Date: Thu, 3 Nov 2016 14:34:16 -0600 From: Kees Cook <keescook@...omium.org> To: Jann Horn <jann@...jh.net> Cc: Lafcadio Wluiki <wluikil@...il.com>, LKML <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com> Subject: Re: [2/2] procfs/tasks: add a simple per-task procfs hidepid= field On Thu, Nov 3, 2016 at 12:24 PM, Jann Horn <jann@...jh.net> wrote: > On Thu, Nov 03, 2016 at 09:30:38AM -0600, Lafcadio Wluiki wrote: >> This adds a new per-task hidepid= flag that is honored by procfs when >> presenting /proc to the user, in addition to the existing hidepid= mount >> option. So far, hidepid= was exclusively a per-pidns setting. Locking >> down a set of processes so that they cannot see other user's processes >> without affecting the rest of the system thus currently requires >> creation of a private PID namespace, with all the complexity it brings, >> including maintaining a stub init process as PID 1 and losing the >> ability to see processes of the same user on the rest of the system. > [...] >> diff --git a/kernel/sys.c b/kernel/sys.c >> index 89d5be4..c0a1d3e 100644 >> --- a/kernel/sys.c >> +++ b/kernel/sys.c >> @@ -2270,6 +2270,16 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, >> case PR_GET_FP_MODE: >> error = GET_FP_MODE(me); >> break; >> + case PR_SET_HIDEPID: >> + if (arg2 < HIDEPID_OFF || arg2 > HIDEPID_INVISIBLE) >> + return -EINVAL; >> + if (arg2 < me->hide_pid) >> + return -EPERM; >> + me->hide_pid = arg2; >> + break; > > Should we test for ns_capable(CAP_SYS_ADMIN)||no_new_privs here? > I think it wouldn't hurt, and I'd like to avoid adding new ways in which > the execution of setuid programs can be influenced. OTOH, people already > use hidepid now, and it's not an issue... I'm not sure. Opinions? Hrrm, I'm really on the fence. I don't feel like having things in /proc go invisible for a setuid would be bad, but I wouldn't be surprised to eat my words. :) On the other hand, I can't think of a place where this requirement would create a problem. e.g. init launching a web server as root could set nnp and this, and it would still be able to switch down to www-data, etc. If someone has www-data in their /etc/sudoers file, I already fear for their sanity. ;) -Kees -- Kees Cook Nexus Security
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