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Re: [Qemu-devel] [PATCH] Add syscalls for -runas and -chroot tothe secco
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] [PATCH] Add syscalls for -runas and -chroot tothe seccomp sandbox |
Date: |
Tue, 06 Oct 2015 07:36:02 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) |
"Namsun Ch'o" <address@hidden> writes:
>> Drawback: complexity. If we decide to limit ourselves to the original
>> threat model (rogue guest), and enter the sandbox only after setup, we
>> can keep things simpler.
>
> We could do both without much complexity. This looks simple enough to me:
>
> rc = seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(chroot), 1,
> SCMP_A0(SCMP_CMP_EQ, chroot_dir));
> if (rc < 0)
> goto seccomp_return;
>
> rc = seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(chdir), 1,
> SCMP_A0(SCMP_CMP_EQ, "/"));
> if (rc < 0)
> goto seccomp_return;
>
> The only time chroot_dir is ever used is in os-posix.c:139:
>
> if (chroot(chroot_dir) < 0) {
I'm afraid this materially weakens the sandbox. chroot_dir is writable.
We don't need to permit chroot(chroot_dir) if we enter the sandbox only
after setup.