unaffected because it doesn't mount /proc at all.) FWIW I haven't kept the security non-events up to date over the past year or two. There was at least one Linux kernel bug I can remember last year (CVE-2017-5123) that allowed a breakout from all container engines, because waitid() is too important a syscall to block. However, the vulnerability was newly-introduced and hadn't made its way into too many distros before it was fixed.

amscanne 8y ago

DirtyCOW requires either ptrace or /proc/PID/mem, neither of which are accessible natively via gVisor. Even if they were, the VDSO is isolated, which was a good vector for privilege escalation. I don’t think “locked down namespaces” means anything. Sandstorm was not vulnerable because it doesn’t mount /proc and doesn’t allow ptrace.

kentonv 8y ago

It's been a while, but IIRC Docker wasn't affected by Dirty COW because they mount /proc read-only. (Sandstorm was unaffected because it doesn't mount /proc at all.) FWIW I haven't kept the security non-events up to date over the past year or two. There was at least one Linux kernel bug I can remember last year (CVE-2017-5123) that allowed a breakout from all container engines, because waitid() is too important a syscall to block. However, the vulnerability was newly-introduced and hadn't made its way into too many distros before it was fixed.