On Wed, Feb 12, 2014 at 01:50:35PM -0800, Kees Cook wrote: > On Wed, Feb 12, 2014 at 1:32 PM, Andrew Morton > <a...@linux-foundation.org> wrote: > > On Wed, 12 Feb 2014 19:40:11 +0400 Andrey Vagin <ava...@openvz.org> wrote: > > > >> Currently prctl_set_mm requires the global CAP_SYS_RESOURCE, > >> this patch reduce requiremence to CAP_SYS_RESOURCE in the current > >> namespace. > >> > >> When we restore a task we need to set up text, data and data heap sizes > >> from userspace to the values a task had at checkpoint time. > >> > >> Currently we can not restore these parameters, if a task lives in > >> a non-root user name space, because it has no capabilities in the > >> parent namespace. > >> > >> prctl_set_mm() changes parameters of the current task and doesn't affect > >> other tasks. > >> > >> This patch affects the RLIMIT_DATA limit, because a consumtiuon is > >> calculated relatively to mm->end_data, mm->start_data, mm->start_brk. > > > > I can't for the life of me work out what you were trying to say here. > > Please fix and resend this paragraph? > > > >> rlim = rlimit(RLIMIT_DATA); > >> if (rlim < RLIM_INFINITY && (brk - mm->start_brk) + > >> (mm->end_data - mm->start_data) > rlim) > >> goto out; > >> > >> This limit affects calls to brk() and sbrk(), but it doesn't affect > >> mmap. So I think requirement of CAP_SYS_RESOURCE in the current > >> namespace is enough for this limit. > >> > >> ... > >> > >> Cc: secur...@kernel.org > > > > That list is for reporting kernel security bugs. > > > >> > >> --- a/kernel/sys.c > >> +++ b/kernel/sys.c > >> @@ -1701,7 +1701,7 @@ static int prctl_set_mm(int opt, unsigned long addr, > >> if (arg5 || (arg4 && opt != PR_SET_MM_AUXV)) > >> return -EINVAL; > >> > >> - if (!capable(CAP_SYS_RESOURCE)) > >> + if (!ns_capable(current_user_ns(), CAP_SYS_RESOURCE)) > >> return -EPERM; > >> > >> if (opt == PR_SET_MM_EXE_FILE) > > > > This looks harmless. > > I want to be convinced of this, but weakening this cap check seems > like an easy way for a process to hide itself trivially from the real > root user. It can change it's exe file link, and dodge RLIMIT_DATA by > changing the brk addresses. The whole reason this cap check was there > was to stop that kind of thing. Limiting it to a namespace isn't great > since USER_NS means unprivileged processes can enter a new NS as the > NS root user.
All what you are describing here we are doing on restoring tasks. We need a way how to restore these parameters. One of our targets is to be able to dump and restore Linux Containers. All processes of a container live in a separate set of namespaces. I was thinking to restore these parameters before entering into userns, but this idea failed, because a process can't enter in pidns, but pidns must be created in userns... >> It can change it's exe file link We can change memory content with help of ptrace. So if we want to hide a process, we can execute another process and inject our code into it. It can be equivalent to changing exe file link. Yes, it's a bit harder, but we can do that even without this patch. >> dodge RLIMIT_DATA This limit affects calls to brk(2) and sbrk(2). But a task can use mmap() to allocate memory. How is this limit used? Sorry if I miss something. > > -Kees > > -- > Kees Cook > Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
