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. -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/
